Large Steam boilers are generally rated in horsepower. Water boilers have several different btuh ratings, the input, the output, and the most important, "I=B=R" rating (Or "DOE" rating).

The only way to properly size the (Hot water) boiler is to perform a heat loss calc on the house, which takes into account the windows, doors, insulation, etc. and size the radiation to this, then size the boiler to the connected radiation.

The only way to properly size a replacement steam boiler is to size the boiler to the connected radiation, plus a suitable "pickup factor". (Usually about 30%)

To actually answer the original question, ( [Linked Image] ) one boiler horsepower=33,479 btuh.So a 100,000 btuh steam boier could be called a "3 HP boiler". Mostly, though, boilers of this size aren't referred to in "HP", but btuh. You start seeing horsepower used as a descriptive term for boilers when they hit the million btu mark. (A one million btuh boier, would, of course, be a "30 HP" boiler.
www.heatinghelp.com (The "Wall" forum) is the premier place to learn about boilers and heating with water and steam, in general.

Good luck.



[This message has been edited by condenseddave (edited 01-09-2005).]

It's all about integrity.