I air-sealed my attic too well!
Not really, of course. But here’s my story:
I moved into a 1350sf ranch home (3/4 basement and 1/4 crawl) in Columbus, OH last year and have been working to air-seal and insulate it. I ran a blower door test before I began just to be nerdy and track my progress. Initial leakage was 3075cfm @ 50 Pa, about 9.7 ach50. I started work in the attic, sealing up everything I could find before blowing in cellulose over my skimpy loose fiberglass.
Next up: my walls. My 2×4 walls are completely un-insulated, and while researching local contractors to dense-pack I found out that my natural gas utility offers a good rebate program for weatherization work. They required a 3rd-party energy audit to be performed first in order to properly specify cost-efficient work. The audit was discounted to only $50, and refunded in full when any of the specified work is performed. Sign me up!
I had the audit yesterday. The good news: my blower door tested at 1620cfm@50, about 5.1 ach50 (I thought this was great considering I haven’t even touched the walls,basement, rim joist, and a couple of un-weatherstripped doors). The bad news: the rater said this fell below my home’s BAS (Building Airflow Standard) of 2000cfm@50 and that I could not receive any rebates for dense-packing my walls unless I had mechanical ventilation installed. I asked him how much ventilation. He replied, “20-30 cfm”. I asked him about the 85 cfm exhaust fan in my bathroom with an occupancy censor and 10 minute post-delay. He said, “we could maybe consider that, but only if you set it up to run 24/7.” What?! I wanted the rebates, so I said, “wait right here, it will be set up to run 24/7 in just a few minutes.” His reply, “sorry, sir, but we’d have to see documentation that the ventilation system was set up by a licensed HVAC contractor.” Argh!!!
TL:DR: I sealed part of my house before learning about a generous rebate program that I would have qualified for. Now my house is too tight to get rebates unless I hire an HVAC contractor to install a mechanical ventilation system.
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Replies
Ben,
It sounds like you are faced with the prospect of jumping through a bureaucratic hoop.
Perhaps the cost to hire a HERS rater to verify the air flow of your bath exhaust fan will be less than the value of the desired rebates. On the other hand, if it costs more for the ventilation inspection than the rebates are worth, you'll just have to pay for the weatherization work out of your pocket.
Martin,
Yeah, that appears to be the choice. The utility is offering $300 back for dense-packing the walls (I haven't gotten a quote for the work yet, but I'm guessing it would be $1500-$2000 before rebate). Between the cost of a HERS rater (at least $100 just for coming out) and the added hassle I think I'll be better off just leaving the rebate alone. I was particularly annoyed that the rater who came out did not want - or did not know how - to grade my bath fan's suitability for ventilation (he was BPI certified). Oh well....
Regardless of the red tape, I have been curious about whether or not I'll want additional ventilation once I complete my weatherization work. Humidity and IAQ are not even close to a concern right now, despite the blower door results. Once I tighten everything up, however, I may want to install an additional fan (or keep my current fan on 24/7).
Ventilation is a personal choice IMO. I'm not a "fan" fan. Is that fan^2? Can't be. Fans aren't square now are they. Circle up the fans for circular fan discourse.
I put Panasonic fans on with the main light. Enough fan for a somewhat right home. Stuffy day, huge party just leave the bath light/fan combo on.
I like simple. Also a fan of digital timer switches if the humans aren't trainable.
I believe you can find an approximate natural ventialation(leakage) rate based on your current blower door test. Then compare that to the ASHRAE or BSC ventilation recommendation....
My take is that if you are using bathroom fans for extended periods (for farts or for shower humidity) and/or have kitchen exhaust - that you get a decent amount of fresh air already. Not to mention if yo8u are taking the dog out on frequent walks or kids going in/out all the time.
The little timer switches are great to allow for extended 1-4hr exhaust modes etc when outside air conditions are mild.
If very cold stack effect will help most of the time to flushout house. (or moisture on windows will tell you your humidity is too high).
A high efficiency fan upgrade in a bathroom will definitely help with the electric bill if you end up running for a few hours a day. If one is extra old or starting to get funky on ya...might be due.
If they're only giving you a $300 rebate on $1500-2000 worth of work, it's not a super-generous rebate. Go ahead and insulate the walls on your own dime- no matter WHAT you are using for heat, it will have a decent internal rate of return. (Weatherization programs in my state offer 75% off up to a total benefit of $2000 for audit-authorized projects, and that's on an annual basis- do the walls one year, the attic the next, etc.) Dense packing the walls WILL tighten the place up even more, but it's unlikely that just that measure would drop you from 5ACH/50 to 2 ACH/50. You might limbo under 3 ACH/50 though, which would bring you to IRC2012 code-max air leakage, a point at which some amount of active ventilation might be a good idea.
Buy few $10 AcuRite or similar humidity monitors (available at box stores and other places), and put them in a few different rooms (but not the bathroom- which will have periods of extreme humidity.). If the relative humidity is running above 35% @ 70F in most rooms all January/February (the temperature matters- us a psychrometric chart or calculator to normalize it to your actual interior temps) you may need to ventilate more to keep the exterior sheathing happy & mold-free over time.
After dense packing, sealing the band joist and fixing the door weatherstripping, get religion about running kitchen exhaust fans EVERY time you're cooking or baking produces a substantial amount of indoor air pollution that won't just dissipate the way it did when you were pushing 10 ACH/50. Burn the toast in the AM one day you'll still be smelling it the evening of next day unless you actively ventilate (and that's just some of the not-so-great stuff you can sense directly with your nose.)
Dana and others,
Thanks for the input. The work is definitely going to happen, even without rebate (though I wish we had rebates like yours!). I've already got a couple of those humidity monitors bouncing around the house and I'll be sure to keep 'em close as the house gets tighter. You do have me a bit worried now, though, with your recommendation of <35% RH. I generally see a RH of around 40-50% in most rooms, which I thought was ok. Maybe I should really be adding more ventilation after all...
My bath fan, by the way, is a pretty good one. 85 cfm Panasonic whisper-series with a straight run of smooth 4" duct. I'll try running it for longer periods and see how that affects my RH levels.