Electric space heaters are great for instant localized heat. They can heat up a tiny cabin or a small part of a larger space in a few minutes. While they may seem like the perfect answer to your heating needs, they do have some downsides.
They are a huge fire hazard. They produce so much heat that they can not be aimed too closely towards flammable materials, such as drapes or wood structures. On a boat, this is pretty much the entire structure!
They are also a tipping hazard, which then contributes to the fire hazard problem. If a storm kicks up waves or a wake rolls through, the top heavy heater could fall over and start a fire. Some heaters contain shut off switches if they sense that they have tipped over, which is a very important safety feature, but still no excuse for unsupervised use.
Because of these problems, you should never leave a space heater unattended. If a problem were to occur, you need to be there to rectify it immediately.
We keep two space heaters on board, one from Walmart (we went through three before we found one that worked very well, the others didn't hold up) and one from West Marine.
The West Marine heater works wonderfully! It's called the Cube and uses a ceramic core heater. Its tip sensor works reliably (I actually test them out). If you tip it over about 30 degrees, it will turn off. The Walmart one (Holmes) will keep running after it has fallen completely over.
The Walmart heater was a bit of random luck. I would buy a heater and find that it failed to deliver as promised, then I would buy another heater to come to the same conclusion. This was the fourth heater I bought, so I can't say that any heater will work as they all seem to be different. The Cube from West Marine does seem to be a reliable work horse. It was the first one I bought and it heats so wonderfully that I bought a second as a gift for my sister and that one also heated very well.
If you are going to buy only one electric space heater, I recommend the Cube from West Marine. It is expensive compared to other units, but it is worth every penny when you feel warm and cozy on a cold day!
Electric space heaters are an excellent supplemental source of heat and are very useful to add heat to a localized area. When used in conjunction with the other heat sources aboard, it can create a very comfortable living environment while consuming minimal resources.