heat loss puzzle- help please

[pybyr]

Some of you have far more experience than I at calculating heat loss, so I'd like to request help here-

I pitch in with the upkeep of a former one room schoolhouse that is used for various gatherings-- it's heated only on a "per event" basis.

The cellar has a sectioned off "pump room" that contains an iron jet pump, tankless water heater, etc. That space is 7x7 ft with a 6 ft ceiling. Walls are framed with 2x4s and homasote sheathing, and at least _were_ insulated- though I suspect that rodents have made off with much of the fiberglass. Floor is dirt.

The pump room has been kept from freezing to date by a wall-mounted electric resistance heater with a fan in it. That heating unit is old and decrepit, and I've suggested that we replace it before it fails.

I've also been thinking that perhaps we should choose a new heater that does not rely on a fan- such as this radiant unit:
http://www.mcmaster.com/#1991k77/=43eja3

I'd like to "size" such a heater so that we can be certain that it can keep the room from freezing- but not draw more power than needed.

Can some of you who know your way around heat loss calculations in your sleep please give me some input-- and also, if you can, while you are thinking about it, also a way of then going from Btu/hr to watts with such a radiant heater?

Oh- and while I'm picking the Boiler Room's collective brains- anyone ever run across a product in the nature of an "engine block heater" but instead intended or adaptable to placing on a cast iron jet pump as a "freeze prevention device in case all other heat sources somehow malfunction?"

Thanks!

 

[Nofossil]

You just can't do direct heat loss calculations with the unknown rodent factor. Any reason not to oversize a bit and use a thermostat? You could measure the current draw of the existing heater to at least get a baseline of what you have now for heat input.

You could measure heat rise rates at different outdoor temps (given a known heat input), plot them, and extrapolate the outdoor temp at which there is no rise. From that, you could infer the heat loss. Alternatively, you could just leave the heat on for a lengthy period and see where the temp stabilizes. The delta T between that and outdoor temp gives you heat loss as a function of delta T.

A lot easier with datalogging.

 

[pybyr]

Thanks NoFo-- I can definitely figure out the wattage of what is there- and I did plan to put in a thermostat and relay-- just would like to get a fairly high degree of comfort that the radiant unit will move as much heat per watt, roughly, to the critical parts of the room as the convective unit that's there now.