Replacing boiler and perhaps radiators in small Massachusetts colonial
I have a 2300 square foot colonial, built 1960 in Zone 5A, and I’m looking to replace the boiler with a direct-vent mod/con boiler, with indirect hot water. Goals would be increased efficiency (which isn’t just about saving money), reliability, low maintenance, and retiring the current chimney flue.
Current system is forced hot water through fin tube baseboard (with a couple of recently installed exceptions). Boiler is a gas Weil-McLean that’s probably over 30 years old (spec’d output is 95kBTU/hr), with a separate 40gal gas HWH. Insulation is not great: 2×4 walls with some fiberglass, and I’m about to reinsulate the attic with something like R47 cellulose or foam. New windows. House temperature is decently maintained, but the cold walls make it seem colder than it is. Two fireplaces, one of which we use from time to time. Two showers which are occasionally used at the same time, but the four of us don’t seem to take exorbitant showers. There is a 75gal whirlpool tub which we use once in a blue moon.
Here’s the radiator situation for the three zones. Note that the basement zone is a single run, but the first and second floor zones’ radiators are split into East and West loops.
– Basement: 20′ of baseboard. Wall-to-wall rug was installed that blocks the bottom vent, so not a lot of air gets through them, but the heat from the existing boiler keeps things warm.
– First floor: 37 1/2′ of baseboard, plus a recently-installed kickspace heater.
– Second floor: 45′ of baseboard, plus a small cast iron radiator in a remodeled bathroom (vents blocked because it put out too much heat)
I took last winter’s gas bills and heating degree days, whipped up a spreadsheet (based on a TerryLove.com thread ; I think “Dana” is Dana Dorsett!) and consistently found that the boiler would use 30kBTU/hour to heat my house on a 0 degree F day. As a sanity check, when it was hella cold last winter I checked and found that the current boiler was running less than half of the time.
So, here are my questions:
– Should I consider replacing some of my baseboard with radiators?
– Is there any reason for me to get anything more than the minimum-sized mod/con boiler? Or, should I get a mod/con at all?
– Given the size of the basement baseboard, would putting the basement and first floor on the same zone avoid short-cycle risk?
– Do I need to bump the boiler size for the indirect HWH?
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