Check on the outside of the house if there is an exhaust vent. (Probably looks like a dryer vent?) It should have a baffle that closes it off when not in use. Sometimes these are missing or stuck open.
If not on the outside, then it might just vent into an attic space. Same thing, look for a baffle that closes. If it does vent directly into the attic, this is not the best situation, especially if you live in humid, not arid climate. Excess moisture exhausted in the attic can cause ceiling and insulation damage.
We had that problem with the outside vent in MN. It was not a micro but a regular vent.
It is not normal. Fix is what Conrad said. But in the meantime cover it on the inside. There is a filter on the bottom of the micro. Take it off as if you are cleaning it. Cover with foil, letting it extend beyond the filter as much as you can and still hook it back on. Once it is on push the foil that is sticking out up to the bottom of the micro.
It will not cut off all the cold air but it helps. We had to do it for several months before it warmed up and the snow melted enough to get someone up on the roof.
Posts: 7017 | Location: North MN & Northern AR | Registered: Oct 01, 2002
Update- I brought this up with the HOA. Apparently there is no baffle/damper with the outside venting. There has never been a year this cold so apparently it has never come up. The HOA board is "looking into options"
I won't hold my breath. I'm just glad it's warming up now.
My microwave is also vented to the outside and like others here, it lets in cold air..even the microwave has had trouble starting when it's been really cold! We've lived in the house for 20 years and never had an issue with the cold before...I guess because it's been exceptionally cold.