[stevehull]

AC,

Using CO2 as a trigger for an HRV (or ERV) will not work as a reliable index of home air "staleness". Here is why . . .

The average adult at rest gives off about 200 ml of pure CO2 per minute. Let's think of an really airtight house with four people in it after 7 days.

Assume a house of 1200 ft2 and a height of 8 ft (volume of 9600 ft3 or 270 meters3).

Four people at the end of one week give off 8,600 L of pure CO2 (8.1 meter3).

The increase in CO2 at the end of one week in a literally airtight house with four people is 0.03% (8.1/270)- an almost vanishing small number to trigger with.

A FAR better option is to place the HRV (or ERV) air intakes in the bathrooms running at about 10-20 CFM. When either the bathroom light or shower light goes on, then the blower speed goes up 2-3 times (with a "hang" timer to keep the higher fan on for 5-10 minutes post use).

I used this exact scheme in a home I built over 20 years ago and had indoor winter humidities between 30-35% and summer between 45-50% (no higher). No steam covered windows in bathrooms, always fresh in the home and no mildew in walls.

I looked at CO2, did the calculations and am wondering why commercial units use it. People "believe" CO2 will build up, but in even a super tight home (one air change per day), the use of CO2 as a trigger doesn't cut it.

Thoughts?

Steve