I own a 2-story colonial with a finished walkout basement, located about 10 miles SE of Philadelphia, PA. The 1st and 2nd floor is forced-hot-air heated by a condensing, gas furnace that was installed in September 2010 (replacing an old oil furnace), while the basement zone remains heated by a Thermo-Dynamics HT-110 oil boiler (114,000 BTU/h output), which also supplies the domestic hot water (a typical summer/winter hookup).
The finished basement and laundry room (approx 700 SF total) are heated with 45 feet of finned-tube baseboard, while the adjacent utility room (approx 375 SF) is warmed by the furnace and boiler located there.
I just used an online heat load application that calculated ~ 60,000 BTUH heat loss for the 700 SF finished basement and laundry room – but I don’t know how accurate that is. I’ve read that baseboard radiates ~ 580 BTU/h per linear foot, which would mean the 45 feet of baseboard puts out ~ 26,100 BTU/h… and the basement remains comfortable on the coldest days.
We’re now planning to replace the Thermo-Dynamics HT-110 in order to move from oil to gas as the means of heating the basement and DHW – and while there are only 2 of us living in the house (showering at separate times), we want enough hot water that 2 showers could be taken simultaneously with water to spare and a reasonable hot water recovery rate (for when guests stay over).
I’ve considered several options including: 1) converting the Thermo-Dynamics HT-110 from oil to gas + indirect hot water heater or heat pump hot water heater; 2) condensing boiler + indirect hot water heater; 3) condensing combination boiler (for both heat and DHW); 4) smaller condensing or atmospheric boiler + heat pump hot water heater; and 5) atmospheric boiler + indirect hot water heater.
I’ve talked with two reputable heating companies in my area and have received estimates ranging from X to 4X depending on equipment.
For instance, one company will charge X to convert the Thermo-Dynamics HT-110 to gas and install a 50 gallon indirect hot water heater – and while the other company has suggested more options, its most expensive is about 4X for a condensing boiler (like a Triangle Tube Prestige Excellence or Prestige Solo) + a 50 gallon indirect hot water heater.
However, I recently read that finned-tube baseboard operates best with 180 degree water and condensing boilers are far more efficient with 130 degree water (i.e., finned-tube baseboard radiates only about 250 BTU/h using 130 water and condensing furnaces operate at ~ 85% efficiency with 180 degree water).
Consequently, I think I’ve ruled out a condensing boiler owing to their high initial cost and apparent incompatibility with finned-tube baseboard.
Instead, I’m now thinking about configurations like (but not limited to) the equipment listed below:
1) Burnham P202 gas atmospheric boiler, 27,000 BTU, Electronic Ignition, 81% AFUE + 60 gallon A.O Smith Voltex heat pump hot water heater, 2.4 EF (yipes!!!). Obviously, with this type setup the boiler only heats the basement zone. (Equipment cost about the same as X above.)
2) Buderus CG124 gas atmospheric boiler, 110,000 BTU/h (DOE), Electronic Ignition, 84% AFUE + 40 gallon Triangle Tube Smart indirect water heater, 112,000 BTU/h input. Obviously, with this type setup the boiler heats both the DHW and the basement zone. (Equipment cost about the same as .8 X above.)
I’m looking for the most practical and cost effective approaches to achieving the goals of switching from oil to gas, heating (with finned-tube baseboard) a 700 SF finished basement and laundry room, and having an adequate supply of DHW.
Your ideas and suggestions are welcome and appreciated.
I've just read a recommendation to a similar question regarding the heating of a small baseboard zone where DHW is supplied by an indirect hot water tank.
The person making the recommendation says (in part):
"... low-mass boilers reduce the standby loss factor that can dominate in cycling losses a less than full load (not just short-cycling which is even worse.) The 2-stage Lochinvar Solution series of mid-80s AFUE type low mass copper tube boilers are probably more appropriate to [the required] retrofit than the Lochinvar mod-con. Buffered with an indirect HW heater it'll probably meet/beat the performance of the mod-con + whatever hot water heater he's using... Getting the burner size matched to the actual load is the first critical step on the efficiency path though. You can only reduce cycling losses so far with a buffering strategy. Sizing it correctly to start with pays huge dividends: A 93-95% AFUE mod-con boiler may run at 88-90% when right-sized in the higher-temp radiation situation found in most retrofits, but will only hit 83-84% if it's 3x oversized. (Which is VERY typical.) Similar scaling factors occur with mid & standard-efficiency boilers too."
The Lochnivar Solution is a 2-stage boiler with a copper finned-tube heat exchanger, available in 7 output sizes between 36,900 and 213,200 BTU/h.
Does this sound like a possible solution... and given that my zone's 45 linear feet of baseboard can radiate no more than 26,100 BTU/h, what size unit would be best when used in conjunction with an indirect hot water heater to supply DHW as well as serving as a "buffer," if needed..?
Also, can someone explain how an indirect hot water heater serves as both a buffer and the source of DHW..?