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I have a room that I use a a guest bedroom in our home. As we don't have guests all the time, we keep the door closed. This room has three exterior walls, and one wall is probably about 70% windows.

This room is always much hotter or colder than the rest of the house, depending on the season. Currently, it's about 35F outside, and measuring the temperature of the walls and objects in the room shows the room is about 48F. The rest of the house is about 67F, and a bedroom just on the other side of the wall measures at 65F.

So this room is currently almost 20 degrees colder than the next room over.

I've had a blower test done, and the insulation and sealing came out OK. Our furnace works fine, but this room is all the way at the end of the ductwork. There's actually two ducts in this room (every other bedroom only has one), with one being just a branch of the ductwork going to the "primary" duct (the one near the window).

I have a ~17 year old single stage forced air gas furnace and air handler, it's oversized for the home, and has no trouble blowing heat around elsewhere.

I'm hesitant to throw more money at unnecessary HVAC inspections, but am willing to try to get someone to come look at this and maybe help solve the problem. I'm looking for recommendations of what to ask someone to look for, or anything I can look for myself - I've tried looking for "leaks" in the duct in the attic, but I couldn't find anything obvious.

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    3 outside walls & a lot of glass… I'd be looking at the insulation values first.
    – Tetsujin
    Nov 30, 2023 at 10:01
  • If you have that many windows, maybe upgrade to double or triple pain glass.
    – cybernard
    Nov 30, 2023 at 15:26

3 Answers 3

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The reason for the temp. differential is in your question.

3 outside walls = more area affected by outside temperatures.

windows = poor thermal resistance.

End of the forced air run = less volume, more temp drop/ increase from the source.

You close the door = reduced circulation

It is about the perfect storm for a room to be a different temp than the rest of the house.

The best and easiest/ cheapest thing you can do is leave the door open. Then look into thermal curtains for the windows. If that doesn't get you acceptable results, consider looking into an additional return in the room to help circulate the air for a better exchange. Also a duct fan will help pull more air into the room.

I had a room in my own home very similar. I added the duct fan for an improvement, but the addition of a return did a much better job of evening out the temp.

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Our tract house has adjustable restrictors on all the ducts in the house. If in heating season we have one room that is too cold and the restrictor is open full on the duct in that room, we increase flow by increasing the restriction in nearby rooms to raise the pressure in the ductwork and thereby increase the flow rate into the room which is too cool.

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Just buy a pyrometer ($20-30). Wait for a cold day, make the air inside the room warm enough, and search for cold spots.

A way to check if your windows have poor thermal resistance is plastic film. Just buy film and cover inside (maybe outside too). If you feel a big difference, then replace the windows.

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