1 Power Ventilator
1 HVAC air handler in the attic
1 HVAC air handler in the basement
Temperature today: about 80 or so
Roofing shingles color: Light grey not black
Power Ventilator Question:
Today I had to go up in the attic. Arrrgggghhhhh too old to climb around in a cape cod attic.
Anyway, I noticed it was very cool up in the attic. Which makes me wonder should I even have the power ventilator turned on? Do you suppose it is drawing the cool air from the living quarters up stairs? Or is this a good sign? The attic is very well if not over insulated with batts then blown in rock wool or whatever the heck that itchy stuff is.
Upstairs living area:
My kids tell me they are quite comfortable even on the hottest of days, up there. I would not know since their rooms are banned under the nuclear arms and fallout and parents agreement. AT least that is what they look like to me.
Good question. The kid's rooms being comfortable has little to do with the power vent question. Comfort is a factor of how well the upstairs A/C is performing and how well the upstairs rooms are airsealed to keep out attic air and insulated against radiant heat transfer from the attic. If the HVAC contractor did a proper Manual J then you can expect a comfortable upstairs regardless.
As for the powervent pulling conditioned air into attic, you need to look to make sure your soffit vents are clear and not covered with insulation or painted over to the point of being useless. A simple test you can do as a HO is to take a stick of incense and turn the power vent on and then from inside the house smoke around any ceiling or attic penetration and see if the smoke is being pulled through the openning. You'll need to let the power vent run for a while to set up a draw.
Attic temperature is dictated more by shade than outdoor air temp. If it's 80 and cloudy an attic will be cooler than if it's 80 and sunny.
Attic temperature can be affected by ductwork that leaks very badly. Check the connections to make sure you can't feel cold air blowing in the attic. If you have that get it sealed up with Mastic, aka duct butter.
It could be pulling air from the house. I'd suspect three causes and after observing for a few warm days, you might be able to make sense of which one really is the cause.
The possible causes:
1)EVERYTHING'S OK, nothing to worry about. Probably a cloudy day, only got hot briefly, insulations doing a good job, Fan's doing its job well.
2) FAN IS PULLING AIR FROM HOUSE - Already discussed above.
3) LEAKY A/C DUCTWORK IN HOUSE - Check ductwork joints and air handler for any air escaping. This would greatly effect how hard your AC has to work.
Good luck solving the mistery. Let us know how it turns out, rarely do we hear the ending. Most of us can still learn something too.
naysayer, skeptic, conspiracy theorist
at what temp does attic fan turn on?
are you drawing in humid air?
read at BUILDINGSCIENCE.com
what is your a/c cost per DegreeDay per sq ft?
are all of your elec boxes sealed to the wall?
are your supply register boxes sealed to the ceiling ( floor )?
are your pipes & air handler insulated?
Attic ventilator fan
Hate to be such a naysayer but around Houston where I live, many people who sound like bonafide experts, say not to use a power fan to ventilate an attic. They say it uses more watts than it saves, and that getting to good PASSIVE ventilation standards gives you as good performance. I kinda believe them after making a couple years very sincere study of house energy issues. My fat notebook of energy ideas contains nothing positive on these devices.
The fact that hardware stores sell you these things, does not impress me at all that they deliver results. Guys will sell you and me all sorts of placebos, at whatever price the market will bear.
I think Building Science Corporation, or Florida Solar Energy Center, or any other credible knowledge center will support my skepticism on attic ventilation fans.
I used to work in a utility, in the department which studied load in houses and businesses. Believe that was a fertile place to learn about what works. Definitely it convinced me to be 99% skeptical about claims of savings, most people are FAR from understanding the math background necessary to prove anything. Our department did work at proving what we could, and believe me that required some advanced knowledge of statistics. I'm not bragging because I am marginal at that math myself, but it helped me understand what to look for when searching for *credible* proof of results.
Hope this helps -- P.Student
P.S. The questions posed by CEM-BSEE will probably sound awkward to you, I would not expect you to be able to answer all of them. But if you could, you would be well on the way to studying your situation like the educated experts would.
You said it was 80 degrees when you went up into the attic. You missed the most important question, though- was the sun out?
The question of whether or not to use an attic ventilator fan is widely debated. I can say from experience, though, that if your attic venting was set up originally to use an attic ventilator (normal soffit vents around the eaves, but few or no vents at the top of the attic except for the power vent) you'd better keep using it unless you have more vents put in up top.
Passive ventilation only works if the attic is set up for it, and that's not always the case. My house had a power vent put in when it was built, so they put NO other vents up top. If it is turned off (or the motor dies), attic temperatures go nuclear, and my normally slightly oversized AC can't even keep up. Last time the vent motor burned out, I knew something was wrong immediately, and for just that reason.