Is the WH only used for space heating, or for potable water (i.e., hot water in the house) or both? If both, I hope you are using a heat exchanger rather than looping it through the heaters.
Have you done a heat load analysis to determine how much heat you actually need?
Many WH are in the order of 40-60K BTU, but there are some that are larger (in heating capacity, not necessarily in volume).
My personal opinion, a WH is a poor way to heat space.