Re: Replacing shut off valve on the water main line

Posted by Bamb00zle on 2017/9/13 22:29:19
Dinger, we might be saying much the same thing, but it could help to make sure, to possibly prevent someone from making an expensive mistake installing incorrectly sized steam radiators or boiler.

Certainly, the starting point is a heat loss calculation for the building, adding each room's heat loss on the coldest anticipated day, so the system can meet the most extreme demands. Here's how I'd go about it. For steam heat, I size the individual room radiator BTU/hr for the heat loss of that room, then I total all those radiator loads, add an inefficacy “fudge” factor (say 25%), and that's the boiler size required in BTU/hr output. I'd then round up, if needed, to the larger nearest sized boiler. So, for example, if I calculate say 92,000 BTU/hr total load, I'd use a 100,000 boiler, not a 90,000.

Over-sized radiators for an otherwise adequate sized boiler – steam system, not hot water – will result in rooms with short runs from the boiler getting too hot, and rooms with the longest runs from the boiler heating too little, or not at all.... Steam will condense in the nearer, oversize radiators and never get to the distant radiators at the end of the run.

Over-sizing the entire system, but with matched boiler and radiator capacity, increases inefficiency due to short “on” cycles. It wont be cold, but some efficiency is lost. Of course, if its efficiency you're after steam isn't the best. But as you know many old houses around here have one-pipe steam systems that are tough to convert to hot water, so basically they're stuck with them.

Right sized radiators (BTU/hr), pitched so they drain correctly, with properly functioning radiator air vents, and radiator steam valves left fully opened, along with the right boiler control settings – particularly the pressuretrol – means steam will do well enough.

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