FROGs-finished rooms over garage are usually problematic because of inadequate insulation and poorly designed HVAC. You have to understand both these issues and tackle your problem from both sides. What can be improved for the best bang for the buck? Improved insulation qualities? Add another supply for additional BTUs? Depending on your location, you can expect opposite problem in cooling.

IMO

I have the same problem at my house. If I were to stay in this house I was planning to put some in floor electric heating in place.

"...we have to keep upstairs thermostat at 70 for the bonus room to stay warm."

I don't think you fully explained the problem. If you set the thermostat to 70, what is the temperature in the bonus room? Do you want to lower the temperature for the upper floor, but keep the bonus room warm?

Hi mike

thanks for responding

y s we have to keep heat at 70 for it to be about 65 in bonus room and I hate having the upstairs so hot

i don't want to put a furnace in for just that room

not sure if I should get a heater yet i don't think I hat would do without the job

ii was looking on line and bib villa spoke about these units that could be installed on wall and has a compressor outside

not sure how that works

also there was mention of blown in insulation in garage ceiling?

what have you opt d to do?

Also we had a guy come out to measure airflow cuz apparently the room is at other end of heating system

we have one vent and one return but room is pretty large with slanted ceilings

not sure if a larger furnace would help or just something added to the specific bonus area????

You have a couple of things working against the bonus room. It is at the end of a long run of duct work, furthest from the furnace, little or no insulation in the garage ceiling, and exterior walls on 2 or 3 sides. That all adds up to a lot of heat loss and little heat going to the room.

You can try adding insulation to the garage ceiling first. Foam insulation would work well. But if the duct work going to the room is undersized, then you will also have to address that.

How large is the room, and how high are the ceilings? You should look into a Mitsubishi (there are other brands) mini split. Not sure how much you want to spend. But it will keep you toasty and you will have independent control of the room temperature. You can then keep the rest of the upper floor at a lower temperature with the bonus room door closed.

a mini split will be a costly expense to solve your problem...if you have deep pockets, then go for it...I certainly would look at insulation upgrades first and ask your HVAC dealer if a larger supply or additional supply is practical..

IMO

Better insulation will help with both heathing in the winter and cooling in the summer, if that's the cause of the problem. You probably also need more airflow to that room.

I'm not a DIYer nor a big fan of home improvement shows but even with a casual interest, I've seen too many programs where time after time, the cause of cold rooms over a garage was unsealed openings, incomplete or improper insulation, and/or the presence of openings to outside air. Having someone pull down the ceiling in a corner of the garage to see what's there can may offer an answer.

The first step in keeping a comfortable temperature in a house is making sure that the inside is reasonably sealed and insulated from the outside. That has nothing to do with the HVAC equipment. That could also be a problem but to me that's the second thing to look at, not the first.

May be a gas/electric fireplace.........electric fireplace is much easier, just plug in.

https://www.homedepot.com/p/Home-Decorators-Collection-Avondale-Grove-70-in-TV-Stand-Infrared-Electric-Fireplace-in-Aged-White-365-187-165-Y/207001081