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Community and Q&A

Supply-only whole house ventilation

markd0 | Posted in Mechanicals on

All the whole house ventilation systems I read about are exhaust only. I am thinking about supply-only ventilation. Is there any reason not to do it this way?

In my microclimate during summer it’s mid 80’s during the day but there’s usually a strong cool breeze by early evening with lots of cooling potential. But the breeze hits a side of my house with no operable windows and because of deep porch eaves, landscaping, fences etc. the breeze tends to sort of roll over the house rather than envelope it. I am thinking to put an intake and fan on the breeze side and duct into the house through ceiling. I can’t find any references to supply-only whole house fans like, this, so wondering if I am missing something.

I do understand that this isn’t venting the attic like the normal whole house fan system, but my roof has spray foam on the underside and the attic isn’t super hot (or at least it’s no where near as hot as it was before foaming).

For context, this is in temperate west coastal climate, is house has no air conditioning and hydronic floor heat, so no existing ductwork. But it’s a very simple layout and attic ductwork for ventilation to ceilings would be very simple. Main house is basically a 20’x60′ open rectangle.

I also need range hood (1000 cfm) make-up air and thinking I can combine the functions.

So I’m basically thinking a straight ~14″ duct down the length of the attic and a variable speed fan with up to ~1000 cfm. I could blast it for fast evening cool-down in summer, turn on anytime with range, and have it at near idle for routine ventilation.

Does this make sense?

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  1. GBA Editor
    Martin Holladay | | #1

    It sounds like you are more interested in nighttime ventilation cooling than in a conventional ventilation system.

    If you want a whole-house ventilation system that is designed to provide fresh air rather than nighttime cooling, you can certainly do that. The most typical system is a central-fan-integrated supply ventilation system; since you don't have a forced-air system, however, your system would be different. If you are designing a supply-only ventilation system that is not tied to a furnace or air handler, the system would typically use a fan rated at 100 cfm or less. For more information, see Designing a Good Ventilation System.

    If the main purpose of the system is nighttime cooling, you would design the system like a whole-house cooling fan. For more information on these systems, see Fans in the Attic.

    Because you have an insulated unvented attic, you would have to include a very large intake grille somewhere in one of your walls, and fairly large ductwork. One system that uses some of the elements you are talking about is the Nightbreeze system. For more information on Nightbreeze, see:

    Cost-effective night purging techniques


  2. markd0 | | #2

    Yes, I am mainly interested in nighttime cooling. I've read Fans in the Attic. Like everything else I've read on whole house fans, it assumes exhausting the house with windows as intake vents. My question is if there is any reason not to reverse this, and force supply air into the house with a fan & ducting, with air exiting the windows.

  3. GBA Editor
    Martin Holladay | | #3

    As I wrote in my first response, there is no reason you can't do this, except for the fact that you need a very large intake grille in one of your walls, and the ductwork will also be large.

  4. markd0 | | #4

    I admit "no reason I can't do it" is less specific than I was hoping for. Is there any reason not to do it? Is it a dumb idea? Why does it appear to be nearly unprecedented? Is it just because whole house exhaust-through-attic fans are cheaper and simpler?

  5. GBA Editor
    Martin Holladay | | #5

    Q. "Is there any reason not to do it?"

    A. Here are some possible reasons:

    1. Some people don't want to see a 36" by 36" intake grille on the side of their house.

    2. Most homes don't have enough room for the required ductwork.

    3. If the homeowner forgets to open the windows before turning on the fan, the entire house will become pressurized, driving indoor air into the walls and ceiling.

    4. Whole-house fans that blow into vented attics are simpler and cheaper to install.

  6. tommay | | #6

    If you have a fan blowing into a house you will pressurize it raising the temperature. Exhausting hot air, should be what you are thinking, lowering house pressure. If you install a fan in the attic, close all other windows during the day except for one or two basement windows, along with basement and attic doors. This will exhaust the hottest air while drawing in air through the basement cooling it.At night, crack open several windows to cool off those rooms. Use CFM's to determine how much to open each window to get an even flow in each room.

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