Return air through basement
I am unexpectedly going to have a basement. It will be insulated, conditioned and dry, but not habitable per code. I’m also unexpectedly going to have a heat pump instead of mini splits. The air handler will be in the basement. We will have no combustion appliances.
Can I return air with transfer grates to the basement, and use the open space of the basement as the return path to the air handler? Is this a bad idea at all?
I note that the IRC says: “Return air shall not be taken from a closet, bathroom, toilet room, kitchen, garage, mechanical room, boiler room, furnace room or unconditioned attic.” Would I need to construct a little rooms around the air handler and water heater to make this code legal?
–John
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Replies
My home was designed without return ducts. It works because the floor plan is open and any doors that would restrict airflow are louvered. That said, you probably should talk to your code enforcement office to see if they will sign off on your proposal.
John,
I strongly urge you to design and install return-air ducts. What's your reason for resisting the idea?
If you have a basement, installation of a return air system should be relatively easy.
Well, return ducts would be more expensive and have higher static pressure, and I will already have a basement that amounts to an enormous open plenum. I'm not resisting ducts. I'm just wondering what the advantages of ducts would be in this case.
John,
The best type of return air system includes a return from every room where it's likely for a door to be closed. You can override the need for a return in every room by installing jumper ducts or transfer grilles, at some loss of acoustic privacy. Of course, jumper ducts can cost almost as much as return-air ductwork.
Leaving the door open at the top of your basement stairs would be possible but unusual. I suppose you could install a louvered door at the top of your basement stairs if you wanted.
Here's the thing: Houses get sold. Just because you want to leave all of your doors open all of the time, doesn't mean that the next people who buy your house will be happy with that approach.
I'm not proposing having all of the return air go through the basement door. I'm proposing using transfer grates to basement, where the basement then acts as the return plenum to the furnace. Each room would have its own transfer grate to the basement. There would be no need to undercut doors or leave them open. The static pressure for the supply to each room will less than if the returns in the basement were ducted.
This is the airflow path:
Air Handler -> Ducting -> Supply grate in room -> Transfer grate in room -> Open Basement -> Air Handler
John,
The biggest drawback to your suggested solution is the loss of acoustic privacy. When the kids are playing in the basement, they'll hear everything that's going on in mom and dad's bedroom.
If your air handler is noisy -- or your laundry equipment, or water pump, or anything else located in the basement -- everybody in the house will hear the equipment turn on and off.
It's not a habitable basement. It probably won't even have an entry from the interior of the house. Will noise coming from other rooms, going into the basement, and coming back up be worse than noise going through return ducts?
Any other downsides? I guess it depressurizes the basement, which could be a radon concern.
--John
Have you considered the airtightness of your basement? The foundation-mudsill-rim joist-subfloor intersection is often leaky and hard to seal. I would think a return duct pulling from those floor registers in each room would help separate the basement airtightness and radon concerns from your HVAC & living space.