I rent out one of my homes to a couple that is using a space heater in the crawl space.
The heater is a small electric heater with a thermostat that is set on low. My concern is fire more than freezing pipes. Using an extension with an electric heater is not a good idea IMO and they have one heavy duty extension cord with an emergency trip on it which makes me feel a little better about it.
I advised them to just fill up the tub for flushing water and not to worry about the pipes since the pipes are pex tubing and an easy fix if they do bust.
I would think that leaving a faucet drip would be good enough right?
Would you be concerned about using an electric space heater under the house?