My "shop" (which is one walled-off bay of a 3-car garage) is well insulated but still gets cold in the winter. I have a Mitsubishi heat pump installed in it, primarily for A/C during the summer months. That does also help with heating, however, below about 40 °F outside temp (4 C), it doesn't work so well.
In past years I've supplemented with a regular, 1,500W ceramic element space heater like you might use in a bedroom, and that has worked fine, but I'm always worried about dust creating a fire hazard. I thoroughly blow out the unit with an air compressor each fall, and there's never been a problem.
This fall, however, my space heater gave up the ghost, so I upgraded to a 1,500W oil-filled electric radiator. There is no exposed heating element, so no hazard from dust. There is also no forced air fan, so it is absolutely quiet. Of course that's not a big concern in a shop. Anyway, I've been using it about a month now and it works great! I recommend it.
For completeness, this is the unit I bought. Apparently that exact unit is no longer available but there are dozens of units just like it, ostensibly from other manufactures, no doubt all built in the same Chinese factory.
I use one of these, I found it cheaper, about 40us retail, locally:
It heats up the room by heating the oil inside the unit (the oil is inside the unit, you do not need to fill it or refill), no fans so no moving air, it uses less energy and is temperature controlled, great for small rooms.
If it's just a single car garage you can probably get away with a 110 heater. My father uses an electric oil radiator for his machine shop to keep it 50 during the winter, it does the job. Something like This is what he uses.
I'm in the same boat except I own it and it's a 3 car detached, looks like either a 240 ceiling mounted electric, or run gas to it, neither of which my wallet is happy about lol
I am a huge fan of the portable oil filled radiator.
I have one that has a timer and comes on earlier in the am then I get up. I also use a heated mattress pad... the whole bed stays warm... not just where the blanket is.
I will second trying to determine if there are any air leaks. I read somewhere if you add up all of the tiny leaks throughout an average sized home it would be equal to a hole the size of a pizza...
Places that might just need gaskets, caulk or foam... light switches, electrical sockets, baseboards, window frames, anywhere the water pipes enter or leave... grab a candle stick and seal up the room... walk around checking everywhere for a flicker of the flame.
Deal link: Amazon
NOTE: Are you looking for discounts on a specific product? Search for the product in our official Discord Server! We are gearing up for Black Friday and Cyber Monday! Grab the deals before anyone else! Join our Discord Server to get real-time notifications on all deals. We have category-wise Discord channels. Disclaimer: Some deal links on this sub may be affiliated