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Old 01-01-2010, 01:24 PM   #1
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Need help on hooking up a duct fan to thermostat


Have as basic question for probably most of you guys. I mainly heat my house, small 1400 sq. ft. ranch with our wood fireplace insert, fairly centrally located. My problem is our two bedrooms on the west side of the house,(prevailing winds), when my daughter goes to sleep at night, we close her door. I usually go to sleep much later. This in turn, turns her room into an ice box due to the furnace not running.I can have the family room maintained @ 77 degrees, but with her door closed, it gets in the 50's.
What i would like to do is install a ceiling mounted intake and run a duct line to her ceiling and the other bedroom, with an inline duct fan, and run these off a thermostat mounted in the wall of the family room. Such as....when the family room is heated and the thermostat (figured a round Honeywell type), is set at say 70, the fan would kick in and intake the family room heated air into her room, and turn off, when the family room cools down, and the the furnace kicks in. I don't know a ton about hvac, but i do have mech. intuition, just not elec.
I know that fans fun off standard current, and thermostats run on low voltage, so how do i do the transfer? Some sort of transformer? I don't just want hardwire a light switch for power, want to make it Automated.
Would appreciate any help. I assume that this would be wired for the cooling cycle of the thermostat, right?

cold in Wisconsin,
John

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Old 01-01-2010, 01:47 PM   #2
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Need help on hooking up a duct fan to thermostat


Run your furnace fan in the ON position and it will circulate the heat thru the house and solve your problem. Lots of wood burners do that. Does your daughters room have a return air vent? If not then you may want to cut an inch off the bottom of the door so air circulates out of the room better. If your electric rate is under 10 cents/kwh I would buy a 1500 watt Honeywell baseboard heater at HDepot and install it in her room. I am sure she is worth the cost.

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Old 01-01-2010, 01:53 PM   #3
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Need help on hooking up a duct fan to thermostat


I tried that in the past, but never seemed to get much for results, I would rather take the good hot air off the ceiling, because I don't need it in the family room at night. Thanks for the suggestion. yes definitely worth the cost. We did try that as well when she was younger. The electrics have that tinging noise when they start cyclling from the expansion. My wife wasn't thrilled at all from the safety aspect, you know wives. I suggested the oil type heaters, but thats a no go also. This seems to be the most economical, and most advantageous of the heat already being provided, just re-routing it.

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Old 01-01-2010, 01:57 PM   #4
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Need help on hooking up a duct fan to thermostat


If you are going to invent a fan system it will:
1) Be noisy
2)Have to be wired according to an electrical code and be inspected for insurance co reasons
3)Be costly as an electrician should do it
4) Initial cost is high
5) Fan costs $$ to run

You can have an electrician wire up a 120 volt baseboard type wall tstat to your fan.

Costs very little for the baseboard heater to run, is 100% quiet and no fuss to install. I use a couple in my house.
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Old 01-01-2010, 02:03 PM   #5
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Need help on hooking up a duct fan to thermostat


I've already got a fan, a small long squirrel cage type already in a intake box. It's actually very quiet. An where i live, we can pull the permit ourselves, it just needs to pass inspection
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Old 01-01-2010, 02:16 PM   #6
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Need help on hooking up a duct fan to thermostat


If you have never done house wiring before then I would get a electrician to do it to be on the safe side. Saving a few $$ is not worth endangering your family or having a house fire. Electrical inspectors can be very picky and homemade setups they may have a problem with.
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Old 01-01-2010, 02:30 PM   #7
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Need help on hooking up a duct fan to thermostat


I suppose I should give you a little backround. I run my own carpenter contractor company, including roughing, finishing, and have my own shop and build custom cabinets. I have wired my own shop, and cabin up north, and both have passed inspection. I do not however profess to know anything much about the electrical aspect of HVAC low voltage, which is why I am posting this question.
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Old 01-01-2010, 02:35 PM   #8
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Need help on hooking up a duct fan to thermostat


Don't need a low voltage tstat. You can buy a wall thermostat for a 240 volt high wattage permanent baseboard heater and run your 1 hot wire to it and have it break the circuit for your fan. I would draw up a plan of what you plan to do and have it approved by the inspector B4 you do the job. They may not like /approve your idea or approve a DIY fan setup. Same with the insurance company. If they do then you are good to go. Would need the appropriate wire, junctions boxes etc etc. I cannot draw you a plan, just give you the idea.

Last edited by yuri; 01-01-2010 at 02:38 PM.
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Old 01-01-2010, 02:36 PM   #9
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Need help on hooking up a duct fan to thermostat


High voltage thermostat will do what you want. A transformer to run low voltage to a standard thermostat which will pull in a contactor in the fan circuit will do the same with more compents.
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Old 01-01-2010, 02:37 PM   #10
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Need help on hooking up a duct fan to thermostat


not what i am looking for. thanks anyway Yuri. wait a minute, i think i misunderstood your post.now i believe i get it, use half of high voltage system instead of jumping up , or restricting low voltage system.

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Old 01-01-2010, 02:39 PM   #11
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Need help on hooking up a duct fan to thermostat


Its an ok idea.

If that room needs 100 CFM from your central system to keep it warm when the wood stove isn't on.
Figuring that the furnace air temp to that room is 120F, and keeps the room at 70.

If your ceiling area temp in the room with the wood stove is 90F(and your fan is pulling from that 90 area), and the duct loses no heat in the attic. the fan only needs to move 250 CFM into your daughters room. To keep it at 70.

Since you want to do both bedrooms. If they are both the same size. The fan needs to move 500 CFM(bigger, if the rooms need more heat then in my example).

So each room needs a 10" supply duct, and of course the appropriate sized register(based on my example).

Pretty big fan.


They make line voltage cooling thermostats.
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Old 01-01-2010, 02:40 PM   #12
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Need help on hooking up a duct fan to thermostat


I do lots of electric furnaces etc and can make my plan work for you if the inspector allows it. Need a heating tstat.

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Old 01-01-2010, 02:45 PM   #13
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Need help on hooking up a duct fan to thermostat


Yuri, i think I got it figured out.
beenthere thanks for the quick calcs. In that case, maybe I'll just run it to her bedroom. we usually keep the kids doors closed and the other cold bedroom is mine and we keep our door open.

thanks all of you.
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Old 01-01-2010, 02:48 PM   #14
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Need help on hooking up a duct fan to thermostat


http://customer.honeywell.com/Honeywell/UI/Pages/Catalog/ComponentCategory.aspx?Catalog=Homes&Category=Mech anical+Non-Programmable_2035&ChannelID={2EB2F178-20ED-44E0-97FB-CCFB4218DD64}

Thermostat link

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