^^^^^ this^^^°

We use a Big Buddy Mr Heater at the hunting cabin for taking the chill off if it ain't cold enough to start up the oil space heater. It does a good job for temporary heating. We generally have it connected to an outside 30 gal tank; but if only going to run it a short time bottles are convenient.

So here are some numbers to consider.
I lb of propane = 20000 btu/ hr approx.
On high: ( 18000 btu/ hr), it burns 1 lb of propane = 1 bottle/hr, or ~ 16 + hrs using a 20 lb cylinder ( propane cylinders are all filled to 80%max. of capacity, emphasis on max.)
On medium: (8000 btu), you get a little over double the time = 1 bottle > ~2+ hrs or ~ 1 1/2 days out of a 20 lb cylinder.

We always keep windows open utilizing cross ventilation. Depending on how hot and how long you're running the unit, humidity will rise.

We use the Mr Buddy heaters in the wall tents every year , we run them off a propane tank set out side as regulators have more issues then the heater it seems. We do use a separate smoke co2 detector in each tent ( like 20 bucks for a 2 pack at costco). For heating the house during power outages, I have a Champion duel fuel genitor that is plumbed into the house propane tank. It can run my entire house including well and heater and all the freezers in the summer I do have to wait about 45 minutes before I can turn on the A/C but then it has enough power to even run it.

LINK to something like what I use

https://www.championpowerequipment.com/product/76533-3800-watt-dual-fuel-generator/

I run a Mr. Heater 30,000 BTU wall-mounted Blue Flame LP heater in my shop. I've been meaning to install a ceiling mounted LP unit but haven't yet. The Mr. heater has no problem maintaining 55-60 degrees in on the lowest setting.

It's very clean-burning but does put moisture into the air.

This One

I also use a single tank-top Mr. Heater in the fur shed. It's not as clean-burning but gets the job done.

This one.

Humidity isn't always a bad thing if you are in a dry cold area. The sinuses can dry out in such conditions.

Humidity levels are way down in the winter. Having an open-flame LP heater adding moisture to the air in the house would be a benefit. I keep a large, cast iron teapot on the wood stove that does the same thing.

Added moisture in the shop or fur shed, not such a good thing. That's why my shop ceiling unit will have an outside exhaust.

^^^^^^^Good safe option there too.