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In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Steam boiler sizing dilemma
Hi folks, I've read every article I can find here and elsewhere and every post on The Wall about boiler sizing at least three times now, but I still feel unsure on my situation.
I've got a choice between a new Burnham IN4 (271 sq ft) and IN5 (358 sq ft).
I calculate I've got 253 EDR of radiator and the pros who've given me quotes get about the same (maybe slightly more). Seems obvious the IN4 is the right choice and was recommended by one contractor I got an estimate from. Everyone else recommends the IN5.
Here's where it seems a little more complicated. This is a two family house and the current boiler (787 sq ft) heated the whole thing. The other unit has disconnected from the system and removed their radiators, plugging most risers in the basement, but there may be one or two plugged up on the third floor, so closed unvented pipes going up the walls.
And there is a lot of main piping, starting out with two branches at 2 1/2" and 3" then branching out more (getting smaller). Maybe 100 feet or more. (Yes there is a T into the main, and no I'm probably not going to spend the extra $1000 to replace it now. It is 8 or 9 feet above the floor, so I'm hoping not too much wet steam gets up there). Maybe this counts as particularly "unusual" piping. (The mains are not well insulated now, but I'd plan to do that especially well if I got the smaller boiler)
Using Dan's suggestion from L.A.S.H. pg75 of increasing the piping-pickup factor to 1.5, that gives (253*240) * 1.5 = 91K BTU, 4K over the DOE capacity of the IN4.
I'm also planning on getting a 45 gallon SuperStor indirect water heater on it, though I understand this shouldn't matter?
If anything, we could reduce the size of radiators since the house is better insulated (it's 1905 construction) and windows are being replaced. But I don't know if that's really going to happen.
Does any of this justify bumping up to the IN5 (358sq ft, 115 DOE heating)? Would that be a more conservative choice to be sure we can fill the mains and radiators (quickly), start up cold (fall/spring), maybe recover from a setback of 5 or 6 degrees? If you needed 92 DOE would you go up to 115 rather than down to 87? Any chance more than a 1.5 pickup should be used?
I'm concerned with being fuel efficient. But we're also pretty concerned about being sure the house heats up when we want it to, and that we don't have to be calling back the professionals a lot to keep tweaking the venting to make it work well.