hot water vs steam radiation sizing?

rhodebump

I am researching adding some hot water heating to a room. I am trying to understand how many new radiators that i would need.

The room is 21' x 32' and has a lot of windows (and poor insulation).
I think it will require 60K BTU of heat in a bad winter night.
According to some of the hot water baseboard units, I see around 600BTU/per foot of radiation

Asking a stupid question, but will this room require 100 feet of baseboard heaters? My impressions of this is that you need a lot more radiation area for hot water vs. steam. Is my impression true?

Thank you so much everybody for educating me.
Phillip

KC_Jones

I think you need to run your heatloss calculations again. 89 btu per sq ft is off the scale high. Half that would seem high to me.

rhodebump

You are right, I found another calculator that seemed much better. Good observations.


Total Heat Loss for 60o F Temp. Diff. = 24,300.48
Total Heat Loss for 70o F Temp. Diff. = 28,674.57
Total Heat Loss for 80o F Temp. Diff. = 32,562.64
Total Heat Loss for 90o F Temp. Diff. = 36,450.72
Total Heat Loss for 100o F Temp. Diff. = 40,338.80

Jamie Hall

I agree with @KC_Jones on your heat loss calculations. One of my outbuildings is about that size, cathedral ceiling, no foundation (it's on piers) and no insulation at all. And gets by well enough on 30K at 0 Fahrenheit.

That said, yes indeed the heating capacity of hot water heat -- of any sort -- is much less, per square foot of effective radiation, than steam. It varies with temperature; someone has a chart, but very roughly it's about 2/3 steam if the water temperature is around 180.

Ironman

ERD = Equivalent Direct Radiation. Radiators are measured by the sq. footage of surface area they have. That is multiplied times 240 to get the btu output for steam or times 150 to get the btu output for hot water @ 170* average water temp.

EBEBRATT-Ed

your heat loss is way off. download the Slant Fin app and use that. 15-20k is probably about right