Gable Mounted Attic Fans

[A. Pismo Clam]

Hello All,

Since we do not have the room in our attic [or our hallway] to mount a whole house fan, we have decieded that we should go with one of these fans. Since we are doing this ourselves and very new to this, we are asking for your help, please! Today, we are about 104 degrees by our outdoor thermometer.

Our home faces north. As a consequence the east side of the house gets the sun first. We have two static attic vents, one at each end of the home as well as several vents at the eaves. So here are my questions:

[here's the link] When we mount one of these attic fans should we place it on the east end of the house, bringing in cool air from the west side of the house, or should we mount the fan on the west side of the house, thereby exhausting the hot air already in the attic?

By the way, they have a 2.1 amp PSC attic fan that really sounds great. However, what does "PSC" mean.

Many thanks for taking the time to respond!

Norm & Loretta

[Joseph Meehan]

Do you want to use this as a whole house fan or just an attic fan to try and reduce the heat in an unoccupied attic?

If the first, you have the wrong fan and it will do very little. If the second I suggest that proper passive (no fans) venting is usually far better as there is little difference in real results of a active or passive system, assuming they were both well designed and the passive is maintenance free, energy free and silent.

[Speedy Jim]

A gable mount fan can do a lot to reduce attic temps where sun exposure is a big problem. That reduces the heat transmission into the interior.

While static venting is great, you probably don't have the luxury right now to experiment with it.

Personally, I would mount it to exhaust the hot air. Be sure that all inlets are screened as well as the gable outlet to keep bugs out.

PSC fan is "permanent split capacitor". Refers to the type of motor. They run more efficiently, esp when run at reduced speeds.

You'll need to pick the time you work up in the attic carefully; if hot up there you put yourself at risk working.

Jim

[A. Pismo Clam]

Hi Joe and Jim,

Thanks very much for the prompt reply. In the summer, the sun comes up at 6 AM and sets at 8PM; that's 14 hours of no-shade exposure to the concrete tile on the roof.

Yes! We are attempting to keep the attic as cool as we can, Joe.

Yes Jim, I think that we will just have to wait until November to complete this project. Our local DYI store is offering some of these attic fans now and from what you have said, the "PSC", 14" fan sounds like the one we'll purchase.

Again, thanks for all of your help with this, guys!

Norman

[mm]

I do stuff like this at dawn. If I were sure I wouldn't fall through the "floor", I might start at 2 or 3 in the morning, depending on how long I thought the job would take.

People will probabl say bad things about this, but in this case, I would put a heavy duty plug on the end of the cable that comes with the fan, or something so it would plug into a heavy duty extension cord no longer than necessary, put in the extra wood and four screws or whatever the instructions say, then get the heck out of the attic and plug it in to an outlet on the floor below. If so, then dawn would be early enough to start.

Then the fan will keep it not so hot as before, and when there was a cool day, I'd go up and finish it right.

[Joseph Meehan]

Do you want to keep the attic cool because you want the attic cool, or because you want to protect the roof or because you want to keep the living areas below the attic cool?

For two of the four, passive ventilation along with good insulation works very well. With proper insulation between the attic and living area, there is very little to gain by reducing the attic temperature using power vents and you add operating cost, vibration and maintenance.

[Ken]

Although your suggestion there is little benefit to power venting an attic if the purpose is simply to cool it, many homes have the furnace and air handler installed in the attic. I have such a home, and the impact of keeping the attic temperature lower so as to minimize the impact on the cooling coil can be dramatic. My home has gable ends with a power vent in two gables. There is also another gable for air intake along with several eave vents.

On one summer day I wondered what effect the power vents had on the attic temperature and placed a remote thermometer in the attic so as to observe it with the vents on and off. The temperature was easily lowered in excess of twenty degrees when the vents were turned on. I say easily, because I watched the temperature for only about 30 minutes.

Now twenty degrees might not seem like much, but keep in mind the sheet metal of the furnace/air handler (and the cooling coil inside) along with the metal ductwork are fighting the effort to cool the air inside them. I just thought I would share this fact in case the OP had a similar situation.

[Mark]

There are prevailing winds in most places , from west to east where I live...... I would arranage the fans so that they go with and not against the prevailing wind in your area.

Mark

[Joseph Meehan]

That is why I tried to indicate the differences between cooling the attic and the reason to do so. Your example is one of several very good reasons to want to cool the attic itself. Thanks for helping clarify the subject.

[Al Bundy]

"Joseph Meehan" wrote in news:4OEqg.11329$ [e-mail]:

Hey Joseph:

I don't understand how a fan would not be better. Moving 1600 cfm of super heated air from an attic has got to help. I'll agree it isn't going to drop the indoor temp 5 deg but moving 1600 (or even 1200 accounting for inefficiencies) has got to be a good thing for at least the shingles.

[trader4]

I don't see how choosing the static route is an experiment, vs installing a fan. The basics of static venting are well understood.

And whether they have a gable mounted fan or static venting, half of the project is similar. They need sufficient air intake, preferably at the soffits. From the description given, it;s not clear that this exists. In fact, with a powerful fan, they would need even more intake venting, making that project more work.

Also, I think adding a ridge vent in most cases is no harder and perhaps easier than adding a gable vent.

[Joseph Meehan]

Note that I wrote: ".. there is little difference in real results of a active or passive system..." The difference is just not worth the cost in reliability (if the fan fails then it is blocking the passive vent) cost of the fan, power usage, vibration and noise. Yes even a small decrease would be good, but not enough good to outweigh the cost in most situations.

[Al Bundy]

"Joseph Meehan" wrote in news:i0srg.11592$ [e-mail]:

Now noted that you are speaking of all components over time. Thanks for the reply.

But the home inspector when you sell checks the "Excellent" box for attic ventalation. Impresses the buyer. Some buyers probably even think that means it air conditioned up there :-)