At Home in Texas

Is Excessive Back Pressure an issue with your Heating and Cooling System?

Is your heating and cooling system operating under too much internal static pressure? IS there too much air resistance through the system. It might be impacting your comfort right now. It might also be damaging your system and causing issues which will mean premature component failure.

We better find out what is happening and if any of the related issues are impacting you.

Resistance in a ducting system is measured in inches of water column – in. WC This is a bit esoteric and quaint to the profession, but we can live with this. The static drop over a conventional air distribution system is .4 to .5 inches.

There is a necessary pressure drop from the fan motor blowing out into the supply ducting to the return air duct at the air handler. This static pressure across the system is the accumulated effect of the duct design… Professional design here would follow from Manual D as formulated by ASHRAE – American Society of Heating, Refrigerating and Air-Conditioning Engineers and accepted by the ACCA- The Air Conditioning Contractors of America.

A well air distribution system designed to such standards with the static pressure in the range of .4 o .5 in. WC would perform well with components that are well matched and configured properly.

But a variety of things can upset this pressure balance.
First, we must understand that not all central air distribution systems have been designed with Manual D. Your system has a designed static pressure, more or less, depending on its history.

If your system is under the care of an HVAC service company, they have a sense of the proper pressures for your system according to the manufacturer’s specifications for your component system. You do have a maintenance agreement? Here are more reasons why?

Related: Duct caveat here… Oh and other parts of the ducting system can leak and reduce global resistance, causing additional problems, but not really solve the problem with air resistance. Duct leaks are quite harmful in themselves. Make sure you are are aware of these fundamental issues, but that is a separate theme and a separate story. More on the issues with duct leaks here LINK

When the components through which air must move, create too large a local or global air resistance, this global pressure drop impacts the function of the entire system. Air resistance impacting the proper pressure drop can leave you in discomfort. Greater resistance and your components can be damaged causing premature failure and unnecessary expense. We will talk about what can happen after we look at the effects which can upset the proper static pressure with excesslive added air resistance.

Let’s look at filters first.
There are a couple critical issues which can arise around your filtration system.

The system was designed with a filter system in place. It might have been a simple fiberglass filter intended to protect the internal components from contamination and airborne debris. So you or someone else just might decide that little crappy filter is not filtering well enough and find a better filter that traps finer particles. This is a big deal. We talk about selecting filters here in more detail LINK, but here we are just discussing the pressure aspects.

There are also issues with getting and installing proper filters. Everyone wants good clean indoor air. So it would make intuitive sense to put denser, higher MERV rated filters into the filter tray of your home. We talk about filter types and their ability to filter here. LINK.
But the wrong filter in the wrong filter tray of a susceptible heating and cooling system, can upset the pressure balance and create these same issues with inadequate pressure drop across the system and the emergence of issues related to poor air flow. We talk about finding the right filters to suit your needs here. LINK

If a filter with a pressure drop of 0.25 is used in an air handler, the filter alone can use half of the system’s available static pressure. If a high MERV filter is installed without designing for it and the static pressure is increased to an amount much higher than the optimum, several negative consequences can result.

The second critical issue with filters is the ignored filter. It gradually fills up with crud and the air resistance can go up enough to upset the balance of airflow. It first affects your comfort and then impacts your components. When is the last time you saw your furnace filter? LINK

Restricted air flow, i.e. abnormally high static pressure, can have a devastating effect on your heating and cooling components.

To understand the possible impacts we must also understand how the types of motors in our HVAC system will react to an increase in static pressure.

Do you know what kinds of motors you have? The traditional motor is an analog PSC – permanent split capacitor motor. It will come on and run up to a set speed. You might also have ECM motors in our system and they are more flexible on speed and torque and are driven by controllers to deliver a set volume of air. We go into great detail about comfort and saving money and the relationship of these issues with motor choice here. LINK

Here we are only interested in how each of these motors reacts to increased back pressure in the duct system.

The effects depend on the motor. An ECM is programmed to deliver a quality of air per minute. If the static pressure goes up, the ECM motor ups its speed and torque trying to drive the proper amount of air through the restricted air passages. Pressure in the system might increased to 1 in. WC – double the pressure.

The ECM will strain to its limits which would be heat sensors cutting off current to the fan. Continuing to push the upper limits of power used in the ECM will limit it life, and the right amount of air will not reach the system when it is needed. THe ECM will use a lot of power trying to push air where it cannot.

The PSC motor acts completely different. A PSC blower motor will work up to about 0.5 in. WC, then it will “fall off” i.e., the motor will stop pushing, although the fan will continue to turn.

The ECM, while most efficient at 0.3 inches of static pressure, will continue to work up to about 1 in WC, and this just might be enough to collapse your overfilled filter causing it to collapse and quite filtering at all. This can allow gunk into your system which can gum up your evaporator coil and prevent proper exchange of energy across it. This is where the cool is generated. PSC motors can also collapse a dirty filter also, but less so than an ECM. This can also gum up your blower motor and create more problems.

This conversation about abnormally high pressure in your heating and air conditioning system segues right into what high static pressure can do to your system.

As the air slows down in the ducts, during a heating season, the slow moving air could actually cool, reach dew point and create mold in the duct or mold at the register. This is also exacerbated by problems with poorly insulated ducts, slow moving air in warm ducts while traversing a cold unconditioned environment like an unheated attic or crawlspace could be a key to a mold growth and exposure to allergens generated right in the heating and cooling system.

Static pressures can go on up from here if the situation is not mitigated.
Abnormally high static pressure can choke off air flow so severely that your evaporator coil can freeze up and create frost out the refrigerant lines and freeze up and destroy compressors in the outdoor unit. We discuss this particular issue in detail here. LINK

Do you have a gas furnace? or a furnace powered by any other fossil fuel? THe heat from a furnace funnels through a heat exchanger on the way to the flue. A lack of proper airflow across a furnace heat exchanger can can cause the heat exchanger to crack prematurely. More on heat exchangers here. LINK

Other issues can impact your static pressure.
It is not a good idea to close of the vent in that unused bedroom. You are increasing the static pressure and setting any number of critical parameters out of balance. Lots of good reasons not to close off ducting. More on that subject here. LINK

Flexible ducts need to be stretched out and put in tension to operate properly. Has someone been in the attic and smashed a duct? Things happen. It is best to know what is happening in the attic. LINK

And then object placed in from of supply duct registers can restrict flow and create excessive back pressure. And cold air returns are such a big factor here also, and in so many ways that can create a problem. Make sure you check out the variety of issues around possible duct defects as part of your analysis to understrand what is happening within your air distribution system. LINK

In conclusion:
Abnormally high static pressure in your HVAC system is quite serious. Make sure the filters you are using in your system are not bollixing up your efficiency or worse. The dollars you save are yours to keep, or spend frivolously, elsewhere.

And don’t let pressure issues actually muck up you level of comfort.

Clogged filters are a big deal make sure you have a plan to change them on a schedule. LINK
Proper maintenance and close communication with an HVAC service company you trust is essential. You will save money, and never know how many times you headed off a disaster with loss of conditioned air. That is the trick of it. You cannot add up money you save, you can only complain later about the money you have to spend. in an emergency.

Any questions? Any comment? Feel free to add them in below. I you feel this info is useful, please share it. You might save someone from unnecessary expenses.

When was the Last Time you saw your HVAC filters?

Air filters in your heating and air conditioner system are easy to forget. When is the last time you have seen them?

Air filters, depending on the MERV rating which fits more into a discussion of how well you want your air filtered, LINK  are critical to the proper performance of your HVAC system.

Clogged up filters can impact your comfort and damage the components of your HVAC system. Maybe it would be appropriate to go check on them now, and if the are seriously clogged, figure out a new system for making sure the heating and cooling system filters are changed on a regular basis.

What kinds of problems can clogged filters cause?

Clean filters protect our Air Handler components from damage. Your blower fan runs more efficiently when not incumbered by contaminants. Your evaporator coil exchanges heat much more readily when its surface are debris free. A contaminated evaporator coil can cause system imbalance and freezing which can destroy compressors while not keeping you cool LINK and clogged evaporators can allow the growth of mold and make your whole house smell like dirty socks or worse.

Dirty filters gradually increase your system’s back pressure which in progressive stages, can
first increase your discomfort, reduce your flow of conditioned air and eventually destroy the ability of your system to work. Low air flow can cause your system to freeze up again the link on frozen systems LINK but also cause your combustion chamber to crack- do you have a gas furnace with a combustion changer? LINK

Poor air circulation through a combustion chamber allows excessive heat to impact the shell of the chamber and stress it excessively. Repeated stresses eventually will crack or allow the combustion change to corrode, Porosity in the combustion changer can cause fires and potentially contamination of the indoor air with carbon monoxide.

So clean filters are essential to safe and efficient operation of your heating and cooling unit.

Clogged fillers can also create extra pressure  on a clogged filter and with the changed air temperature dynamic in the air handler allow water to condense in the clogged filter and cause the clogged filter to collapse and allow the contaminants in the cold return air to bypass the filter and just steam into your system and coat the evaporator coil with crap and allow crap to collect on the blower motor. You don’t want this to happen either. You prevent these expensive problems from occurring by replacing your air filters on a regular basis.

Clogged filters cause just plain old mundane problems.

Ignored filters creating back pressure can make you miserable by impacting the ability of your system to generate cool or heat as you need it for comfort. Dirty filters can combine with other factors that impact your mechanical system that impedes system balance and create an area of your home leaving you too warm or too hot or just feeling distracted with discomfort.

A dirty, clogged filter can dramatically reduce air flow. A reduced air flow increases furnace and cooling system run time, which increases wear and tear, while your energy consumption- your electrical bill, goes up. Your comfort level is also diminishing. And then the system can break.
Filters can become moldy and wet, and collapse and not be filtering your air at all. This can allow your evaporator coil to crap up and be inefficient and create conditions that can stink up the whole house. LINK
When the air stops flowing, systems can freeze up. LINK

When insufficient air flows through and around your heat exchanger, you can damage it. LINK
Your filters will get timely attention or they will get attention after a more serious problem develops.

If it has been a long time, or some unknown period of time; well, get up out of your chair right now and go check your HVAC filter. Take a picture of it with your smartphone and share it here. People need to be reminded that important stuff like filters can easily be overlooked in the rush of each day…

Filters play 2 critical roles.
They protect our equipment from damaging contamination.
At a minimum your HVAC filters play a key role in how well your HVAC is functioning.
For optimum operation of both the filter and the HVAC equipment, the filters should be replaced or cleaned frequently.The light fiberglass filter that is standard keeps crap out of the mechanics of your system. Like protecting your wet evaporator coils from being covered with wet stuff and losing it ability to keep you cool, or messing up blower motors which work better without detris in the moving parts. We talk about protecting the innards of your air handler here on another key issue, making sure your air return ducts and filter assembly structure is airtight and not bypassing air around the filter.

Secondly, the level of filtration you want in your home to protect your air from mold spores or fine particles, or… depends on proper services of the filtering medium. The length of time between attention to filter installations depends on your chosen filter type.

So what do we have to do to get on top of this Filtration Issue for good?

Of course, you know this, and you have the correct date to next change the filters stored in your smartphone, or written on your calendar… Your filters need to be replaced or cleaned on a regular basis, for your best health, for the proper operation of your cooling and heating equipment.

And, of course, you have a supply of replacement filters in your home, and the replacement filters are the exact size that fits perfectly into your filter box. Poorly fitting filters and leaky return air ducting are a problem ready to happen, but a separate problem we discuss here. LINK

So what can we do to not forget our filters? Oh, and remember what kind fo filters we need?
rewrite –
We suggest putting a note in your phone with filter size so you don’t have to check it each time you are ready for refills. Also, many of the thicker filters have a “nominal” size which is slightly different than the actual dimensions of the filter. Some filters state the actual size on the side, while others just list the nominal size. Unless you are replacing with exactly the same manufacturer’s nominal size filter, It’s best to confirm that any replacement filter is also the correct actual size.

Your filters should be easy to replace with proper instructions available right where you are replacing filters.

Related Topics
Who is watching out for your elderly parents when it comes to home maintenance and safety issues? LINK
Would you rather have someone watching out for your HVAC filters for you?

[image needed plus infographic] So then how long has it been since you saw your HVAC filters?
If you can’t remember, you probably should go check on them.

Filters with higher MERV (Minimum Efficiency Reporting Value) ratings of MERV 6 or above can trap pollutants like pollen, dust mites, and mold spores.
Images needed – Image captions.

What kind of filters does your system need?
How often are they to be changed?
Dirty filters filter well, too well… until they collapse.

HVAC Electric Motors Matter to your Comfort and your Wallet. Here is why.

Motors in HVAC components have a direct bearing on your comfort and on how much you pay for heating and cooling. Therefore, it is essential that you know a little something about these types of motors. We will concentrate in this discussion more on fan motors for air handlers, but the same themes also play out for compressor motors and motors associated with modulating furnaces.

Let’s make sure we know why we should care

The choice of motor driven components relates to how comfortable you are in your home, the quality of your indoor air, and the ability of your HVAC system to serve you with the nuanced services you need to be happy, comfortable and frugal… or frugalesque. Motor choice can save you money.

Heating and Cooling Components encompassing ECM motors can cost 40% more – more or less and components are always a major investment. And salespeople will manipulate you and your aversion to spending a penny you don’t need to spend, and maybe manipulate you into a less beneficial solution.

So you need to know the fundamentals here. The point being made is that the extra upfront cost of components with ECM motors are a good investment in saving money and being more comfortable.

There is an important aside here: ECM and PSC motors  react differently to static pressure problems n your heating and cooling system. Problems with static pressure, air movement constraints-  are a fundamental issue that we deal with separately. here. LINK

There are two critical factors that make electronic commutated motors a much better investment than the traditional PSC motor even though the PSC motors are less expensive up front.

ECM motors save you money, but let’s talk about the comfort advantages of variable speeds, first.

First, ECM motors can vary their RPM by controlling the pulse waves of current. This allows important variability in how much conditioned air or just circulating air is being driven through the system.
Traditionally, PSC motors were single speed. This is what most heating and air conditioning systems have if you have not upgraded in 10 years, or you are proud of your 20 year old furnace. The blower comes on full blast until the thermostat senses enough temperature and the fan cuts out as soon as the heating or cooling cycling ends. You may notice a pattern of being quite toasty and then feeling a draft when the heated air quickly dies off. These are the ups and downs of temperature as created by a one speed PSC motor.
Check out the image below.

Caveat on Saving Money with ECM Motors

ECM motors, and we will explain the electrically modulated motor in detail separately– ECM motors like every other component in the system, depend on all other components to be working effectively. Ignored problems in air distribution, poor filter selection or clogged filters, kinked flex duct, problems with cold air return patterns can actually cause your electric bill with new ECM motors to go up, because ECM motors are programed to move a certain volume of air and will strain themselves using extra power, to move the air quantities the system calls for.

Static pressure properly balanced throughout the system is essential to saving energy and being comfortable. We will go into more detail later, but PSC analog motors don’t use any more power because they just move less and less air as the system static pressure increases. Static Pressures across your air distribution systems are critical. LINK Again, we will explain permanent split capacitor motors separately, but the fundamental caveat needed to be shared up front. More on the costly travesties of defects in duct systems here. End of caveat.

To compete in the market with competitive pricing, PSC motors are often connected up in multi-speed variations using circuitry to change the analog dynamics of the permanent split capacitor motor. Multi-speed here means a single speed for various types of conditions; one speed for heating, another speed for cooling; a special speed for just air circulation. These are set speed settings but when viewed at a heat and cooling system, these are thought of as multi-speed units.  We showed a multi-speed PSC schematic earlier.

But ECM motors allow much more flexibility and comfort to your home, and this really helps with our fickle North Texas weather that can have us heating in the morning and cooling in the afternoon. And you don’t really need a lot of heating as the day warms and you don’t really need a lot of cooling as the day cools, just enough, not a full blast boost of heat or cooling. ECM fan motors can make a real comfort improvement for North Texans.

Let’s talk about how these variable speed advantages can impact your comfort.

With true variable speeds, your system can dial in the amount of cooling and heating to modulate your home environment to the needs you are experiencing. While a single stage system is pushing up the temperature to maybe you are too warm and then cuts off until the temp cools to the set point and by then you might be chilled. A true variable speed system can deliver just enough heating or cooling to maintain an even and comfortable temperature in your home. Now what is that worth in comfort?

temp changes over time illustrated

No one deserves to be tortured by full blast heating with wide temperature fluctuations.

There is also a noise advantage.

The ability of ECMs to ramp up and ramp down slowly adds to their quiet operation. And of course, all this smooth ramping of speeds is much easier on switches, even a “small” 200% current surge from a PSC motor to ramp up speed is a jolt to the system. Anybody have an ratcheting breakers when the A/C comes on? It happens. A lot. Do you hear your heating or cooling system come on? Does it annoy you? Does it wake you up at night? Here is a solution to discover, next time you are making upgrade decisions. LINK

We have issues with humidity in North Texas. The size of your issue with humidity is a direct function of how much air leaks into your home and how well you home handles the moisture the human inside generate. This is an important but separate issue discussed here. You do realize that the humidity of the air in your home has a huge impact on air quality?

In our seasonably humid climate here in North Texas, ECM motors can be programmed to run slower and cool slower, when appropriate, to better handle the latent heat generated by condensing moisture in your evaporator coil, as compared to rapid cooling and the system cuts off and leaves you feeling muggy because the cool temperatures have been achieved but too much moisture has been left in the air. Too many people have too big an A/C because most people think more comfort is a function of more cooling power. This is not true and, and too big can work against you. We talk about too big here.

Using ECM motors and the right controlling systems, humidity levels can be set at a precise range and the system with dehumidify as needed to keep you in a safe and comfortable state. We always need to control for moisture at the sources as described in the above links, but precise control of humidity can really keep you comfortable by making sure the conditions for comfort are in your home, before your body and brain start whispering to you that you are not comfortable.

Is proper air filtration important to you? How often is your filtration system working? When the heating or the air conditioning is occurring? Or are we running a system full blast in air circulation mode and running up the electrical bill?

Now many of us like clean indoor air and use filtration systems to help clean the air. We discuss Filtration here in depth. LINK but if your system is not moving air, there is no filtration going on. Variable speeds allow circulation stages that allow constant filtration to a level needed, and saves you money.

Analog one speed systems set on air circulation, are loud and expensive to keep on at all hours, and without considerable system control you are manually selected whether you are heating, or cooling or circulating air. These particular aggravations are determined by your own system you live with. These are what you consider when you go through the process of evaluating new investments in heating and cooling components. We discuss the wide spectrum of issues to consider in a major upgrade here. LINK

Let’s pause and look at another critical difference in PSC and ECM motors. They each respond differently to changes in the static pressure in the system.

Static pressure is the basic resistance of the air passages in any particular air distribution system. The basic static pressure system is set up by the installation contractor. So many tons of conditioned air equals a cross section of the ducting system and the speed of the air in circulation. The speed of the PSC motor is set according to design and the system works and the system provided the prescribed airflow.

Comment: This is a bit theoretical to make the point which is coming, but there is much less duct design and attention to ducting during upgrades to major components than one would wish for, and this is a not good. This is not an abstract issue, but depends on the situation in your own home. We discuss possible mechanical defects that can impact and erode performance here. We mentioned defects like this can cause your ECM motors to run hard and fast and not save you money. Well all kinds of comfort problems, and issues which strain and destroy your heating and cooling components prematurely, start with ducting defects. Make sure you check these issues out. You will not be comfortable, you will be tossing money into the disposal, until these issues are diagnosed and solved.

Back on point – with PCS motors, a change in static pressure- a dirty filter can reduce air flow; or human disruption of the return air system, or a very wet evaporator coil, can impact the static pressure, and reduce the actual air flow. PCS motors run just fine at rated speed, but air is not moving as well as the static pressure increased. Your air flow can be choked down, until your system can actually freeze up which is not good. Low are flow can also starve your furnace heat exchanger and cause serious damage. Other issues can arise. Pressure issues in HVAC systems is discussed here.LINK Have you changed your filters lately? This is a big deal. LINK

On the other hand, DCM motors are programmed to deliver a given quantity of air through the system and will increase in velocity and effort to push through changes in static pressure. They can actually push so hard as to damage the motors- denature a permanent magnet or melt insulation on wiring in the motor… ECM motors can actually deform a clogged filter pushing on it and then all the crap just bypasses the filter… money, money, money.

The point here is that we need to be aware of problems which can impact the static pressure in the system and that all components are impacted, each in different ways. If you hear your blower motor sounding strained, check out what is happening. If you seem to be lacking air flow in the system, this is a sign of a static problem. Depending on the motor types you have in your system.

Secondly, we need to talk about actually saving you money.

You are paying more up front, how are you going to get your money back. Actually, the payback period is short. About 3 years. This is a generalization, of course, what is important to you is what is happening at your home.

If you want to run your filtration system all the time, you will save even more money. A typical PSC motor running all the time can use 500 watts or more, while an ECM would run less than 100 watts. The ECM motor is adjusting its speed and effort as the system calls for services. We do remember what the PSC motor is doing. Running full blast at rated speed.

If you have a mechanical system to drive out stale air and bring in filtered outside air- I am describing a mechanical ventilation system, you will save more money. More on mechanical ventilation here. LINK Where is your fresh indoor air coming from when the doors and windows are closed? Worth thinking about. LINK

ECM motors are just more efficient. They are about 80% efficient as compared to PSC motors approach 60% efficiency. Efficiency here means electrical energy doing the good work and just not creating heat. The precision of the commutation and the lack of friction just basically save you money every time the system comes on.

Miscellaneous Advantages of ECMs over PSC Motors.

A Comparison list between PSC motors and ECM

This useful diagram swiped from the Dept of Energy.

The elimination of the sliding contact between brushes and armatures allows brushless motors to have less friction and longer life. The working life of an ECM motor is basically limited by the lifetime of their bearings.

Brushed DC motors- the PSC motor in our discussion- develop maximum torque when stationary, linearly decreasing as velocity increases. Electronically commutated motors- ECM motors, can create as much torque as needed (within design limits)  at whatever speed is desired because the controller system is dictating the driving currents whereas, an analog electrical motor with brushes is using the reactance of the circuit created by the analog design to control speed and torque using the natural electrical physics of the capacitor and inductor components and in relation to the load on the motor.

Brushless motors are more efficient. Higher torque to weight, higher torque per watt, which is what you pay for each month measured in kilowatts. Electronic commutation allows more precision to the electrical currents and more efficiently applies the torque developed. You also have no friction losses from the brushes dragging on the armature.

Brushless motors are more reliable. There is no erosion of the brushes because there are no brushes. The components are cooled by being attached to the shell of the motor and do not need airflow for cooling; therefore, brushless motors can be enclosed and kept clean.

Components using ECM motors are the future.

PSC motors are the legacy systems which hang on because it is what people are used to, and quite frankly, I do not have to tell you the power of saving a buck right now.

But I have laid out a case in much detail, maybe even too much detail for investing in ECM motors. There are other benefits to using ECM motors in compressors, in furnaces, but this story has carried on too long already.

Make sure you figure out how to best increase your wealth of time rather than save a buck right now. Save bucks right now by not ordering pizza out. Save for the future by saving money day in and day out.

Any questions? Any comments? Anybody want to add their two cents. Feel free.

Are You Paying Proper Attention to Your Condenser Unit

Condenser coils play a critical role in your air conditioner’s cooling system. Yet they are fraught with risk. We need to pay attention to our condenser coils. Let’s take a closer look. Literally.

Have you seen your condenser lately? Is it sitting on a nice even concrete of stone pad? Or are bushes encroaching on it? Of course, it isn’t or you have an immediate repair task at hand. Otherwise, I hope you have an Air Conditioning and Heating Maintenance contract, and are holding a qualified HVAC service company responsible for your HVAC system. In this specific case, it revolves around keeping your air conditioning coils clean and protecting your heating and air conditioning system.

The condenser coils are where your cooling system casts off heat from your home into the outdoors. Your A/C outdoor unit is built like a tower with a powerful fan at the very top which draws air up and out of the outdoor unit. Around the edges are arrayed your condenser coils. This fan creates negative pressure in the outdoor unit that sucks in ambient air through the sides of the Air Conditioner, and across the condenser coils.

This is a typical Condensing Unit. The lawn is nicely clipped and there is a nice concrete pad. No weeds, or bushes, or vines are intertwined. But we should wonder WHAT is inside on the air conditioning condensing coils impeding air flow.

The coils dissipate the heat created in changing the state of your refrigerant back to a liquid. Therefore, condenser coils need clean surfaces and open airway passages to more easily allow the heat in the coils to radiate and conduct heat away and allow the refrigerant to return to a liquid state, where it will be returned under pressure to the air handler inside the house where the refrigerant will again be expanded into gas in the evaporator coils and effectively strip your home of the energy to do this. Any questions here? check out the notes on the thermodynamics of a heat pump just below.

Here is an easy understood diagram and a clear explanation on the heat pump cycle.
You might know it from school as the Carnot cycle, or the refrigeration cycle. But the Principles of Thermodynamics allow us to leverage the phase change of refrigerants so that we can economically extract heat from your home, and deposit it out of doors. This page details and explains how this works within the components of your Air Conditioning system.  

What is phase change and why should I care?
Phase change in the refrigerant in your AC system is what keeps you cool in summer. Yes, it is that important. Like life saving. Do you want to know more?

A key factor here is hot weather, the hotter the weather the bigger the effort needed to dissipate heat. Temperature differential aids this process, the bigger the easier. Therefore, any issue with coils dissipating heat well will be most acute on the hottest days.

Because those coils are located outside, they are susceptible to dirt and fuzz and crap buildup over time. All kinds of things can foul a condenser coil here in North Texas. Living near a major arterial can just put a lot of dirt in the air. We live in a virtual garden of Eden in North Texas, and flowering trees and bushes and wildflowers can put off pollens and blossom fragments, and the North Texas winds will carry them around our neighborhoods. If you coils aren’t kept clean, your air conditioner can encounter some very serious problems. And we understand these problems are most acute on the hottest days.


image despicts a fuzz filled, dirty condensing coil assembly.

Fuzz filled condenser coil assembly is seriously impacted. Make sure this is not happening to your outside air conditioning unit.

Dirty coils can impact you in several ways.

You might be less comfortable because dirty coils cause the system to be out of regulation and not cooling as effectively as the system can when in tolerance. If you are not as comfortable as you would like to be, dirty coils could be contributing to your misery. Longer run times, less ability to deal with humidity; several issues which directly impact your comfort could be caused by dirty coils.

Nobody likes to pay high energy bills, and a dirty coil will cause your system to work harder to make you comfortable and working hard in mechanical systems means using more electrical energy.

Dirty coils stress the compressor in the outside A/C unit and stress is what causes premature failures. But heating and cooling is all one system and one major component not performing properly can stress all other components.All components are under stress. Stress causes premature wear and early failure. Failure can leave you without cool on the hottest days. Therefore we want our coils clean and our system in top running order.

So now we know why we want our condenser coils clean. Now let’s look at two issues to resolve about keeping them clean.

The simplest way to keep your Air Conditioning condensing coils clean is to have a maintenance agreement with a reputable Heating and Air Conditioning Service Company and have them checking on and cleaning your condenser coils on a regular basis.

However, there are unusual cases where your condenser coils could use even more attention. Many of us live in tree lined neighborhoods or out in the wild with the poplars. We have so many variety of trees and flowering bushes here in North texas and this can create an unusual problem for an outside air conditioning unit.

A flourishing burst of pollen or blowing blossoms have encapsulated more than one outdoor air conditioning unit and caused a failure. You do not want to face this issue, you don’t want to experience loss of cooling. You do not want to face the smack to your wallet.

Do you live in such an area?

You might need to take special precautions on your own  to make sure an acute problem does not occur outside of the regular maintenance cycle. There are special options you can consider. There are sensor systems which can tell you when your systems are being stressed and will notify your HVAC service company of a problem. Or you can just be aware of these issues and in the spring, just have an extra eye out for problems here.

Being aware of the possibility is an important step in making sure such a dismal event does not happen to you.

Any questions or comments? Who has an experience to mention? Who has a recommendation? Add your thoughts in the comment section.

How long has it been since your Combustion chamber has been inspected?

The days are still warm when this was written, but what is critical is the date you read this. Do you use natural gas or propane to heat your home? Fall is coming, and this means you should be hearing from the HVAC service company you trust. You do have a HVAC maintenance agreement don’t you? Having your combustion chamber checked on a regular basis is a quite good reason to have one.

Burning fossil fuels creates carbon monoxide as a byproduct. Carbon monoxide in the air is deadly to living creatures. Burning gas means you have a combustion chamber and a heat exchanger to add heat to your air stream. This air stream is then blown out through your ducted system and out through your home to make you warm and toasty and cozy on the coldest day. You do not want carbon monoxide mixed into this air stream.

Here is a reminder that all of us using furnaces for heat, we are at risk from carbon monoxide poisoning. As long as we like living within draft-free shelters and want to use combustion to heat our homes, we are at risk.

More than one HVAC service company has been asked to verify the proper operation of an HVAC system in a home for sale by a home inspector and discovered that a combustion chamber was dangerously defective. Leaks and corrosion have been found many times, meaning the existing owner and her family had been exposed to dangerous CO.

Leaking combustion chambers need immediate replacing. Combustion gas leaks are not something you plan to deal with later. Needless to say, The home buyer would be quite relieved in this discovery situation and the homeowner should be quite appalled.  The point here is- if you have been coasting for a long period of time without careful attention to your combustion chamber, please schedule some heating and cooling system maintenance.

When furnaces are working properly, carbon monoxide bi-products go right up the chimney and out of doors where they dissipate. Problems arise when combustion chambers crack or corrode. Combustion chamber porosity allows the carbon monoxide to leak and mix into the air circulation system of your home.

The Carbon Monoxide is slightly lighter than healthy air and will thus distribute right into the life sustaining air in your home. The carbon monoxide is odorless, tasteless and not detectable by the human body. It simply enters the lungs, absorbs into the bloodstream and destroys the ability of red blood cells to absorb oxygen.

In a high enough concentration, victims die of carbon monoxide poisoning unless rescued. Vomiting and nausea and chest pains are symptoms of carbon monoxide poisoning. Low chronic levels of carbon monoxide, while not deadly, can create chronic symptoms of ill health. Elderly folks and infants are most susceptible.

Make sure you know the symptoms of carbon monoxide poisoning. Small background amounts can make people sick and sap health. I have an old friend in Arlington, Texas, who decades ago experienced a long bout of illnesses with her children. She was quite unnerved. When carbon monoxide was finally diagnosed as the culprit, she pulled out the gas furnace and went all electric.

Now, who was going to tell her that was a bit of an overreaction? Regular attention to the furnace could have made a difference. There are quite effective carbon monoxide detectors, if you know what you are looking for. The link above also talks about detection of carbon monoxide in your air. The Center for Disease Control has great info on Carbon Monoxide poisoning.

There are other potential sources of carbon monoxide in your home.

Make sure you know them and make sure you understand the concept of negative pressure inside your home.

The risk of CO from your furnace is preventable with an annual Fall Heating System inspection. A Fall inspection confirms your combustion chamber is sound.

Combustion Chambers are under severe Mechanical Stress. They do not fail at random.

There are 2 significant destructive forces acting here.

First, lets look at thermal stresses.

Fuel burns and the metal chamber expands as it is heated. The stress of expansion acts at joints and curves and connections. These stresses, acting 1000s of time in any one heating season and adding up over a period of years, can crack the combustion chamber. Units over 10 years old are even more at risk. HVAC manufacturers work very hard to make reliable combustion chambers, but maybe one in a thousand has a small undetected defect where problems can take root.

Now we need to discuss high humidity and corrosion.

As heating units have become more efficient over the years, the risk of corrosion has increased. As HVAC efficiency has increased, flue temperatures decrease. Less heat is wasted up the flue hence the system is more efficient. As exhaust gas temperatures decrease, the humidity in the system increases, and there are more encounters with condensation in the system. When condensation occurs in your flue, carbolic acid is formed from the chemical brew of combustion. Carbolic acid is very corrosive.

In conclusion, an HVAC Maintenance Plan makes sense for you, particularly if you are using natural gas or propane.  HVAC service companies  like to inspect Heating and Air Conditioning units in the Spring and the Fall. A spring maintenance inspection helps make sure the summer cooling will be done efficiently without undue wear and tear on the system.

But the Fall maintenance inspection is the most critical. Sure we want the furnace working efficiently. Sure, we want your furnace to come on when you need heat. But nothing is more critical than insuring a catastrophic combustion chamber failure has not occurred. We discuss whether an Heating and Air Conditioning Maintenance Agreement makes sense for you here.

We also recommend Carbon Monoxide Detectors. Of course, detectors are not infallible. Please keep the batteries replaced. The Center for Disease Prevention suggests changing the batteries when Daylight time changes in the Spring and Fall. Do not depend on detectors to cover for neglecting the regular inspection of your combustion chamber. Both are critical. More on carbon monoxide and CO detectors here.

Have you ever experienced a Carbon Monoxide problem in your furnace? Please add your comments below. Your experiences might help someone else better understand the risk of Carbon Monoxide.
Be safe. Get your HVAC unit inspected at least every Fall. Share this post with your friends. Lets watch out and protect each other.

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