Could you provide a picture?

If its a gas heater and the window is right above it, there may be code restrictions about what you can use to replace it. Most gas vents for appliances require significant separation from window openings (at least 12-18" horizontal), although the requirements may differ if the window cannot be opened.

Bruce

Bruce, thank you for responding to my question. I will try to upload a photo from the inside with this comment. I put the yardstick next to it to give a sense of scale. The width of the white brick area under the window is 39 in.

I am less concerned about filling in bricks on the outside now because I found some extra bricks in the garage after I posted the original comment and I think I have enough to do the outside.

But I feel like I really need to educate myself on what the best options are for a replacement, even if I have to wait until spring to do it. I may buy an electric space heater for temporary use in this area.

Was that heater installed by a professional? I'm not an expert on these matter by any means, but in addition to what Bruce said about clearances, I thought gas appliances were supposed to have sediment traps and shutoff valves. Maybe I'm missing something, but I don't see either one in your photo.

As for what to replace it with, I like electric mini-split heat pumps, if they suit your climate. They're quiet, and most can now provide heat down close to zero F. If you have the room to mount the indoor unit above that window, a split should do well for you.

Another option, probably noisier, would be a packaged terminal heat pump. You see these a lot in hotels. You'd have to widen the mounting hole. A PTHP would be about 16" high and 42" wide.

EDIT: After looking at your photo again, I think a PTHP would be tight on width, or might not fit at all.

That was a very untidy and possibly code non-compliant installation, looking at the location, the gas line and the power cord. A gas appliance that vents to the outside can't be placed under an opening window.

I'd have the broken equipment removed, the hole closed by a capable carpenter, and look to install something else somewhere else. Its demise give you the opportunity to put in something better and safer.

Good luck.

Interesting comments. This Dynavent replaced an identical one that was in the house when I bought it 20 years ago. Most likely it or its predecessors had been there for decades, since the house was built in 1952. Not sure about code issues, since the furnace company has not mentioned that to me. I agree that any replacement will be an improvement on this, especially since this one has a metal box on the outside. I am just beginning to hear about Mini Splits, but I don't need additional air conditioning in this area and I have the impression that they are very expensive.

PS, I did find a shutoff valve. It is on the other side of the brick wall on the right side of the picture. There is not enough space above that window to mount another unit. I've pretty much decided to get an electric space heater to get me through the winter while I study the whole situation. If I get this room resolved in a different way, I can use that space heater in my basement laundry room later. The laundry room has always been chilly in the winter, even though the basement is heated. I do appreciate the comments and will be all ears if anyone else has additional ideas. The opposite end of this room is an exterior wall also. There might be something I could do with that, although it currently has a TV armoire and two bookcases covering most of it.

I need to find a motor for my Dvnavent

My Dynavent squells very badly when it gets cold out Is there any way to lubercate the motor or find a replacement motor?

I gave up on Dynavent.  Tried an electric space heater, which was ridiculously ineffective, and returned it. Finally had a new gas space heater installed at the opposite end of the room (where there is no window) and it works great.

I love my Dynavent heater must be able to find a motor some place

Go on Marvair company they are the last of the companies that have any parts, and I believe they may have replacement motors, Bob