Make-up air and auto-venting in a small air-tight house
I’m building my first house. It’s got a footprint of 475 sq ft with 533 sq ft of living space when the sleeping loft is counted. I am making efforts to make it as efficient and durable as possible given my budget and and making it as air tight as possible is a major component of that effort. For ventilation, I am planning on using the Lunos E2 system which is basically a pair of fans in which each fan blows in the opposite direction as the other for 70 seconds, all the while pre-heating or pre-cooling the inner core component (depending on the temp difference between the interior air and exterior air), then the fans change direction to pre-heat or pre-cool the air being exchanged to minimize heat energy loss or gained (depending on whether it’s heating or cooling season).
My two questions are:
1) I despite the fact that I am trying to achieve an airtight envelope can I get away without dedicated makeup air if I keep my range hood below 400 cfm?
2) I am wanting to vent all my plumbing fixtures (i.e. kitchen, bath, laundry) with auto vents to minimize heat loss through the roof (unvented cathedral with closed cell against the sheathing & the rest with dense-pack) and to minimize the chance of roof leaks. If I succeed in achieving an airtight envelope will my auto vents not work well?
Note: there are no gas appliances, all electric.
Many thanks!
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Replies
Michael,
In a tight house that size the range-hood will need makeup air. How that's supplied is up t0 you. Opening a window is a perfectly viable option.
Your AAVs wouldn't be affected by how well your house is air-sealed. They operate on a pressure that is much higher than the differentials you will create in your house.
Hi Michael.
I suggest you read this. It should help answer your questions: All About Makeup Air
You can use a simple barometric damper for the range hood, this would automatically open when the house gets depressurized.
For a house, you should always have one positive pressure vent, you can use AAV for everything else. Sealing a stack for both air and water is very standard, it would be the least of my worries on a build. You can also bring the stack out through the top of the side wall and run it past the eaves above the roof.