The Air Exchange

When you hear the term Air Exchange what comes to mind? Some picture a place like where you exchange your gas grill propane tank, some think of a returns department. Even those who have heard the term sometimes don’t fully understand what it really is. 

On the surface air exchange is a fairly simple concept. Taking the air inside your home and replacing it (or exchanging it) with fresh outdoor air. Not all that difficult to understand. The complexity comes in on how that is done. Lets first get an understanding of what an air exchange is.

Air Exchange is the number of times the air inside your home is replaced with fresh outdoor air. The American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAR) recommends at least an air exchange every 3 hours. Exchanging air is typically done by having a continuous source of fresh air coming into the home while exhausting the stale air out. So far everything still seems fairly straightforward. Good air in, bad air out – easy. The challenge comes in calculating exactly how much. Bringing too much in and you put unneeded stress on your HVAC system. Not brining enough in and now your indoor air quality suffers. Here is where we need to do a little math. Not to worry, this is fairly simple math. If you have a 1,000 square foot home with 8-foot ceilings you have approximately 8,000 cubic feet of air in your house. Exchanging the air once every 3 hours will mean that you need to move about 2,700 cubic feet of air an hour. Now divide that by 60 (60 minutes in an hour) and you get approximately 45 cubic feet per minute (CFM).  That would be for a home that has zero natural air infiltration. To get a better picture of how much air is actually needed, we need to look at different types of homes.

Older, drafty home. If you have an older home that has drafts, the good news and the bad news is the same news. The good is that you have a natural flow of fresh air coming into your home. Engineers call this natural air infiltration – the rest of the world calls this a draft. The bad part of a drafty home is that you have no way of controlling the air and your utility bills are probably high. For these types of homes it is important that you are properly ventilating the home with bathroom exhaust fans and a kitchen range hood but typically you do not need any additional equipment to ensure fresh air is coming in. The amount of air coming in is going to naturally “push” the stale indoor air out. Adding insulation, sealing doors and windows and so forth can reduce the amount of drafts, which is a good thing, but keep in mind that you may need to add a mechanical solution to bring fresh air in.

The Goldilocks House. Not too drafty but not too tight. These homes are typically a few years old (10 to 20) or an older home that has been renovated. They have a good balance of natural air infiltration but not so much that they would be considered “drafty”. In these houses ventilation is important but you might also need to add some type of system to bring fresh air in. Calculating how much as we have mentioned above gets a little tricky. Using our 1,000 square foot home example we calculated that you need 45 CFM but if you have a natural air infiltration of 10 CFM now you only need 35 CFM. To determine these numbers you will need to consult an HVAC professional. They are able to run tests on your home to see what your true infiltration rate is.

The Tight Home. These are typically homes that have been built in the past 10 or so years to the higher building standards. They are called tight homes because there is little to no natural air infiltration. This is great for the heating and cooling cost, but not so good for indoor air quality and air exchanges. The good news is that building codes include provisions for a mechanical solution to exchange the air – venting the stale air out and brining fresh air in. There are a number of solutions that are able to do this without a noticeable impact on the HVAC system. It wouldn’t make sense to build a home to gain all the advantages of a tight home, then turn around and lose all of that because you need to bring fresh air in. One of the best systems on the market is either an Energy Recovery Ventilator (ERV) or a Heat Recovery Ventilator (HRV). Both “recover” the lost energy by tempering the air coming into the home.

To learn more about air exchanges and indoor air quality visit https://www.ashrae.org/

For information about exhaust fan options as well as ERV and HRV units, visit www.airkinglimited.com

The Air Balancing Act

When you hear Air Balancing you might have pictures of a puff of air trying to stay on a narrow bar without falling off. While that might be something you would see in the comic section, when it comes to your home, Air Balancing is a bit different and more important. The simple explanation is that the amount of air coming into the home needs to match the amount of air going out of the home.

So what air is going out of your home? There is more air leaving your home than you probably realize. Items such as your furnace, water heater, clothes dryer, range hood, and bathroom exhaust fans can all be pulling air out of your home. All of these items provide a pivotal role in the overall comfort and/or indoor air quality of your home so not using them is not an option.

This is where the balancing comes in. As we defined earlier, balancing is making sure the amount of air going out matches the amount coming in. So where do we get the air (referred to as make-up air) to balance everything? This all depends on the construction of you home. Many older homes have what is called natural air infiltration. The rest of the world knows these as drafts. In newer homes, the amount of drafts has been greatly reduced. You might hear the term – tight home. While this helps with the comfort and efficiency of the home it creates an issue with the air balance of the home and it is harder to account for all the air leaving the home. An easy way to balance the air is to leave a door or window open. That works great unless you live in a climate that has temperature changes (like almost all of the United States). There might be a few weeks of the year that this would be a viable option but in the middle of summer in Arizona or the middle of winter in Minnesota, not sure you want to have a window open. This is where mechanical solutions come in. A mechanical solution like the Air King QFAM is set up to bring fresh, filtered air into the home – balancing the amount of air leaving the home. There are air test that can be done to your home to determine how much air is leaving, then the QFAM can be set to deliver the proper amount of air flow to make-up that air providing a safe living environment.

Wait, you used the phrase “safe living environment” does that mean mine is not? Maybe. If a home is too tight and the air leaving is not replaced, you can create a negative pressure inside your home. Air will always find a way to balance itself and can start pulling from things like furnace vents or chimneys. The negative pressure won’t allow them to vent properly and the harmful fumes, gases and contaminates that should be going out of the home could be coming back into the living environment. For these reasons the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE), who is a leader in writing codes for indoor air quality standards has included a provision for fresh air (or make-up) air in the latest version of ASHRAE 62.2.

Balancing your home’s air is an important element to your indoor air quality and healthy living. For more simple and effective was to accomplish balanced air, visit the Air King website at www.airkinglimited.com.