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View Full Version : OT: Efficieny of Boilers vs Heat Pumps



chefwong
04-21-2010, 06:35 PM
OT: boiler gurus but I have a closed loop mixed system. Some Baseboards are cast iron and some are old school . I do know is CONSIDERBLY cheaper than electric out here in NYC but love to hear your thoughts.

I have a older Pennco Boiler in my 80-100 year old home.
Curious on your thoughts of efficiencies of the heat pumps in ductless systems vs. old school closed loop boiler/hot water systems

http://www.terrylove.com/forums/forumdisplay.php?13-HVAC-Heating-amp-Cooling

Wally Hays
04-22-2010, 12:22 PM
change the boiler. Either Buderus or Viesmann would be my to choices. Get outdoor re-set control with either. Leave the baseboard alone.

Dana
04-22-2010, 03:12 PM
What Wally said (but I like Triangle Tube & Peerless- there are MANY good modulating/condensing boilers out there.) Odds are, if you've upgraded the insulation & air tighness of the building in the past 80-100 years the boiler & radiation is oversized, and never ran better than 70% efficiency on it's best day, with an average AFUE under 60%. A properly sized modulating boiler will cut the heating fuel by at LEAST 25%, and 40% isn't unheard of, and 90%+ efficiency isn't out of the question.

Old-school cast iron radiation is good stuff- much nicer to live with than baseboard convectors or wheezy-breezy heat pumps with tepid-air output. But get a room-by-room heat loss analysis as step-1 with any heating system- your comfort & operating efficiency depend on it. MOST boilers in the northeast are oversized for the true loads, to the detriment of both. (Which is why modulating boilers are preferable- they can be tweaked for higher comfort, which usually means higher efficiency as well.)

Lightwave
04-22-2010, 06:35 PM
Curious on your thoughts of efficiencies of the heat pumps in ductless systems vs. old school closed loop boiler/hot water systems

There's really no contest. The best boiler setup will be no more than 90% efficient. A well designed heat pump will be at least %200 "efficient" in terms of heat generated from power consumed.

Dana
04-23-2010, 09:37 AM
There's really no contest. The best boiler setup will be no more than 90% efficient. A well designed heat pump will be at least %200 "efficient" in terms of heat generated from power consumed.

That's some pretty fuzzy thinking in the real world.

From % of fuel energy delivered to the load point of view a heat pump driven by a combustion-fueled electric grid needs to have a COP of 3 or greater to match a 90% efficient fossil-fired heating system. The average N. American fossil-fired plant sends ~65% of the fuel energy directly up the flue & cooling towers, and and another 6-10% gets eaten up in distribution losses, for a net ~25-30% fuel-to-load efficiency. Nuke fuel-to-load efficiencies are are even worse. The NYC the grid is powered with a preponderance of fossil & nuke plants. Combined-cycle gas plants run about 55-60% efficiency fuel/load though.

A "best boiler setup" with low-temp radiation (radiant floors or celings) can easily average in the ~95-96% range in a well designed system- 90% is the low end of where a mod-con runs, even on old-school radiation (if properly sized & optimized.)

hj
05-01-2010, 03:10 PM
WHAT is "considerably cheaper than electric" out there?
The practicality of a heat pump depends to a great deal on WHAT your temperature range is, and whether you would have to resort to "resistance" supplemental heat in the form of heat strips on the coldest days.
By ductless systems I assume you mean a forced hot air system, and that is a different animal than hot water systems, which by the way are ALL closed loop.