Hi ScotKat, I have never used a heat mat, but as I understand it, they,re used for propagation purposes, but I would imagine that they would need to be used in a greenhouse with some heat as well, because they wont give enough heat out to heat the greenhouse, but only to provide some bottom heat for rooting cuttings or seed germination, but they,re quite expensive, two wests and elliott sell them, starting at £31.45 for a mat 10"x14" and uses 15 watts per hour, up to amat 16"x25 at£53.45 and 42 watts per hour and their cheapest thermostat is £54.95. I think you would be better off getting a temperature controlled electric propagator, same company have 1 which includes everything you need to start propagating for £78.60, a much better idea in my opinion, google the above see what you think. derekm.

Derekm it was athought as I do have 3 electric propagators and its to save using those.

I agree with Derek these are expensive and are used for propagation I have a heated greenhouse that is used over the winter to house my collection of South African bulbs I use a 600 watt oil filled radiator and a thermostatic plug to keep the temp around 50/55f also I use 3 ply bubble wrap (about 5 times thicker than standard parcel wrap) to insulate the whole greenhouse which helps to keep heat in. We have a prepaid metre and the greenhouse costs about £3.90 a week to run the bubble wrap plays a massive factor in the costs
My greenhouse is 6X6 ft