In our HVAC design work, we get sent projects where the client sometimes wants the impossible. They’ve read enough to know they want the mechanical systems in conditioned space, so they put a tiny little closet somewhere in the house and tell us that’s where the equipment goes. If you have any say over the amount of space for the mechanical systems, please make it a mechanical room. A little closet simply is not adequate if you want a high-performance home.
The good and the ugly
Let me start off by showing you two ways to design space for the mechanical systems in a house. Exhibit A is the photo above. The architect provided a whole room for the mechanical systems. Look how beautiful it is! Space heating and cooling, water heating, whole-house ventilation, and more are all in there. The room has plenty of space for ductwork and room to move around the equipment. That last point is something greatly appreciated by anyone called in to service the equipment.
Contrast that nice, spacious mechanical room with Exhibit B, the mechanical closet in the photo below. It’s a tiny closet with an air handler, the return and supply plenums, and the ductwork necessary to get the system connected to the rest of the house. Because of how tight that little closet is, the installers would have had a difficult time making and sealing duct connections. And if it leaks profusely, the service technicians may have to rip out drywall or pull out the whole unit to fix it.
I know. I know. Every square foot of conditioned floor area is expensive and no one likes to give it up. That’s why we end up with tiny mechanical closets like the one above. So if you just don’t want to give up space in the main conditioned area, you have a couple of other alternatives.
The first alternative is to create a conditioned crawl space and put the equipment there. The photo below shows an example of that strategy. The crawl space probably doesn’t get used for anything else, so you’ve plenty of space to make smooth, gradual transitions in your duct system.
The second alternative is to create a conditioned attic. The photo below shows one of the Mitsubishi ducted mini-split air handlers in my conditioned attic. When you do big pair-of-pants tees like you see there, you need space. And like the crawl space, the attic probably doesn’t get used for much else, except maybe storage.
Finding space for the mechanical systems in a house is usually given short shrift. In warm climates, designers often assume they’ll go in the attic or crawl space. Those locations are typically unconditioned, nasty, inhospitable places. Do you really want your expensive equipment with the important jobs of keeping you comfortable, healthy, and clean in such a place? Plus, we know that putting heating and cooling equipment in an unconditioned attic is a terrible idea in a cold climate and can add close to 20 percent to your cooling bill in a hot climate.
Next time you find yourself with any influence over the design of where the mechanical systems are going to be located in a house, just remember: Bigger is better! Make it a mechanical room, not just a closet. And of course, keep the mechanical systems in the conditioned space.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and writes the Energy Vanguard Blog. He also has a book on building science coming out in the fall of 2022. You can follow him on Twitter at @EnergyVanguard.
Lead photo of spacious mechanical room from U.S. Department of Energy, Building America Solution Center
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