A/C And Heat On Same Circuit? - Electrical - DIY Chatroom Home Improvement Forum

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Old 03-13-2013, 11:13 AM   #1
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A/C and heat on same circuit?

I'm afraid this may be a stupid question but it seems to make sense to me. I bought a duplex, which has three levels. The 2nd and 3rd (which is the attic) floors belong to the same unit, and already have A/C. The air handler for the for this unit is located on the 3rd floor, off from the living space, which will be the 3rd bedroom (there is A/C ductwork for the 3rd floor and in the ceiling of the 2nd floor). The rest of the house has boiler heat, but the 3rd floor is unheated, which I think I'll need to provide if this will be a bedroom. I was going to just add an in-wall electric heater for the 3rd room, and use the wiring that is already there for the air handler. Obviously they couldn't run at the same time but you wouldn't want to run heat and A/C at the same time anyway, so I thought I could just add a switch to send power to either the A/C or the heater. Do you think this will fly? It sounds like cutting corners but makes perfect sense to me (I'm not an electrician though).


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Old 03-13-2013, 11:34 AM   #2
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If you can protect each system with the correct size OCPD, (breakers/fuses) then I see no issue. But the chances you can protect both with the same OCPD is probably impossible.
Also in some cases heat an AC are employed together. Room gets to hot, AC comes on. Room gets to cold, heat comes on.
So be sure and have an HVAC guy come out and help you.
I do not recommend this and i am pretty sure its not allowed.


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Old 03-13-2013, 05:33 PM   #3
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So many questions... how big is the circuit supplying the AHU? what voltage?, how big is this proposed bed room you want to heat? I normally use 10 watts per sq. ft. as a rough for sizing electric heat.
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Old 03-14-2013, 04:09 AM   #4
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Can it be done ? Yes.
Can it be done safely - Yes.
Will it fly code wise ? Thats the millon dollar question ?
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Old 03-14-2013, 06:01 AM   #5
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We do this all the time. It's called a non-coincidental load. IF you run `em both at the same time, you deserve to trip out the circuit.

BUT you could utilize a single thermostat with a sub-base to change from A/C to heat with an appropriate relay to prevent that from happening.

Life is uncertain -- eat dessert first!!
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Old 03-14-2013, 06:20 AM   #6
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How about other issues with making an attic space a bedroom, such as egress, smoke and fire protection, etc????


Sometimes I feel like if I answer any more questions it is like someone trying to climb over a fence to jump off a bridge and me giving them a boost.
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