will it ?

[Gofishleech]

Will a 15,000 btu heater be enough for 8x20ft fish house??

It is a manufactured house that may have decent insulation.

[nluchau]

I would say absolutely. Is the floor insulated? If not you will loose alot of heat and then I would say 15,000 may just get you by. If its insulated all around you should be good to go.

If the floor isn't insulated get a bigger heater or insulate it. I'd personnally rather be too hot than cold. You can always crack a window and probably should anyway if the heater isn't vented.