ERV help
Here are the details on our house build:
1792 square feet plus full basement, zone 5. 3 bedroom, 2 bath. 4 people in the house
3” foam on exterior(1.5” seams taped and staggered), osb air sealed with Prosoco seam filler and flashing. 2×6 studs 24” o.c. filled with fiberglass batts. Cathedral ceiling (over living rm/dining rm/kitchen) with combination of 2” of cc foam, 5” of oc foam and fiberglass batts. The remainder of flat ceilings with 16” of blown-in cellulose. The basement walls will be insulated also with rigid foam. The windows are from Alpen with low u-value numbers. The basement windows are not efficient at all, including an egress window so I’m not sure I will need much ventilation down there.
I plan to vent into the great room, and 3 bedrooms and exhaust from the 3 bathrooms, laundry room, and kitchen. I am interested in the Panasonic Intelli balance, but it is recommended for 2,000 sq feet homes. If my calculations are correct, I need 138 CFM as per the ASHRAE 62.2 formula. I tend to lean towards Lstiburek on the lower rates needed but I wonder if this too much of a stretch? I really like that the Intelli balance is adjustable but I don’t want to come up short either on fresh air. Any help is appreciated.
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Replies
Michael,
Here is the ASHRAE 62.2 formula:
7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area.
In your case:
(7.5 x 4) + (3 x 18) = 30 + 54 = 84 cfm.
The Panasonic Intelli-Balance is rated at 100 cfm. So you are all set.
My calculations are incorrect, as always, thank you for your help Martin!
Don't exhaust from laundry and kitchen, you'll get a bunch of lint and grease into the ducts. Fresh air into bedroom could be uncomfortable due to temp difference, also are you sure the outside air won't have periods of say smoke etc in the middle of the night.
Anon3,
I'm not sure where you are getting your information from.
Pulling exhaust air from a laundry room is very common.
Pulling exhaust air from a kitchen is less common, but it is often done by Passivhaus builders. If you pull exhaust air from your kitchen, install the grille in the ceiling or high on a wall, as far as possible from the range, and everything will work fine.
Supplying fresh outdoor air to bedrooms is standard operating procedure. As long as the fresh air register isn't directing the air stream at the head of the bed, you'll be fine.
Why are you worried about "periods of smoke in the middle of the night"? In your neighborhood, does the air get smoky after the sun goes down? If so, why? Perhaps neighborhood hooligans light fires to keep warm, but only at night?
Laundry room is full of lint, it'll turn the ducts nasty over the years. And have fun cleaning your ERV exhaust filter monthly...
The outside air where I'm at is nasty... during initial cold wave people start to burn wood and there's smoke in the air, depends on the wind it can get nasty. Also, I ran into a case where the city contractor runs their wood chopper in the "middle" of the night, and I get gasoline fume into my house, holy shit. They stopped doing it thankfully. If I had fresh air vent into my bedroom I'd be gassed.
So yeah, fresh air vent into bedroom could be a mistake depending on where you are.
Anon3,
The easiest way to reduce the amount of lint in your laundry room is to clean the lint filter on your clothes dryer every time you use the dryer, and to empty the wastebasket regularly. Trust me. These steps will make a difference.
Concerning your second point -- whether introducing outdoor air into a home improves or degrades the indoor air quality -- there is plenty of research on the topic. In almost all cases, introducing outdoor air into a home improves the indoor air quality. There are a few exceptions -- for example, if you home is next to a truck stop where tractor-trailers idle their engines for 24 hours a day. For more information, see All About Indoor Air Quality.
Wow! Luckily, we are in the country with no one real close by...although I did have a neighbor doing a "controlled burn" in his woods early part of the season and the wind was blowing our way. I was more concerned about him burning down my house that was under construction. We do actively clean the lint filter, so it shouldn't be a problem. Sometimes we will do a partial hang dry of our clothes so I'm hoping some of that moisture will be removed with ventilation.
Whether you use mechanical ventilation or not, you are bringing outside air in. I'd rather it go through the hrv filter than through the walls and floors.
I don't know about other hrvs, but our Zehnder filters can be changed in about thirty seconds.
For people who did live in places where outdoor air quality is a problem, a well designed HRV or ERV system can provide good filtering. In particular, if an activated carbon filter is called for, placing it after the heat exchanger on the incoming air, so it's filtering semi-conditioned air can make it more effective. (You also need a filter before the heat exchanger to stop dust that might otherwise clog the heat exchanger.)
Since we're talking incoming air filtration, has anyone done their own fresh air filtration system? Something that would use common furnace filters? A stack of three 20" x 25" filters (coarse to fine) would filter much more effectively than the small filters included with most HRVs, with less pressure drop and would likely be cheaper than buying the HRV-specific filters.
I just caught something in calculating the cfm required for the erv...does the basement not count towards the final number? Our total conditioned space is 3,600 square feet.
Martin's calc (7.5 x 4) + (3 x 18) = 30 + 54 = 84 cfm
Mine (7.5x4) + (3x36)=30 + 108= 138 cfm
Sometimes I wonder if the basement really needs ventilation though(with the cheaper windows).
Michael,
Whether or not to include the basement in your ventilation calculation depends on whether it is finished.
If it has a concrete floor, a furnace, and a water heater -- don't include it.
If it has carpeting, drywall, and two bedrooms -- include it.
Ok, thanks Martin