Welcome! Here are the website rules, as well as some tips for using this forum.

# square feet of water to btu's

Options
Member Posts: 2,124
square fet of steam.... Each sq. ft. of steam is 240 btu....so thta is about 209,000 btu. That being said...you should not size the new boiler off the old one....the system needs a heatloss. Is it steam or hot water. kpc

• Member Posts: 10
Options
Square feet of water to btu's

I have a customer that has a boiler that needs to be replaced I was checking out the rating plate on it and the net I-B-R rating was 870 square feet of water how would you convert that to btu's?
• Member Posts: 1,320
Options
The replacement boiler shuld be...

sized by the heat load method - ONLY if water. If steam, the boiler must be sized using the standing radiation/EDR method - NOT via heat load calcs.

• Member Posts: 10
Options

Thanks Kevin for the response I have already sized the new boiler by using heat load calculations , I know better than to replace with the same size as the old without doing a heatloss.I am curious though about the old one because it clearly says "water sq. feet 870"
• Options
Seeing as

your curious, the boiler would have been rated at 150BTUs per S/F for water. But remember, an appropriate piping and pick-up factor would be deducted from this for your "Net" rating.

Dave
• Member Posts: 2,398
Options
A broader view if I may

Not to diminish the other fine advice here, there may also be a contradiction in terms.

Dave is correct that one SF of radiation (EDR) will emit 240 BTUH in a 70 degree room at 215 degrees steam temperature. The "150" BTUH per SF number is at a 170 degree average water temperature (say, in at 180, out at 160 or in at 200 out at 150, all the same).

You can reduce that amount by 20 BTUH per 10 degrees difference. Thus you will have 110 BTUH per SF EDR at 150 degree F. AWT, and 30 BTUH per SF EDR at 110 degree AWT.

Now, if you are speaking about boilers, there is another twist. All "steam or water" boilers have dual ratings. When used for steam, the output is less because there is less wetted surface. The top portion of the boiler becomes the steam chest and hence releases rather than absorbs combustion energy in a low pressure boiler. You may well find that a steam boiler converted to a hot water boiler will have 15 to 20 percent more BTU output capacity.

I mention this because, if your boiler is over-sized to begin with, it will be more over-sized once converted.

Each capacity listed should be specific to the application, steam or water.
"If you do not know the answer, say, "I do not know the answer", and you will be correct!"

• Member Posts: 6,688
Options
On all the ones I've seen

the Square Feet rating already had the pickup factor calculated in. The Gross or Output or (nowadays) DOE ratings were figured at the boiler outlet before the pickup was deducted.

Now you can figure just how oversized that old boiler was :-O