Timed switch rating for whole house fan

Old 07-06-14, 12:31 AM
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Timed switch rating for whole house fan

Hello. Can someone help me figure out the programmable timer electrical rating that I would need to control the motor whose label appears in the photo below?

Why do I want to do this:

This the motor for a whole house fan venting into attic. I want to put a timer on the fan so that it comes on by itself for a couple of hours, say 3-5am to cool the house when the temperature differential between indoor and outdoor is significant. There is little point turning it on early in the evening as the temperature differential is small and not worth the fan energy consumption and noise.

I also measured the fanís electrical consumption using my utilityís main electricity meter and it came in at 550 watts.

So nothing makes sense to me. The label says 8.29 Amps which should work out to 8.29A x 115V = 953 watts. So that would be 953 watts / 746 W/HP = 1.28 HP. Yet the label seems to show .28 HP

What am I getting wrong?
Old 07-06-14, 01:52 PM
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Call the manufacturer.

Magnetek, Inc.
N49 W13650 Campbell Drive
Menomonee Falls, WI 53051
Phone: 262-783-3500
Toll-Free: 800-288-8178
Fax: 800-298-3503
Old 07-06-14, 02:14 PM
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I'm guessing that that might be the starting amps? Looking at other similar motors, they draw around 3 amps for 1/4 HP

Btw...I don't think Magnetek does motors anymore, looks like they may have sold off that division?
Old 07-06-14, 02:15 PM
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Not a pro at this, but motors will have a peak draw at start-up, which may be what the label is indicating.

One caution for whole house fans is their use in a home with naturally vented combustion appliances. When that fan comes on, it can backdraft combustion gasses into the house. As long as the combustion appliances are clean and well adjusted you might never know. But if in the middle of the night a burner gets fouled, it can produce a ton of CO and that you do not want backdrafting into your home.

Old 07-06-14, 02:23 PM
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Just a reminder the timer needs to be motor rated in HP. If just a tungsten or resistive rating even if the watts/amps look okay they may not be able to handle an inductive load.
Old 07-06-14, 04:08 PM
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Another issue...you need to have a source of air. Normally with whole house fans, that means several windows or a couple of doors. Are you going to be awake to open them at 3AM?

I spent an otherwise lovely evening help a woman clean up her living room when she forgot the fireplace damper was open and flipped on the fan before opening any doors or windows. Fine ash everywhere. Uughhh.

Btw...an exact watts to HP conversion isn't really possible. That's a mathematical/theoretical figure, not real life. It doesn't account for friction and electrical losses.

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