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Which LP Gas Boiler for 35k BTU house? (2)

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Posted by Verno Inferno on February 10, 2004 at 20:09:57:

First message did not post - happended to a few other people this past weekend

I would like advise on choosing the most cost effective heating source for a hydronic forced air system at my house on eastern Long Island, NY. It will be a closed loop system connected to a hot water coil in a blower unit. The heat load for the house is 35k BTU. The coil supply temperature should be between 140 to 160 degrees at 4 to 6 GPM and 3/4" inlet & outlet supply. Fuel is limited to propane, pilot should be intermittent. Boiler exhaust can vent approximately 20 feet horizontal terminating through the basement wall 2 feet from a window and 12" above the snow line (PVC pipe?) or 20 feet horizontal through the basement wall then 15 feet vertical exposed outside of house (galvanized type-B double wall?). The house is used only on weekends so there is no demand for domestic hot water during the week. This would only be for heating the house.

I researched several possibilities but each has limits and I could use some help or further suggestions on how to go. The most common brands available locally are Weil McLain, Burnham, Peerless and Slant-Fin. The biggest problem seems to be venting.

Option #1 - Weil McLain CGI-25 LP direct vent (50k BTU input, $950 boiler only). This boiler requires single wall stainless steel venting (such as Saf-T Vent) with a 4 foot exhaust clearance from windows, gas tanks or electric meters. Unfortunately, I can only locate the exhaust vent 2 feet from a window. As an alternative, the CGA-25 (natural draft) uses B-type galvanized vent, has a lower efficiency rating, but is only available with a standing pilot on LP gas models (did not receive price quote and prefer intermittent pilot).

Option # 2 - Peerless PI80 or Munchkin M80 LP direct vent (High Efficiency Modulating 27k to 80k BTU input, $1750 boiler only). This boiler can exhaust 1 foot from a window using PVC vent but is twice as expensive as the Weil McLain and will probably never operate at peak efficiency. Most likely it will operate at only half it's rated output under the most extreme conditions and operate at it's lowest output the remaining time - lower efficiency doesn't substantiate the higher price?

Option # 3 - Hook up a small water heater with intermittent pilot and PVC vent, along with an expansion tank and circulator pump? This seems the least costly initially, but would cost more in the long run to keep the tank water heated until the need for heat. Note - The house has a relatively new electric water heater for domestic use.

Option # 4 - Use an on-demand water heater with a circulator pump? From what I can determine, they are vented directly out the back or side which would not work and the flow rates may not be adequate.

Thanks for the help, sorry if too many details!

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