? Whole-House fans for flat roof house?

[DonC]

Hi all,

In every house I've owned, until now, I've installed a whole-house fan. They significantly reduce AC costs and make for comfortable living. Alas, that was while I lived in Michigan in houses that had attics. My typical unit included a twist timer and variable speed motor.

Now we live in southeastern AZ in a condo with a flat built-up roof so a typical attic unit won't work. But we still have frequent cool nights that would we could benefit from.

Anybody here have any experience with WH fans in a similar setting? My research so far has been disappointing -- no variable speed fans and fewer available units : (

Thanks

[willshak]

on 10/6/2007 4:15 PM DonC said the following:

Build a large vented cupola on the roof?

[Reed]

Being in AZ I would consider a swamp (evaporative) cooler. A downdraft model would easily install on a flat roof, and give you cooling when needed, not just at night. I'll bet most of your neighbors have one, (or A/C).

[tbasc]

Condo board is going to have a lot to say about cutting holes and adding electric loads, I should think. Check the rules first. T

[DonC]

Good one. That's on my list of ideas.

[DonC]

Yes we have AC. Some -- but closer to a "few" rather than most -- have swamp coolers but they're simply a form of air cooling limited to about 20 degrees of cooling. When temperature get over 100, 20 degrees isn't enough.

But we're talking about a different animal here. A WH fan "moves" existing cool air supplementing AC at a much, much cheaper cost.

[tom]

A WH fan will move your conditioned air into the great outdoors, won't it? Unless you're talking about a recirculating type fan, which you already have on your AC. Nice weather we're having now, eh? Tom

[tom]

Oops, just re-read your initial post, and will recommend the swamp cooler. The blower will push cooler nighttime air just fine, and save lotsa bucks over the AC during those in-between seasonal warm spells . Tom

[Edwin Pawlowski]

I hope you mean instead of AC, not supplementing. You don't run both at the same time do you?

As for the flat roof, how much space do you have up there above the joists? How much venting? It may be possible, but you may be better off looking at the mushroom cap type of roof ventilator.

[DonC]

A WH fan will allow you to turn your AC off and save a lot of $$$. Are you saying that expensive AC is better than drawing natures cool air through your house?

[DonC]

I guess I wasn't very clear on that. By supplementing I meant using cool air during the night and early morning so as to delay turning the AC on -- if turning it on at all. If the wind is blowing the fan isn't really needed. But that's not usually the case. The fan just gets things moving.

There's 2x12s so I guess that's 11 1/2" +/-. I'm not sure a typical ventilator pulls enough CFM. A typical WH fan is rated 3000 to 4000 CFM.

An example of the economies of a WH fan using Atlanta as an example (The savings would be much greater here -- south of Tucson):

. Operating a properly sized 2-ton air conditioner with a seasonal energy efficiency ratio (SEER) of 10 in Atlanta, Georgia, costs over $250 per cooling season (1,250 hours), based on

8.5¢/kWh, or roughly 20¢ per hour of runtime.

. By contrast, a whole house fan has a motor in the 1/4 to 1/2 hp range, uses 120 to 600 watts, and costs around 1¢ to 5¢ per hour of use.

[willshak]

on 10/7/2007 12:47 AM DonC said the following:

I have a whole house fan and CA, and we use the fan for a number of reasons other than getting cool night air in the house. Did you ever burn something in the kitchen and the whole house smells or fills with smoke? The fan will clean out the smell and smoke in a short time. I let the dog (large Golden Retriever) out one night and she came back in after having an encounter with a skunk. This was 12 AM at night and we spent the next hour washing her in the tub with tomato sauce, tomato soup, ketchup, or anything else we could find with tomatoes in it. The fan cleaned 'most' of the smell out. In the case of having an accessible attic. In the summer, when the attic is about 130º F (I have a black roof with no rafter insulation, but soffit and gable vents), I turn the fan on and blow the hot air out of the attic before going up there, and leave it on while I'm up there. It saves getting drenched with sweat and having to take another shower.

.--

Bill In Hamptonburgh, NY To email, remove the double zeroes after @

[Edwin Pawlowski]

There may be space between the ceiling and the roof. In my last house, it was pitched from about 3 feet+ at the front to 1 foot + at the back. If yours is like that, you can vent the fan into the space by adding enough venting to it. Worth checking out.

[xPosTech]

Over here when I was a kid we had a whole house fan in a window. It's just a small attic unit mounted vertically. They don't have to be centrally located, just on the other side of the house. Open the window the fan is in and open enough others to form a draft (something my grandma tried to stay out of).

At night, we only opened bedroom windows. I still can't sleep with a fan blowing on me. :-)

[DanG]

An exhaust fan will require intake air. This can be as simple as opening a window or using operable louvers opened when the fan unit comes on. The exhaust fan can be mounted in a window, cut into a sidewall, punched through a roof. A roof penetration requires the most to keep it rain tight.

Knock your lights out here:

Roof mount:

Wall mount:

[trader4]

That's what I was thinking too. I'd check around first with any neighbors and see what you can find out regarding anything similar that has been done and how it got approved. Unless this has been done before, you may find that you are going to have a tough time convincing a condo board to OK cutting big holes in a flat roof for a fan.

[DonC]

Nice thought but there is only the width of a 2x12 : ( IIRC the fans require at least 2 clear feet above the fan blades. The fans I previously installed had 4 to 8+ feet thanks to the pitched roofs.

[DonC]

A typical WH fan is 24" to 36" square and move 3200 to 7000 CFM.

Link to WH fans:

[DonC]

Good stuff! Variable speed too! Only negative I see off-hand is the price. The roof top unit I'd need would run about $450 + shipping. I'd also need a speed controller ($20?) -- they've discontinued offering them! And shutters, ductwork and roof curb. But it's certainly doable.

Thanks

[DonC]

Condo has no control re what I do with my roof. They're limited to control of exterior architecture, exterior paint colors and landscaping. THANK GOD! We have no condo Nazis here : )