I was wondering whether there would be issues with piping the exhaust from an HRV into an attached garage (while the fresh air intake still comes from outside).  The garage would have vents installed to allow the air from inside to garage to exit to the outdoors.

It seems that this would provide for some flushing of stale garage air, and possibly a small amount of heat (to the extent that the HRV was not able to extract it from the exhaust air).

Thoughts?

Thanks,

Jeff

It's probably not going to fly with the building code checker!

 

John

Since it is an exhaust it might "fly" with the inspector.
If you can get around to sealing and proving that air can't protrude from the garage to the house it might
work. Bit sceptical though. However I like the idea since the air exhausted is dehumidefied and wouldn't add condensation to the garage. Code does speculate that you simply can not do this but it's worth a try.
Check with the local inspector before hand. I'd hate for you to core a 6or8 inch hole and have to fill it and seal it aftewards.

The air from an HRV won't necessarily be dehumidified. In winter, with inside air at 70 F and 40% RH, the dew point is in the mid to upper 40s. The cooled exhaust from the HRV could at times be at 100% RH, with some condensation having occurred within the HRV. Depending on how well he garage exterior walls are insulated, they could be easily be still colder than the exhaust from the HRV, and adding moisture from the inside of the house wouldn't be a good idea. At other times, mainly milder weather, the garage surfaces could be above the dew point of the inside air and there would be no problem. If it were me, I wouldn't discharge the HRV into the garage, due to the humidity problem potential.

As to "heating" the garage with the HRV exhaust air, the amount of heating would depend on the approach of discharge air to the outside incoming air temperature. Again, depending on how well the garage is insulated and the performance of the HRV, the temperature inside the garage otherwise could be above or below the HRV discharge air. At times you could be heating the garage, and at other times cooling it.

The moisture condensation and the hope of getting some heat into the garage will work against each other. If the garage is sufficiently well insulated, then it is more likely to be warm enough to avoid moisture condensation but it also is less likely to be heated further by the HRV discharge. Similarly, if the garage is not insulated at all and thus closer to the outside air temperature, it will be more likely to cause moisture condensation but also more likely to be warmed a bit by the HRV discharge.

Thanks for the replies...

I'm just east of the Rockies in Colorado, where we struggle to keep the interior humidity at 30% in the winter...  Without running a humidifier, the interior humidity would drop to 20% or lower.

I am in the process of insulating the garage, and eventually heating it with radiant heat from the slab (already insulated to R-10 underneath and around the perimeter).  I plan to keep it at 50-60 in the winter; I suppose the HRV exhaust could easily be colder than that, which would make my idea not so good.

I was trying to think of a good way to provide some air flow in the garage as I think it is unusually tight with 1" of foam in the exterior walls and doors that seem to close very tight as well -- no visible light around the perimeter of the garage doors.  The living space portion of the house is off-the-scale tight, hence the need for an HRV, at least according to the free energy audit from our electric company.  (The auditor recorded 2 air changes per hour WITH the blower door in place, with a "C8" fan configuration and 814 CFM through the fan.  The conditioned portion of the house is about 4000 square feet with an average ceiling height of about 8 feet).

Jeff

Posted By JeffInCO on 16 Jan 2011 04:23 PM
Thanks for the replies...

I'm just east of the Rockies in Colorado, where we struggle to keep the interior humidity at 30% in the winter...  Without running a humidifier, the interior humidity would drop to 20% or lower.

I am in the process of insulating the garage, and eventually heating it with radiant heat from the slab (already insulated to R-10 underneath and around the perimeter).  I plan to keep it at 50-60 in the winter; I suppose the HRV exhaust could easily be colder than that, which would make my idea not so good.

I was trying to think of a good way to provide some air flow in the garage as I think it is unusually tight with 1" of foam in the exterior walls and doors that seem to close very tight as well -- no visible light around the perimeter of the garage doors.  The living space portion of the house is off-the-scale tight, hence the need for an HRV, at least according to the free energy audit from our electric company.  (The auditor recorded 2 air changes per hour WITH the blower door in place, with a "C8" fan configuration and 814 CFM through the fan.  The conditioned portion of the house is about 4000 square feet with an average ceiling height of about 8 feet).

Jeff

The dew point of 30% RH 70F air at 5k' of elevation is 37F- anything in the garage that's at 37F or lower would be at risk of condensation, and even if the garage is 50F the RH in the garage would still approach mold-growth levels with a constant supply of HRV-cooled conditioned space air that started out at 35%RH/68F.

Installing the little Panasonic FV-04VE1 single-room ERV for the garage-only could provide at least some ventilation to a tight garage without introducing moisture, or cross-mixing garage air contaminants into conditioned space air etc.  It maxes out at 40cfm, but can be set lower (10-20cfm) if desired. ( A 25'x25'x10' garage would still get ~2.5ach @ 40cfm.)