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Pondering a New House Project: Ridge Vent Fan

We had our roof re-done on our ranch house about 5 years ago, and added decent soffit venting & a ridge vent. It's a hip-roof, so there are no gables to install additional cooling, like thermostatically controlled fans. Even with all the venting it gets very hot up there, and the house still warms up considerably. I also added a lot of insulation in the attic to minimize the heat flow down, but it can only do so much.

Adding vent fans to a roof with a ridge vent is generally considered a bad idea, because it can screw up the natural flow of cool air from the soffits to the ridge. I figured one way to fix this would be to add fans that forced air out the ridge vents, augmenting the natural flow.

It occured to me that this has to be a moderately common problem, and that somebody must sell such a thing. I've searched for a while, and come up empty. That means I will probably have to invent one from scratch.

The ridge vent is only accessable up between the rafters, so if I want to park a fan up close, it will be limited to ~ 14" in length. Other wise I will have a LOT of ducting to do. I've been think that something like one of these would be good:

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I don't want to blow the ridge vent loose, so I may need to throttle back on the speed. These typically use shaded pole motors, so an SCR speed control will work. A thermostatically controlled relay, and I should be in business. All it will take is many hours up in the attic doing wiring & probably a lot of ducting to get the air flow right.

A standard gable fan is rated around 1300 to 1600 cfm. I'd need 6 or 8 twelve inch crossflow blowers to match that, but I'm guessing that even 4 would still make a big difference. Of course if I have to back off on the speed, I'll need more.

Another, even crazier, option would be to run a string of these things off one motor. Some sort of line shaft arrangement, maybe with belts to set the speed. Another issue is that the fan & motor(s) will be running in a very hot environment, and I'll need something pretty robust to avoid cooking the thing over time. My old house had a gable fan, and despite regular oiling, it eventually cooked & froze up.

Is this as crazy as it sounds? Anyone got any better ideas, or suggestions to simplify things? I'm at the preliminary musing stage, because I'm still working on several other unfinished house projects. Howwever, it never hurts to think ahead.

Thanks!

Doug White

Reply to
Doug White
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Look up roof ventilators; there's lots of types, passive and wind powered and electric. Soffit vents and ridge vent prevent moisture buildup which aids loose insulation spaces and keeps your woodwork from damp and mildew, but to move air fast enough to prevent a solar oven up there, a fan on a thermostat might be a good addition.

Gables are convenient places for a vent fan, but not the only places.

Reply to
whit3rd

What would be wrong with a whole house fan?

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Wes

Reply to
Wes

The "roof turbine" style vents are common here. Granted they aren't as unobtrusive as a ridge vent, but the do provide better airflow and don't require power. There are some solar powered roof vents available as well, COSTCO happens to be carrying one.

Reply to
Pete C.

On Sat, 31 Jul 2010 21:54:03 GMT, Doug White wrote the following:

Don't do fans, add turbine ventilators. _Free_ to operate, cheap to buy/own, easy to install. I have a gable fan and it costs $$ to operate.

Do you have double/triple-glazed windows, wall insulation, and floor insulation? If not, install until you have all three.

-- To see what is right, and not to do it, is want of courage or of principle. -- Confucius

Reply to
Larry Jaques

As you say, whole-house fans cost money to operate. On the other hand, you can control when they come on (usually with a switch and a thermostat) and high or low speed. Several houses ago, I had two fans installed. One was from house to attic (to exhaust hot air to attic and pull cool air into house), and the other from attic to sky (to cool the attic). They were controlled separately because if the AC was on we usually wanted to move air thru the attic (via soffits and gables up to ridgeline vents or roof fan) independently of house. Also added two turbine ventilators.

In a northern climate, triple-glazed windows get notably less condensation on them than do double glazed. (It's partly a cosmetic issue, because either double or triple glazed windows get much less condensation than single glazed, under a tenth as much.)

BTW, don't recall if this link has been mentioned in this thread yet -

Reply to
James Waldby

On Mon, 2 Aug 2010 06:59:05 +0000 (UTC), James Waldby wrote the following:

I'm afraid you'd have to add turbines for excess airflow from the WWF should you add one. Ridge venting wouldn't EVEN cover it, and unless it's continuous soffit intake (exhaust during WWF operation), it might not cover it there, either.

I'm shivering just thinking about needing triple glazing. ;)

Cool. URL saved!

-- To see what is right, and not to do it, is want of courage or of principle. -- Confucius

Reply to
Larry Jaques

On 8/1/2010 11:59 PM, James Waldby wrote: (...)

Wow! Very cool, thanks!

I see that fan efficiency falls by ~87% when speed doubles. I would not have guessed the cost to be that high.

Very interesting!

--Winston

Reply to
Winston

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