Install HRV in existing home with dedicated ductwork
I am a new homeowner and just getting my feet wet with all of this stuff but I find it very interesting. I have purchased a relatively new home (2001), two story, about 2400 sq ft. with a partially exposed basement. I am planning on finishing the basement and the first thing I would like to do is spray foam the rim joist area as well as the above ground portion of it. This decision started me thinking about getting some sort of ventilation system in the house before I seal it up. A friend suggested adding a fresh air intake to the furnace but from my limited research it seems that an HRV with a dedicated duct would be the cadillac solution. I would like to go for that unless it is too cost prohibitive. Some questions I have are:
1) I have two baths on the upper floor (vent thru attic and out), a powder room on the main floor and plan on adding a bathroom in the basement. Would it be feasible to tie all these exhaust lines into one and run through the HRV or just leave them “as is” and add supply exhaust lines elsewhere in the house that are easier to run?
2) Would there be a preferable place to locate the HRV…attic or basement? Either way it seems that running installing ductwork would be a major pain if I wanted it to touch all three levels.
3) If I want to get fresh air to all three levels would it be worth considering one HRV in the attic and one in the basement? This could simplify ductwork but obviously increase material costs.
4) How do you “balance” the ventilation with an HRV if you have range hoods, dryer exhaust, and bathroom exhaust fans that are not tied into the HRV? Once the system is in balance doesn’t it just get thrown out of whack when you switch on the range hood? Or is the effect negligible since it is on for a limited time an the HRV is on all the time?
5) Has anyone used “mini ducts” (made by Unico for example) to simplify installation?
6) How about installing the HRV in the basement and have it supply and exhaust only to the main living area to simplify things?
Thanks for taking the time to read my questions….I realize some may be stupid questions but as I mentioned I am just getting started. I appreciate any and all responses.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Tim,
1. If you are going to the trouble of installing spray foam in your rim joist area as well as the above-ground portion of your basement walls, then you should spend a little more money and install the spray foam all the way down to the footing. In other words, insulate your basement wall. Get it done right and get it over with.
2. If you want to install a Cadillac ventilation system — an HRV with dedicated ductwork — then the HRV will be pulling exhaust air from all 4 bathrooms. You will no longer need bath exhaust fans or bath exhaust ducts, because the air from your bathrooms will be exhausted through the HRV.
3. The HRV must be in an accessible location so you can service and change the filters on a regular basis. That means it's much better to install an HRV in the basement than the attic. And if you can't find an accessible location, or if you have no intention of servicing the filters, don't even bother to install an HRV.
4. "If I want to get fresh air to all three levels would it be worth considering one HRV in the attic and one in the basement?" No.
5. "How do you 'balance' the ventilation with an HRV if you have range hoods, dryer exhaust, and bathroom exhaust fans that are not tied into the HRV?" We'll take these one at a time. Your house won't have any bathroom exhaust fans that are not tied into the HRV. Your house should have the smallest possible range hood fan — 200 cfm or less — and you should use it rarely; when you need to use it, crack open a window. That leaves the clothes dryer. Most clothes dryer fans are in the 100-200 cfm range. Your clothes dryer will indeed unbalance your system, but the depressurization is too small to cause problems.
6. Ventilation ducts are usually either 4 in. ducts or 6 in. ducts. You don't want to go smaller than 4 in. Duct seams must be meticulously sealed.
7. "How about installing the HRV in the basement and have it supply and exhaust only to the main living area to simplify things?" Well, you can do that. Remember, though, it's a shame to spend $2,000 for a ventilation system and not hook it up the way it is intended. But if you do that, you'll still be improving your home's air quality. You just won't be getting much fresh air in your bedrooms.
Tim,
Martin has covered this well, my question is, do you need additional ventilation? Have yor house tested by a skilled energy rater and find out the ach50 ( air changes per hour @ 50 Pascals) is for the house. Anything much over 3.5 ach50 for your house and the natural air change (nac) will about cover the continuous ventilation requirement. Sealing the rim joist will tighten up the house some but will not turn a leaky house into an airtight one.
Thanks, Martin. I did get the same recommendation from the spray foam contractor to go ahead and get the whole basement done since it is a fixed cost for the truck to come out. Of course I would expect the contractor to recommend that....I will take closer look at the costs of rigid foam vs. spray foam and may indeed opt for getting everything done in one go. I have a HVAC contractor coming out to estimate costs for an HRV. Thanks for the education.
Doug - I do plan on getting an energy audit done before I go too much farther so I will specifically keep an eye on the ACH figure. Having said that...I would enjoy the peace of mind knowing that my air changes are controlled and not coming from the garage area. We'll see what happens....thanks again.