Timing for Mechanical Fresh-Air Intake
I’m in Texas. We have a tightly sealed foam insulated home with a 90% efficient forced air system. From what I am gathering fresh air was brought in each time the system turned on until about 4 years ago. It is now mechanical with high low lock outs for humidity and temperature.
I team into the great debate, some professionals advising to turn it off, others saying 6, 10, 15, 20 minutes per hour with no lock outs, others advising lock outs.
What would be advised? I run higher humidity levels in the attic and primarily hope to get the best setting to keep the attic below 60% as I have been told warm moist air goes into the attic. I know the importance of controlled air intake and to avoid the air through cracks of the home. Hoping to find that sweet spot.
aprilaire recommends 55 minutes for a 60 cfm intake but I see my humidity skyrocking unless I restrict the intake when the indoor humidity exceeds 50% and this may restrict all outside air.
currently I do not have a supply or return in the attic, but interestingly I do notice the humidity increase in the attic when the system turns on vs between runs.
This truly is an art to adjust especially with a foam insulated home, I look forward to your replies.
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Replies
Sue,
I think you need to run it enough to provide sufficient ventilation for the occupants. Articles like this (https://www.greenbuildingadvisor.com/article/how-much-fresh-air-does-your-home-need) give some guidance. Maybe this reply will prompt additional responses from the GBA community.
+1 for bringing it outside air as needed for occupant comfort. The primary need for makeup air is to bring in fresh air for breathing. I think some have used indoor CO2 measurements to optimize the amount of outside air that is brought in for this purpose.
If you have a conditioned attic, fully inside the building envelope, then some registers up there will help to circulate the air and keep attic conditions close to conditions in the occupied areas of the home. You can also set some thermostats to run the blower alone periodically to circulate air, which can help to even out temperature and humidity differences between different areas of the home — especially during any times when the heating or cooling systems aren’t running heat or cool cycles.
Bill