Most spaces are too small for a full s19 even at low power. Look into urlacher or other space heater models with missing hash boards replaced by air blockers.

I usually advise against an s9 in most cases these days. You will get far fewer sats for your electric dollar. Only a good idea if you need lower outputs, s9 has a 100w minimum with a single hash board in braiins vs 600w single hash board minimum for an s19. (Those numbers may vary a little by submodel but a 6x gives you a fair estimate)

A miner is basically a resister in terms of watts/btu. If you are replacing another resistor based heat an s9 is an improvement. More efficient heat in $/BTU terms will require higher J/TH when you replace it if you want to turn a profit. With heat pump heat I'm profitable with my s19 but not with my s9 for heating my home.

Keep in mind that profitable above accounts for the heat. So my electric bill is higher with miner heat than heat pump heat, but I get enough sats that I end up with more bitcoin than running the heat pump and DCAing those extra dollars I put into the electric bill. That is before accounting for the no KYC premium.

Let me know if you have more questions. This is my second year miner heating. I can also @ in some others I know are more experienced if I can't answer.