using heat mat in greenhouse?

[habitat_gardener]

Wondering if anyone in mild-winter climates has used a seed-starting heat mat in the greenhouse. Typical outdoor winter temperatures are 40s at night and 50s days, though we have occasional cold snaps and it has gotten as low as the 20s.

Usually I start my seeds with a small seed-starting mat in the back room on top of the washing machine, which means the whole shebang has to be moved when we do laundry. But this summer a fellow gardener gave me a large heating mat that won't fit in the laundry room, and I was thinking of using it in the greenhouse. We've run an extension cord out there for a fan in the spring and summer, as needed.