Should you install a heat pump or a gas furnace in your garage? While a heat pump may be cheaper it really can't handle the large swings in temperatures as you open and close the garage doors. In my opinion modern heat pumps, while much better than the older version, still do better at maintaining temperatures then getting you there. Also when it gets down below freezing the efficiency really drops. We have been very happy with our centralized propane fed gas furnace. If you go this route be sure you keep flammable vapors away from the furnace. Ours is separated from the work side of the shop and the heat ducted into the space. On days like today you will be glad you installed it!