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On legacy boiler replacement
I'm about to replace a very old 400K btuh boiler in my home. 6000 sqft, brick veneer, no insulation, 3 stories front, 4 in back. 45 windows. Cast iron radiators, plastered walls. Perhaps someone here can give me advice.
1. I'm not sure how to size the darn thing, Current boiler is 400K BTUH input (measured). It is sized about right as it holds comfort to about -10F. It is a Bryant tube boiler, likely made in 1904. (I could post a photo, Bryant engineers have no record of their making tube boilers after about 1930). I don't know how to measure BTU out to determine efficiency, but the flame bed is about 6-8 sqft and the flue temp at the diverter is only 110F. This scares me: maybe this thing is very efficient and I'll need a 400K 95% replacement. Maybe I won't save money. OTOH, a conventional heat loss study says to size boiler at 400K.
2. No one seem concerned about mixing iron, copper pipe. Isn't there an issue with dissimalr metals that needs to be addressed? A sacrificial anode perhaps?
3. I'm replacing windows and I'm hoping to get Icynene in the walls (if I can find someone who will do it) and this will cut demand dramatically. Should I get 2 furnaces so that one will be sized for new reduced demand?
4. Someone at Munchkin factory says I need a buffer tank, but the boiler will drive a HUGE thermal mass and will suck low temp return water for a long time. Seems like that's when you wouldn't need a buffer tank.
5. Are there any intelligent residential setback thermostats? I've used several and they're all pretty dumb. EG: they fail to learn cool-down rate and adjust heating restore time properly; they'll fire the boiler 30 minutes before set-back time leaving me with 180 degree radiators for an hour after setback; they don't learn about the thermal mass of the system/building and therefore tend to overshoot the target temperature.
Your thoughts are much appreciated.