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whole house VS attic fan or both?

johnm07's picture

I am in the middle of a major remodel on a 1920s home in Northern California and need some advice on cooling. We are installing radiant floor heating and a gas stove for heat so this leaves us without an HVAC system. Our summers are mild days in the 80s some 100s but our nights cool off nicely. I really don't need air conditioning so I am now trying to decide if I should install a whole house fan or just an attic fan.  Some people have told me that a whole house fan is noisy. Others tell me that an attic fan is all I need.  I think I may need both.  I'm thinking the whole house fan will draw in the cooler night air to cool the home and the attic fan will keep the attic temp down any time the temp gets to high.


Important factors:
10 foot cathedral ceilings
2 story home

I would like to hear about your experience with these two items.

(post #109518, reply #1 of 17)

John,


Your concern about the attic temperature may be misplaced.  Why do you care what your attic temperature is?  If you have an adequate amount of ceiling insulation, your attic temperature doesn't matter much.  Evidence that attic temperature shortens shingle life is lacking.  Installing an attic fan often draws interior air into the attic through air leaks in the ceiling plane.  If the outdoor temperature is higher than the temperature indoors, that lost indoor air is replaced with infiltrating high-temperature air that enters through cracks lower in the building.  If, in fact, you have low levels of ceiling insulation, then the solution is to install insulation (and perform air sealing of your ceiling), not to install an attic fan.

(post #109518, reply #2 of 17)

HOLLADAYM is right about the attic fan - Better insulation and/or passive ventilation is probably a much better option.

Whole house fans sure can be nice on that first spring day when the air is really fresh and you want to air out the house.

But if you get 100 degree days, it won't do much for you. Pulling air in at night works for a while, but about 5PM on a hot day it wont do a thing for you.

One of their big drawbacks is poor shutters that leak heated air during the winter.


I was once walking through the forest alone. A tree fell right in front of me -- and I didn't hear it.

(post #109518, reply #3 of 17)

I agree with the other about the attic fans. Good insulation, sealing, and ventalation is better.

Besides when you run the whole house fan it will push all of the hot air out of the attic.

I think that the other people have ignored your comments about it getting cool at night. Now I don't know your area.

But I am in Kansas City and it is the humitidy. So I have air. But, still, about 1/3 of the summer I am able to use the WHF instead of the AC.

Get a belt driven fan. While you will hear it, it is not that noisy. The cost is minimum. So if you later get an AC your expense is not that high.

The only down side is the hole is the ceiling that is hard to insulate. You might want to look at the Tamark (sp?) system. See www.efi.org. But I think that it is a little expensive.

Or build an insulate frame around the fan. And then have an insulated cover that you can put over the fan in the winter.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #109518, reply #5 of 17)

"other people have ignored your comments about it getting cool at night."

I didn't ignore it. but when it's hot, it just hot. If they're talking 100 degrees during the day, the house is going to be hot. Doesn't matter much if the temps are getting down into the 50s at night.

I know the thermal mass of the house will help some, but I can't believe it will overcome that.

I'm going to start a museum where all the work has been done by children. I'll put all the paintings up on refrigerators.

(post #109518, reply #4 of 17)

John,

I had a house, built in 1903, that had no central AC and about half of the windows painted shut. I eventually got all the windows open and installed a central AC. But for the first (and very hot) summer, my experience is that I installed a pair of 1500 cfm gable fans, wired to start together via a thermostat and relay. I installed then on a hinged, insulted plenum I made from plywood and 1" EPS, that could be detached at the top and replaced with an solid insulated panel for winter. On hot days, I would open the basement windows, closed all others on the 1st and 2nd floor (those that would open, that is). The attic access was through a second floor closet. The closet door was louvered, the access door was not. I'd prop open the solid door and let the fans pull air through my basement and up through the house and out the gabel fans. I fiddled with the t-stat setting until I determine that when the attic was 105 degrees or more, I wanted the fans to run. The moving air and cooling effect of the basement made a big difference. Before the fans I had to run the window unit in the BR (I had a single, 5000 btuh window shaker for a 2000 sf house) when outside temps got over 85. With the fans, I was comfortable when outside temps were as high as 90. 95 if it was dry. Between shade and basement concrete, inside temps were 10-15 degrees cooler.


Edited 6/18/2002 11:33:28 AM ET by Tim

(post #109518, reply #6 of 17)

I agree with the replies above and have a few additional comments.


Some people have told me that a whole house fan is noisy.  They can be, but most of the noise if from the close proximity of the bades to the shutters.  If you mount the fan vertically (shaft horizontal) in a plywood duct, you can get the fan far enough away from the ceiling opening, which will quiet it significantly (you may need to motorize the shutter).  It doesn't take much distance to make a big difference, and the woodworking doesn't have to be fancy (curve the outside of the 90 with thin plywood, if you're into it).  Get a two-speed unit; 1200 rpm from 1800 rpm (at the motor) will cut the sound level about in half.  And belt driven will generally be quieter, due to the slower blade speeds.  Also, a larger fan at a slower speed will be quieter than a smaller fan at higher speed for the same air delivery, and will use less energy, all other things being equal.


I'm thinking the whole house fan will draw in the cooler night air to cool the home...  No question.  Just close the windows in the morning, as the outdoors heats up much faster than the interior, and open them when the indoors is as hot or hotter than the outdoors.  The fan only works for you when it's cooler outdoors than indoors.  If it cools nicely at night, you'll be freezing by morning (use a timer).  And make sure the windows are open when you start the fan, or you may pull flue gasses and other nasties into the house, blowing out pilot lights in the process, and overloading the motor (propeller fan loading increases with static pressure).


You also need to provide adequate means for the air exhausted into the attic to get out, unless you mount the fan in an exterior wall (looks terrible, and won't work well if attic is well vented).  If I didn't already have a whole-house fan installed by the previous owner, I'd just get a 20" window fan from Grainger (white plastic, easily installed and removed, advertised to move 7000 cfm, although half that is more realistic), less than $200, and no work involved.  I used to park a 16 inch stand fan in front of an open window at night, on "low" (in a 1200 sf apartment), and be nicely chilled by midnight. 


Attic fans are a waste of money and electricity, and an unnecessary roof penetration, IMHO.  Improve the insulation and passive venting instead. 


Just my first hand experiences, as requested.


 


Be seeing you...

Be seeing you...

(post #109518, reply #7 of 17)

Whole house fan properly sized and installed good and sound investment IMHO especially in moderate heat areas like yours. If the outside air is 120 degrees bringing it in won't help.


Attic fans, according to DoE, seldom pay back for the cost and electricity used. Combination of soffit and ridge vent recommended for attic ventilation. You might want to oversize, but not unbalance, the vents to allow easier breathing by the whole house fan.

(post #109518, reply #8 of 17)

Thank you all for taking the time to voice your opinions and experiences.  It looks to me like the majority of responses feel the attic fan is not such a good idea. I am currently installing the new ceiling joists so I'll be sure not to skimp on the attic insulation as most of you suggested. 


I understand what HOLLADAYM  and Boss Hog are saying about drawing in hot air if its hot outside so I accept that the WHF isn't going to take the place of air conditioning. The most important thing to me is to be able to cool the home in the evenings and prior to bed time when outside temps drops. I think Bill Hartmann makes a good point for my specific situation were the evenings usually cool down quite nicely. In this case the WHF sounds like it could remove the excessive heat from the homes interior and displace the attic heat as well.  The noise of the WHF is still a concern but it sounds like the belt driven fans are fairly quiet. Has anyone else setup a WHF like TDKPE suggests in reply #7?  I like the idea of setting the fan back a little to reduce noise but I wouldn't want to compromise efficiency.  In regard to enough open space to allow the WHF to push air out, I have a rear gable vent aprox3'x3' and a front gable vent aprox 6'x3' so I'm thinking this should be adequate to allow the air to vent to the outdoors.


 

(post #109518, reply #9 of 17)

We live in Northern California in the foothills outside the
Valley.  We installed a whole house fan and don't use the air conditioner much any more.  Our electric bill has dropped 25% and we are very happy.   We have high 10/12 foor ceilings with fans.   The house is 86 degrees on a 100 plus day when we get home.  we eat on the East side out side. at around 7:30 to 8pm we start the whole house fan and the temp in the house drops about 10 to 15 degrees in 45 minutes.  


We used the FANMAN out of Sacramento ad are very happy with it all.  I woul suggest looking at his fan. we have friends who used a HD fan and have replaced with FANMAN's unit. his unit has much less noise than others.


I have no relationship with the FANMAN at all.


 


 


 

(post #109518, reply #10 of 17)

John,


   Have you looked at the WHF sold by Tamarack (HV 1000) ? It is a little pricey but very quiet and efficient. We have one in the uppermost ceiling above the stairwell and it does exhaust the hottest inside air. House stays comfortable until about 90 outside.


   J.

(post #109518, reply #11 of 17)

Thanks again to everyone for the advice.


KERRY2131 do you know the make of the WHF you had Fanman install.  I found the phone number to Fanman in Sac so I'll give him a call (916 332-1085) Do you know if he designs the fan or he just installs it?


 JALDEN63 I looked at the Tamtech 1000 fan at http://www.tamtech.com and it looks pretty impressive. Have you found the fan doors operate well (without problems)?   Can you hear the fan running and if so how loud is it.  I'm looking for something to compare the noise level to, do you have to turn up the TV volume when the fan is on?  Do you think the additional (apox 3x an ordinary WHF) cost is worth it?


 


John 

(post #109518, reply #12 of 17)

John,


   I have had the unit for 3 years and so far it has been reliable. I can hear it run but it is hard to quantify. It is quieter than my BIL's type w/ the louvers.(HD I think). In my situation it is on the flat of a cathedrial ceiling in a large open room. Does not whine or make an obnoxious noise but you can hear air move. I would buy one again if that means anything. I have also read in this forum about wiring them to a relay connected to your smoke alarms. A little too late for me. You should also give consideration to smoke detector locations in relation to any WHF.


   J.

(post #109518, reply #13 of 17)

Your input does help.  Sounds like the unit is worth the added cost when considering noise, reliability and ease of installation.


I'll look for the posts on the smoke detector / WHF electrical connection.  If I understand the concept it would to be to shut down the WHF in case of a fire?


What's the deal with smoke detector location? Is the idea to keep the smoke detector away from the air intake path or to put into the air path?


 


John

(post #109518, reply #14 of 17)

John,


  My understanding is to not pull air and make a fire (God forbid) burn faster.Fire depts want fires contained to buy time.Minutes count. Smoke detectors should be away from the air path so fresh air does dilute trace amounts of smoke. I was thinking of starting a thread on draft blocks because I have not seen it getting much attention. Anyone?


   J.

(post #109518, reply #16 of 17)

FanMan buys the unit from someone.  If you want, I can check the manufacture of the unit.  They are not cheap $400 to buy the unit.   They are real up front with you.   No ####.   The high speed in not noise but in not quite.  We go to sleep with it on high and the low speed is very quite.  We love it. 


In the moring I can get the house 2 to 3 degrees lower by running it for 20 minutes.  


    

(post #109518, reply #17 of 17)

On the fire safety side I think that it wouldn't be too difficult to rig a relay on the smoke detector circuit to disconnect the whole house fan. Even if you don't go this far mixing in a few photocell models with the cheaper ionizing models will increase overall safety.

(post #109518, reply #15 of 17)

Since you are doing RFH, here's another option to look into. Run some PEX into the walls in certain rooms so that later, if you ever wish, you can hook up this kind of A/C: http://www.bio-radiant.com/ and click on the Hydro-Air link. There are other manufacturers, too, if you want another link. Run a supply line, a return line, and a condensate line. At least they'd be in the walls at little cost. If you are using something like geothermal, getting chilled water would be easy. For other options, less so. Still, it at least gives you a future option.