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How to rig up an intake fan to a thermostat/temp switch?
Old 08-20-2007, 11:16 PM   #1
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How to rig up an intake fan to a thermostat/temp switch?

I'd like to set up a system in my basement that puts this old centrifugal fan I have laying around to good use (700 cfm, super quiet)


I'd like to find a thermostat or temp control switch that can turn this fan on at say, 70 degrees outside air (need a probe, i assume?). When it kicks on, the fan will intake fresh outside air (usually at night during the summer) until that intake air is warmer than 70 degrees. I think this will reduce our summer cooling bills...as we aren't on top of things enough to go around opening windows and turning on fans when the summer nights dip into the 60's...


How can I do this cheaply and safely? I assume a regular thermostat(digital?) might work, but I'd need some sort of relay and or transformer? Any detailed info/links would be super!!
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Old 08-20-2007, 11:42 PM   #2
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A standard thermostat should work, because it would be similar to a furnace blower. And yes, I believe you'd need a relay in there somewhere. If you know any HVAC guys or electricians, they'd be able to tell you exactly how to do it.

Heck, if you know them well enough, they'd probably come over 'after hours' and hook it up for you for the cost of a couple of cold adult beverages! (that's worked for me a few times!)
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Old 08-21-2007, 04:06 AM   #3
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if you need a probe you can get a line voltage white rodgers temperature controller
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Old 08-21-2007, 07:07 AM   #4
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I don't think you will see any benefit to this system without a lot of additional expense.

First, if you pull outside air in, you will need an outlet for house air to escape to get the full benefit of the fan.
Then you need dampers to close off the system when the AC runs to avoid leakage into the conditioned space and bug screens to keep the critters out.

Now here's the killer, while you are pulling in outside air you are also pulling in additional moisture which your AC unit will have to remove during the day and this is the expensive part of running an AC unit. When the AC starts running the first thing that happens is moisture condensation and very little cooling until the house air is dried out.

The expensive part of air conditioning is the condensation of moisture, the nice dry air in the house is something you want to preserve.
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Old 08-21-2007, 07:28 AM   #5
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Quote:
Originally Posted by UncleHoney View Post
I don't think you will see any benefit to this system without a lot of additional expense.

First, if you pull outside air in, you will need an outlet for house air to escape to get the full benefit of the fan.
Then you need dampers to close off the system when the AC runs to avoid leakage into the conditioned space and bug screens to keep the critters out.

Now here's the killer, while you are pulling in outside air you are also pulling in additional moisture which your AC unit will have to remove during the day and this is the expensive part of running an AC unit. When the AC starts running the first thing that happens is moisture condensation and very little cooling until the house air is dried out.

The expensive part of air conditioning is the condensation of moisture, the nice dry air in the house is something you want to preserve.
Hmm....

I didnt think it'd be THAT much worse than opening the windows at night, which we already do if we remember....just figured it'd be quicker. The fan itself has a damper integrated into the design...so that' nice

As far as an outlet for the air, I ASSumed an open window or 2 should do the trick....? the rated cfm of the fan might not be met, but again I'd assume it'd be close?? It's a 750 cfm fan if I recall...

Soooooo....maybe back to the drawing board....or MAYBE a thermostat/humidistat?

Thanks for the thoughts to ponder
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Old 08-21-2007, 08:14 AM   #6
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Quote:
Originally Posted by thefed View Post
I assume a regular thermostat(digital?) might work, but I'd need some sort of relay and or transformer? Any detailed info/links would be super!!
From an electrical standpoint, what you need is a thermostatic switch designed for an attic fan (Home Depot). This can carry the amperage without a relay.

Re the air flow, don't pull the air through a basement, as it will quickly get wet from the condensate. Pulling outside air through a house is pretty standard here in the Midwest with a whole house fan, which discharges through the roof vents. I do this using box fans in the windows and only use AC a couple days a year.
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Old 08-21-2007, 11:30 AM   #7
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Quote:
Originally Posted by travelover View Post
From an electrical standpoint, what you need is a thermostatic switch designed for an attic fan (Home Depot). This can carry the amperage without a relay.

Re the air flow, don't pull the air through a basement, as it will quickly get wet from the condensate. Pulling outside air through a house is pretty standard here in the Midwest with a whole house fan, which discharges through the roof vents. I do this using box fans in the windows and only use AC a couple days a year.
Yeah, that's it a thermostatic switch. I was looking at them a few years ago for my workshop...but it got put on the back burner.

Re: Box fans in the windows. We have always had a large box fan permanently mounted in the window in our utility room at the far rear of the house. We have it blowing out, and we open various windows near the front of the house to draw the cool air in...from the shaded side of the house. If it starts getting too warm and/or humid, we close the windows and turn on a small window air conditioner. We close the utility room door and let the fan continue to draw air through the crawl space to keep the temp down in the utility room.

Our neighbor has the whole house fan mounted to exhaust through the attic/roof vents.
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