heating in winter

So I have an in wall DT with fish room in garage. Although the room is closed off to garage and insulated it still gets cooler in the room and my Temp dropsy a few 3 degrees at least in evening. We have not even had a real winter yet so this concerns me. I run a total of 450 watts of heaters in sump and still. Do they have a heater unit yet like the chiller units or a better and larger single heater unit out in the reef world?
75 gallon reef
30 gallon sump