Your HVAC Duct System Plays a Crucial Role in HVAC performance.

If your home has a ducted heating and Air Conditioning system, the layout and quality of the ducting plays a crucial role in your level of comfort and in the quality of the air in your home. Ducting systems are often ignored in conversations with service providers. It is typical for HVAC service people  to ignore ducting issues and, instead, turn to your central HVAC unit as the solution to the issues you describe.

And way too many conversations around HVAC issues take place with you either shivering in the cold or sweltering in the heat with a broken system, and so the conversation centered around immediate issues, and whether the Central unit can be repaired or needs replacing. We need to move away from this conversation pattern because, in this scenario, the ducting system would appear not important; when in fact, it is important and might have played a key role in mechanical failures elsewhere. This is why a conversation about HVAC systems should take place at a more appropriate time of your choosing.

Do not take their indifference as a sign that all if fine with your ducts. Do take their attitude as a cautionary tale. These attitudes are out of date according to their own national association, the ACCA- Air Conditioning Contractors of America. No system will work properly without an effective system of air ducts.

What kinds of issues with your ducting system might you have?

Ducting issues are serious. Defective ducts can cause an effective working forced air- HVAC system to operate poorly. Duct problems can contribute to an unhealthy home. And duct problems can leave a room too hot or too cold. Lets explore what can go wrong with ducts and how it will impact your comfort level.

Any comprehensive conversation about HVAC issues must deal with structural issues- air leakage, insulation and solar heat gain issues.

 You and your HVAC service company should be talking about home performance and how the structural and mechanical components of your home work together as a system to make your home comfortable and healthy. The subject is home performance and how all the home’s components are a system working together to either help or hinder comfortable living and healthy air.  Home performance is defined here.  This conversation about home performance is a critical part of the conversation you need to have with your chosen  HVAC service contractor and should be a critical component in your selection process for the HVAC service contractor you are going to hire.

Imagine your cool air having to run a gauntlet through the hottest part of the house.

A huge proportion of ducts in North Texas are in the attic. Something like 70% of homes  in North Texas are on slabs with an air handler in the attic and supply ducts running around in the attic for distribution. The return ducting runs into the attic to connect to the air handler.

Quick question what is the very hottest portion of your home? If you guessed attic you are right. If you think it is somewhere else- get up in your attic some summer day. Really high temperatures.

The ducts are in the attic because it made construction easier and cheaper. Putting ducts in the attic raises your energy bill every month, but up front, it kept the price of homes lower (or the profit on the home higher) New green construction has new solutions for this issue. They are insulated at the underside of the roof deck and the attic becomes conditioned space and the problems with having ducts in the attic are nil.

Lets Detail some Specific Duct Issues

Supply ducts leak.

They leak at joints, elbows and connections. Air handlers have powerful fans and the pressure in the ducting pushes your conditioned air out into the attic. In the cooling season, this  is cool air intended to make you more comfortable. Instead it is making your attic a little cooler and your wallet a little lighter. In winter, the conditioned air- this time warm and toasty- is leaking  out but now it is leaking  out into a cold attic. This wastes energy again but now warm air condenses  on cold objects  creating conditions conducive to mold and mildew growth.

Leaky ducts in the attic create negative pressure inside your house to make up for the conditioned air leaking out in the attic.  This make up air comes in under the door, and around the window, and through the band joist etc. Hot humid air leaking in, in summer, raised the humidity level of your home. In winter, cold air leaks in and dries out your interior air. How many of you are running a humidifier in the winter? Ohh, my!  The issue is leaking air. Leaking air creates health and comfort issues. Make sure you understand the risks of air leaks here.

Unhealthy Moisture Levels allow biological pollutants like molds and mildews, to thrive...

Too much moisture in your home allows biological pollutant- mold and mildews and all the rest to flourish. Does your home seem musty or smell of mildew? Is the air in your home healthy? We explore the health of the air in your home here. [/stextbox]

Return air ducts suck. Leaky duct returns suck stuff in.

The return ducts are between the big intake grill inside your living space and the location of your air handler. Now I said earlier, that most homes in Texas have the air handler in the attic. Well, what really matters is in your home. Air handlers can also be in the garage or in a crawl space.

This return side is under negative static pressure- sucking like a straw and sucking up whatever is in the space the duct runs through. It might pick up some carbon Monoxide from anidling car in the garage- or maybe aromatics from paint thinners and pesticides stored in the garage. What kind of possum farts linger in the crawl space? What moldering critter in the crawl space helps with make up air in your home?

And then there is the attic. What kind of dust and sneeze material is floating around in your attic being sucked into your system through a leaky return vent into your attic? Duct leaking is a big deal.

related: Crawl spaces are a particularly serious problem in North Texas.”

We need to address moisture issues associated with leaking returns and leaky supply ducts.

A return duct can draw in moist hot air in summer- make sure you see the notes on humidity in North Texas in Summer… -LINK- and burden-even overpower your system as it tries to dehumidify your home. The opposite happens in winter. Your return ducts are sucking in dry cold air from the outside and making your home feel very dry as the humidity level drops below a comfortable humidity level.

In winter, leaks in a return duct can waste a lot of energy- heating cold air takes energy. As cold dry air inflitrates your home, you can sense you home is too dry.  Do you use a humidifier during the winter? Well, you home is leaking too much outside air in and unsetting the humidity level you want. Solve the leakage problem in winter and you are solving the fundamental issue of too much humidity in summer. Air Leakage issues are discussed here. -LINK-

Leaking supply ducts create negative pressure in your home. The air leaking out from your ducts must be made up by air leaking into the house elsewhere. In summer this is hot moist air which increases our heating load and the amount of latent energy your system must be rid of, to lower the humidity level in your home to a  comfortable and healthy level. We talk about humidity, and latent heat and phase changes here. This is critical information you need to understand. Too much moisture in your house is unhealthy.

We will address solutions below but we are still slogging through potential issues with your ducts and heating and air conditioning system.

The enire duct system  can have a severe air balance problem

Issues of comfort around the house are usually localized. Cold rooms, unbearably hot add-ons and bonus rooms. -LINK- Often these issues are caused by structural issues, which are discussed here, -LINL_ but often ducting issues creating severe air imbalance also play a key role.

Kinked or smashed ducts can limit airflow and constrain the ability of the air handler to deliver conditioned air. We talked about leaky supply ducts earlier. Supply ducts can be completely broken. This means some space is getting no conditioned air.

Ducts can also be poorly laid out. Supply ducts can be too long and tortuously placed in the attic space. Most of the North Texas homes see a lot of flexible ductwork- ducting which is easy to use but also easy to abuse. Flexible ducting must be placed in tension to spread out the duct walls and open up the air flow passages properly.  Sloppy placement can leave the ducts lying about- even coiled up with air flow restricted.

Ducts can be poorly placed onto the plenum -LINK back to diagrams – and create turbulence in the plenum. Turbulence is friction in air. Turbulence reduces the velocity and movement of air. All these factors can contribute or cause general or localized issues with your ducting that cannot be remedied by attention at the air handler.

Return ducts or the lack of them can contribute to a serious air balance problem.

Return air is the path for air to recirculate back to the air handler. The standard return air for separate rooms here in North Texas is usually a gap under the door. Supply lines push air in and the increase in pressure pushes air under the door into the next room and finally to the big return air grill attached to the ductwork connecting to the air handler. This can become increasingly  problematical as homes get larger and more spread out.

This is not a good plan from the start. Its only attribute is being cheap. But things can change for the worse. Occupants can in the interest of privacy or to cut down noise from a neighboring occupant- get into the habit of closing up the gap under the door.

Or you can change out carpeting for a fluffier higher lift version and cut down this gap. Maybe the occupant is a cleanliness nut who loves throw rugs and puts a small throw rug in front of the door. All these things shrink the size of the gap and decrease the balance of the air flow in the room for sure, but also for the whole house.

Do you hear doors ajar slamming when the heating system ramps up? This air pressure build up is a great sign of a system balance problem and the makings of a comfort or moisture problem.

So now the system fans are pushing against a pressure gradient and air is not moving unless the door opens briefly or while the room is not occupied… This is not good for the home, the equipment or the occupants.

The pressure goes up a bit- mostly your fans are just straining- these are low pressure units there is no danger of the room inflating… but more air is leaking out through your home’s envelope- bypassing light switch panels and ceiling fixtures and gaps under the stud plates…

The return air system really does need to be evaluated on a room to room basis because problems of poor air circulation can be answered right here. It must might pay to have some design work done on the return air system for better air balance for better moisture control and greater comfort.

We talk about solutions below  but we are still counting down the culprits of  poor mechanical performance. You never know which is contributing. You cannot afford healthwise and comfortwise to ignore any of them.

HVAC supply ducts can be poorly insulated

Conditioned air travels through long supply ducts. Are your supply ducts in your attic? We talked earlier about ducting systems in Texas usually being in the hotest part of the house- well, Here in North Texas, attic temperatures can rise to over 150 degrees in summer. If your conditioned air is traveling long distances in poorly insulated ducting in an attic at 150 F, the air spilling out on you will not be as cool as it should be- particularly if the air flow is constricted and flowing poorly. We talk about constrictions and air flow issues earlier.

Poorly insulated supply ducts with restricted air flow not only keep you from getting properly conditioned air in quantities to make you comfortable but also can create serious moisture problems. You might want to gain some perspective on the physical properties of moisture

In winter, poorly insulated ducts in your attic allow your warm and toasty air leaving the air handler and plenum to be cooled down by an attic ambient temp near outside temperature. Besides making your heated air in your portion of the house feel too cool for your comfort- but you can reach 100% humidity and condense moisture on a cold section of ducting.

Moisture creates the conditions for mold to grow. Mold produces spores and you have a biological pollutant in your home that can make you sick

Does Your Home have any mystery ducting?

Many older homes were built before central air systems dominated the market. All kinds of retrofit gimmicks have been used in the past to distribute air. Air channeled through panned joist bays- joints bays turned into ducts with a piece of sheet metal placed over the the bay- works poorly in the best of conditions, but if the bay is in unconditioned space- like a crawl space- this is an area zoned for mold and mildew.

Remodeling can create mystery ducting

Remodeling can often concentrate on the beautiful and the added space, and rather overlook issues of substance. Duct design is often done by a guy with tin snips and duct parts purchased from the big box store. A poor patchwork mechanical system to an add-on or an addition can leave you miserable. We discucs issues with remodeling and remodelers here;  but things can get moved to make room for change and the stuff moved can be broken in the process.

When home inspectors and HERS raters go camping they sit around and tell horror stories about ducts. They don’t need Stephen King stories to stand people’s hair on end. Did you skip the article on crawl space issues?

Ducts are a huge issue in home and often get overlooked when people are looking to solve comfort issues. Do not be one of these homeowners. Make sure your HVAC service company brings up these issues or you do it yourself. Your comfort and health are both at stake.

Feel free to add your thoughts below. Any questions? Any stories? Great!