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I have twinned heating units as w1 and w2. The first unit to come on needs to be replaced; but, until then I need to know how to get the system to heat better. The problem is the fan comes on on unit one (even though the heat does not come on on this unit) when the system comes on and unit 2 is heating. Seems like it is diluting the heat by pulling air through a cold system. Would you recommend turning off the fan on unit one? And if so what is the best way on an older Bryant unit? Would it be at the Thermostat?

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This needs considerably more detail. W1 & W2 are not especially helpful descriptions of whatever it is you are using two of. –  Ecnerwal Jan 7 at 17:19
    
Two Bryant heating units twinned thru the same ductwork. –  Rudy Jan 7 at 17:20
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That does not count as more detail. –  Bryce Jan 7 at 21:16
    
Why do you have two heating units instead of a single unit with their combined BTU outputs? –  iLikeDirt Nov 4 at 2:34

2 Answers 2

If they are intended to run together, not alternately, turning one off may cause hot air from the other to flow backward through the other, so you'll get less heat into the house.

Unless (unlikely with an older unit) they are drawing in outside air, the heat put into the house is the same, since the "cold air" moving though one furnace is the inside house air. Since the burner is not working on one unit, you have half the heating capacity you should have. That won't change even if the first unit can be turned off in a manner that does not cause air from the other to backflow through the first.

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generally one unit would heat the house. If the temp drops two degrees in the house the second unit comes on. Hope this helps explain. –  Rudy Jan 7 at 17:38
    
HVAC guy says that I need to replace both units so they will interface properly. I guess either that or find an old unit in good condition. –  Rudy Jan 7 at 17:50
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If that is the only reason the HVAC guys says you need two new units, then what you actually need is a new HVAC guy. He's selling you a line of crap. –  longneck Jan 7 at 18:13
    
That's why I posted on here. One thing I don't understand when the number one unit is on everything is fine but if the number one unit is off the second unit does not heat as well. They are the same units. That is why I thought it may be an airflow problem. I will take your advice on the HVAC guy. –  Rudy Jan 7 at 18:35

Such a setup usually involves a spring-loaded or motor controlled damper specifically to prevent air flowing through a shut-down unit. If you have such a damper then shutting down one unit is perfectly fine.

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