I have read that one of the reasons sips insulate better than typical stick construction with fiberglass bats is because of the tight envelope. So tight that an air exchanger is necessary. Yet an air exchanger is another up front expense and also another energy consumer -- even as a heat exchanger. As the name implies, heat is being exchanged therefore heat is being lost or gained. So my question is: where is the breaking point where a fresh air exchanger is required and why go beyond it. There must be a point where you can stop sealing up every little crack so the house can still be very well insulated and pretty tight but avoid the upfront and ongoing expense of a fresh air exchanger. I ask this because we go many months out of the year with our windows open or maybe open at night and closed in the daytime during spring and the opposite in the fall. Any ideas or comments? Thanks, Brett

Brett;

I have only installed an ERV in 2% of the SIPs homes we have built, mostly at the request of the owners. I no longer recommend them. We install a dampered 4" fresh air supply to the cold air return. It provides fresh air with no additional electrical cost. Initial cost to install is $50.

Although I have an ERV in my own home I rarely use it and will not install one in my next build. ERVs are over-rated, no matter how tight the home is there is still leakage and you still open the door to get in and out.

Maybe it depends where you are. In Philadelphia it seems like the windows are closed at least 6 moths out of the year because it's either too cold or the night time temps go down to 70 for just an hour or two in the summer. Or in the summer the kids are out late going to bars and screaming at their boyfriend or girlfriend.

So if the windows are closed a lot an ERV makes a big difference. You can really tell when fresh air is coming in. The electrical costs to run it are the equivalent of a 100 watt incandesant and factoring the heat exchange lowers even that cost. Plus you get fresh air!

That's my theory but I have no proof. Someone must have proof.

Posted By palmtree on 02 Jun 2010 11:59 PM
I have read that one of the reasons sips insulate better than typical stick construction with fiberglass bats is because of the tight envelope. So tight that an air exchanger is necessary. Yet an air exchanger is another up front expense and also another energy consumer -- even as a heat exchanger. As the name implies, heat is being exchanged therefore heat is being lost or gained. So my question is: where is the breaking point where a fresh air exchanger is required and why go beyond it. There must be a point where you can stop sealing up every little crack so the house can still be very well insulated and pretty tight but avoid the upfront and ongoing expense of a fresh air exchanger. I ask this because we go many months out of the year with our windows open or maybe open at night and closed in the daytime during spring and the opposite in the fall. Any ideas or comments? Thanks, Brett

we put one in our house.  we actually haven't moved in yet (3 weeks!!!!!) so I don't have any real world experience, but I can tell you my thought process.  we're going to be in the house a long time.  air quality is probably the #1 concern.  If your house is full of stale air, I don't know that you realize it, because it's gradual - but I think it does take its toll on your health.  As mentioned before, I think where you live is a factor too.  I live in WI, so we have the windows closed & possibly furnace on from october through march, for sure, and then probably have a solid month of windows closed & ac on - that's 7 months of the year.  So there's your health, and also the health of the house.  Not that it's automatically going to happen, but I think you run more of a risk of moisture & mold building up in the home if you don't have good ventilation.  I think the total cost of ours was about $2000.  Not insignificant, but if you look at it in terms of a mortgage payment, it's probably an extra $10/month.

jerkylips,

WI and extreme cold climates are more in need of an air exchanger due moisture build up in winter, $2K is a little pricey

There are two types of energy-recovery systems: heat-recovery ventilators (HRV) and energy-recovery (or enthalpy-recovery) ventilators (ERV). Both types include a heat exchanger core, one or more fans to push air through the machine, and some controls. The main difference between a heat-recovery and an energy-recovery ventilator is the way the heat exchanger core works. With an energy-recovery ventilator, the heat exchanger transfers a certain amount of water vapor along with heat energy, while a heat-recovery ventilator only transfers heat. The part of the country in which you live will dictate that type of unit that is right for your needs. Generally speaking – HRVs are usually recommended for colder climates with longer heating seasons. ERVs are used for warmer, more humid climates with long cooling seasons.