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I'm at my wits end. I just moved into a new (for me) 2 story house (1998) that has some weird heating issues. The house is about 3200 sqft the upstairs is heated by a furnace located in the attic. its an Amana AMH80453ax 2 stage variable speed gas furnace. there are 4 bedrooms upstairs all supplied by this furnace.

Here is the issue: Our master bedroom is regularly 10 degrees colder than the set thermostat temperature and the rest of the upstairs. BUT not all the time. This is with all the doors open between rooms. A few other important notes -- Our bonus room is on the 2nd floor and is heated by the downstairs unit. This room is regularly 5 degrees warmer than the stated thermostat. The downstairs furnace is a self contained A/C/Furnace outside and the duct work is in the crawl space. I live in Tennessee. Also, based on my amateur analysis the air coming out of the vents upstairs is not very warm and normally "feel" of low volume. I have checked the duct work several times and it seems to be fine without any leaks/ no dampers blocking the flow. Clean filter. The master bedroom is not over the garage or has attic stairs. The windows are the same in this room as the rest of the house.

Does anyone have any thoughts on this?

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    Where is the air return(s) for the upstairs furnace? How are the bedrooms arranged upstairs? A map or diagram would be very helpful. – wallyk Feb 14 '16 at 4:02
  • The upstairs return is in the middle of the hallway right under the stat. I've made a very rough drawing link – stewtenn Feb 15 '16 at 16:51
  • Are both those stairways open? That is, no doors to close them off? – wallyk Feb 15 '16 at 17:51
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Variation of the temperature from room to room that is different from the thermostat is a basic fact of operational behavior. you will have to get used to some variation!!

It is possible to even out the differences by changing how much of the heated air gets to each room. This is usually done by using vent controls on each room to permit more or less air into each space. Sometimes there are also vent pipe dampers or diverters that can be adjusted as well. A balancing exercise is usually an iterative process that takes time and patience.

A well balanced system will only stay that way if the same conditions apply as when the balancing was done. Some of these conditions would include outside air temperature, state of window coverings, whether doors are open, closed or partly ajar and if windows remain in the same state (closed or open).

Note that a system balanced for heating can take an entirely different set of adjustments to optimize for cooling during warmer parts of the year.

So as you can see you could try making small gradual changes in your setup. Try closing off more of the the vents that feed into the area where the thermostat is located and open those in the colder room a bit if not already fully open. Remember - iterative process.

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If the duct work is in the attic, even if it's not obviously leaking, it's still advisable to insulate it. Assuming the Furnace is by the return or further away from the master bedroom, the master bedroom would have the longest run of duct work and the air could easily be cooling down while it's running over to the master bedroom. I would add a bunch of insulation on the sides and top of the duct work and see if that makes a difference.

You could probably check if this is the cause by seeing if the top of the ductwork is noticeably warm, if it is then that heat is dissipating into the air above it.

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