Usually the type of heat is very clear once you get to the house. Sometimes this is documented on our property description and some times it is not.
If having a certain type of heat is extremely important do you it is definitely worth asking on the phone to find out what kind of heating the property has before seeing the property.
Generally you can tell with a quick visual inspection if a furnace is gas or electric and / or if you are dealing with boilers or electric base boards or forced air.
Forced air has duct work coming from it.
A boiler has pipes coming from it.
An electric unit has large electric wires coming to it.
A gas unit thick iron black painted pipe coming to it.