How Much Fresh Air Does Your Home Need?

Brooklyn brownstones are being built with tighter and tighter envelopes, which means there are no leaky cracks to help ventilate the building.

This is a problem, sort of. Gone is the wasted heat. But you need to make up for that air and the best way is good design and mechanical ventilation.

ASHRAE is the group that keeps track of how much a house needs in terms of heating, cooling and general ventilation. Their standard 62.2 is the benchmark of acceptable indoor air quality in low rise buildings.

They suggest the following to find how much air circulation your house needs. It is calculated in cubic feet per minute (cfm) of air change.

Multiply square footage of the house by 0.01
Then multiply number of bedrooms plus 1 by 7.5 (7.5cfm is what one person needs)
Add these together.

For example for the Brooklyn Green Show House we have two unites with a total of 3000 square feet and 7 bedrooms. That would look like this:

(square footage x 0.01) + (bedrooms plus one x 7.5) = cfm
(3000 x 0.01) + (8 x 7.5) = cfm
30 + 60 = 90

This brooklyn green building (i.e. very tight envelope) needs mechanical ventilation of 90 cubic feet per minute to keep the air fresh. That is 5400 cfm per hour, which is almost two total air changes per hour.

That might sound like a lot but a leaky house can do a lot more than that. The good thing about doing it mechanically is that you can use an energy recovery ventilator and recover the heat or cold that is passing out of the house. This reduces energy costs that would be wasted on a leaky house.

About the author: Gennaro Brooks-Church

2 comments to “How Much Fresh Air Does Your Home Need?”

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  1. Gennaro Brooks-Church - August 19, 2009 at 10:52 pm

    Geothermal is legal in Brooklyn. It is also legal in NYC but because NYC is a huge rock (thus the ability to build skyscrapers) it is not practical. Too much stone to dig through. Brooklyn is a little better. But it is very impractical, logistically and financially, having a drill truck working on your front stoop. I’m not sure it is the best use of money. I’ve looked into running the looks horizontally in the back yard but that doesn’t work very well either.

  2. Heather Y - August 19, 2009 at 5:32 pm

    This German technology (PASSIVE HAUS)
    reminds me of what they say about how the heavily advertised “Wave ventilation system” works – only better.

    The Wave expells stale air through a dryer vent like thing in your basement if you have a house. There is another model for apartments,

    The main advertising hook is getting rid of humidity.

    I have to admit that really speaks to me- I can tolerate heat much better if it is not 60 + humid the way it has been this past week!! They also claim to vent out radon, Co2, other toxics that can build up.

    Passive Haus seems better mainly because it is getting that temp erature of about 41 degrees from the earth. Sweet.

    My question is the same one for geothermal- is it possible, let alone legal, to dig deep enough to make this possible in a place like NYC, with all its’underground infrastrcture?

    Especially in attatched housing like the show house?

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