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Learning, Sharing, and Teaching => Do it Yourself Discussion! => Topic started by: secondcor521 on May 17, 2023, 10:29:56 AM
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Hi all.
I'm thinking of installing an attic fan like this one:
https://www.lowes.com/pd/Master-Flow-Electric-Gable-1600-CFM-Silver-Galvanized-Steel-Electric-Power-Roof-Vent/1002986804
I feel like I can handle most of the job, but have some questions:
1. Will installing this help reduce my overall electric bill? I've got a standard one story house with attached two car garage and a bonus room. 2x4 framing, R-60 in the attic, in Boise.
2. Will installing this help keep the bonus room over the garage cooler?
3. I'd like to put it on the master bedroom circuit, because I really don't have much going on on that circuit. Would this probably be OK?
4. Biggest question - I understand how to attach the Romex to the fan. The other end needs to be connected to the existing circuit. Super dumb question: How do I do that? I'm guessing there are no "spare ends" just lying around. Maybe daisy chain off the light fixture/ceiling fan?
I'm picking the master bedroom circuit because it's close to the electrical panel and the location of the fan.
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You would be much better off with a whole house fan. I highly recommend Quiet Cool. You just need to make sure you have adequate ventilation for it. The other types are really not helpful and use more energy than they help conserve. IMO As for the wiring, you are correct in that you will at least need to make some pigtails to tie into the existing circuit. You find the feed side in the junction box and then tie together the leads that go to the devices. It really depends on what you are tapping into and where it gets it's power from.
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I installed one in my garage with an open ceiling. I like it for that use. I doubt it would make a huge difference to energy bills if you already have R-60 in the attic. You might look at doing air sealing around light fixtures and other ceiling penetrations. That's usually a low-cost/smallish value thing that can help.
I do recommend a QuietCool Whole House Fan as well. Those will help cool your entire home and do make a difference on the energy bill. Your climate might be a bit different, but in Denver I didn't even have to turn on my AC until the end of June last year. And it cut my AC usage by maybe a 20-30% in July and August.
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1) The cheaper way to reduce summertime attic heat is to add more passive ventilation. Ridge vents and "whirlybirds" are easier to install, as they require no electrical connections. Also, take a look at your intake ventilation - which is usually in the soffits. Many houses are built with insufficient air flow here, or insulation has blown over the tops of the vents and obstructed them. I would definitely add more cheap and easy passive vents before getting a powered roof vent. I'd also probably pay a little extra for a solar-powered roof vent rather than wiring one to the house. Finally, if you are within a few years of getting a new roof, maybe try a light-color material at no extra cost and see how much that alone reduces attic temps. It's a dramatic difference.
2) Possibly, but only if you have insufficient ventilation as described above, or excessive attic heat (greater than maybe 120F on the hottest day of the year).
3) You may need to have an electrician assess how many plugs or lights are on that bedroom circuit. The maximum load of all appliances that could possibly be run at the same time is only 80% of the breaker's load (probably 20A x 0.8 = 16A). Each outlet and your light fixture counts toward that load and usually 6-8 plugs or lights max it out. There's a decent chance you cannot add to that circuit, because the cheapest way to wire a house is to max out every single breaker. That said, home inspectors rarely do this time-consuming testing so you would probably get away with it. The downside would be if you had breakers flip when running a bunch of things plus that fan at the same time.
4) There's probably a service box somewhere in the attic you could tie into. The ceiling light box will probably only have electricity when the light switch is on. It would take trial and error to figure out which breaker supplies which box. Some houses (like mine) have everything except the overhead lights wired from the crawl space, so finding a good place to tie in might be challenging.
ETA: Regarding whole-house or attic fans, these only work when you want to exchange inside air for outside air. I.e. the outside air is cooler and there's not too much dust or pollen. First, how often does this scenario really happen? Second, simply opening windows and/or doors will accomplish the same thing, just more slowly. Also I'm wary of any solution that adds penetrations through the insulated envelope of the house, because those penetrations dearly will cost you in the wintertime.
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Thanks everyone.
Some clarifications and additional info:
My main goal is to make the west-facing bonus room with a west-facing window more comfortable. Right now it's about a 5-8 degree temperature differential, making it difficult for my son (bonus room) and me (main floor) to be comfortable at the same time. Secondary goal is to reduce electricity costs.
My house has a standard-for-the-area gas forced air furnace and HVAC system. Single zone. The bonus room has four floor vents and one maybe 12x12 air return in the ceiling.
Exhaust: My house has three gable vents on the north, south, and west sides of the roof. It also has nine box vents about a foot below the ridge. My main roof ridge is about 60 feet long and the garage roof ridge is about 25 feet long. This exhaust capacity probably meets minimum requirements, but more could be useful.
Intake: My house has eleven 5x12 soffit vents which are unonbstructed by insulation because I confirmed this when I DIY'ed the additional attic insulation a few years ago. I believe this meets the basic house building standards, but more could be useful.
I already checked air sealing around lights etc. when I upgraded the insulation and it all seemed to be good.
The insulation is mostly blown in fiberglass on the main floor ceiling. The bonus room is mostly wrapped in batt insulation. There might be gaps; maybe I should double check.
I took a look at the whole house fans and I don't think that's what I want or need for my goals. We already do open the main floor windows and bonus room window in the mornings and evenings, which creates a nice and fairly effective chimney effect.
On a 75 degree day the attic air space is, I would guess, 110 to 120. I start sweating up there within a minute or two. (I was up there in the process of replacing the master bath ceiling exhaust fan.)
I'll consider a lighter color roof shingle (currently it's gray) plus a ridge vent; my roof is due to be replaced in the next few years.
The master bedroom is a 15A circuit, and the total wattage of everything in that room as I use it is about 116 watts plus a smoke detector which I didn't check but has to be minimal. There is a ceiling fan there but I never use it. I guess it mostly doesn't matter though if I don't go the powered attic fan route.
I don't know of any service boxes in the attic. The way they usually build my grade of house around here is to just run the romex up from the service panel, through the attic above the bottom part of the roof trusses in straight lines to the various destinations.
As far as temperature goes, it is, as mentioned, about 110-120 in the attic now with daytime exterior temps about 75 or 80 and with the conditioned airspace of the house at 70 or so. The main problem seems to be in the afternoon as the sun has had a chance to heat up the attic. My thought was placing the attic fan on the north gable vent would create a cross current, sucking outside 75-80 degree air in and pulling 110-120 degree air out.
Additional thoughts welcome.
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To some extent, any house with a second story is going to be 5-10F hotter upstairs than downstairs no matter how insulated it is. That’s just the difference 8-9 feet of elevation makes in an enclosed box. The only way to counteract the natural settling of the air is to keep it in motion.
Consider if you can set up your HVAC with dual intakes so that you can flip a valve to switch which pipe the air flows through each season. In the summer, make it primarily pull from near the ceiling of the upstairs room where the hottest air settles. In the winter, switch it to primarily suck air from near the floor of the 1st floor, where the coldest air settles. This will improve the efficiency of your heating and cooling while moving the air that is most uncomfortable in each season.
That said, if you have a 35F difference between the attic and outside, I think you have a lack of ventilation. Add three soffit vents and a one whirlybird to see if you can get that difference down to about 20F. I did exactly this on a 2650sf house and measured a 15-20F reduction in the attic, which was reaching 130-140F on 100F days. Apparently code minimum ventilation is not enough!
Another option is to attach radiant barrier material to the underside of your rafters. I prefer to add passive ventilation though so the roofing stays cooler and so I don’t hide any leaks.
Another option might be a technique I saw in an ad where a light colored coating is sprayed on the shingles. I have no experience but in theory this would help.
Last idea: install solar panels. These sit a few inches above the roof and essentially put part of the roof in the shade. I can confirm this works as I had this done on my shop. Now it tends to stay cooler than the outside air in the summer even without AC.
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I've had similar problems with my kids southwest facing room getting insanely hot and hard to cool. I have R40 in my attic.
I've tried window inserts without much luck.
We have those cellular window shades in the room, and they don't make a meaningful difference.
I'm skeptical that adding an attic fan would make a huge difference with that much insulation, but I could be wrong. I doubt there's that much heat gain from the attic with R60 insulation. Look at the Quietcool options if you go this route. I installed their solar attic fan in my garage, and am happy with it. It's a pretty powerful fan, and it only draws 40W (when the sun isn't shining), so I'm not worried about putting it on an existing circuit.
Other things I've considered, but never tried:
-Zoning the HVAC: I was quoted $3k for this
-Smart vents: Using Flair Smart vents to mimic zoning. This would have been over a thousand dollars, but might have worked and provided other benefits to the rest of the house.
Things that DID work:
-The Whole House Fan completely fixes the problem while we still get cool evenings and mornings. I can drop the temp in that room (or the whole house) by 7-8 degrees as long as we have temps below about 50. That's enough to pre-cool the room in the mornings and keep the temp differential to be okayish into the evening. It does almost nothing in July and August though.
-We eventually added a mini-split in the room when we installed a ducted heat-pump in the house. This would have been too expensive on it's own, but it only added about $1.5k ($750 if we had opted for a wall head instead of a ceiling cassette) to the cost since it was supported by all of the other components I was already installing. We only need to run it on the hottest or coldest days, but it completely solves the problem when it is run.
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I don't know how much cooler it would make the room below, I think it would be minimal. 5-8 degrees? Maybe. The only way to know is to try.
As far as electric hookup, as was said you need to find a ceiling box that is hot (and that runs two wires back to the switch), not one that is hot at the switch because then the fan would be controlled by the switch with the light. I hope that makes sense.
If you really don't want the ceiling fan you could take it down and control the gable fan from the switch in your bedroom; that would confuse someone in the future, but so be it.
As far as ridge vents, they are the standard now but mainly for aesthetic and installation reasons, the old style vents work fine.
But when you re roof go with the ridge vents.