Dana, I was hoping you would reply! Thanks for the great info and some actionable suggestions. It looks like I need to find a competent contractor that will install and maintain an NCB-150e, unless there is something with even lower modulation. Their website doesn't find anyone local to southern Maine. I'll tell you a little more detail please.
- 2 Zones - Zone 1 is 15 feet, and upstairs Zone 2 is 25 feet =~ 45 feet.
- 1.5 bath, so only 1 bath/shower. I'm thinking the smaller NCB-150e may be reasonable with low flow?
- We are seasonal, so most of all winter it sits running at 45 degrees, unless we pop in for Holiday, etc.
I can tell you that Baxi Luna 310 hated that situation. Any technology that helps me keep the pipes from freezing in winter is a plus (electrical back-up maybe?).
If you can suggest a contractor, please do. I'm a little worried about not being able to find local service when needed. I want to install this as soon as possible.
The min-fire output of the
NCB-150e in condensing mode is about 11,500 BTU/hr which takes about (/200BTU/ft-hr=) ~55-60' of baseboard to balance at 120F average water temp (AWT), which is where it needs to be to achieve 95% efficiency. If all (15'+25'=) 4
0' of baseboard was operated as one zone it would be possible to suppress short cycling at condensing temperatures, but the biggest zone can't even emit as much as
half the min-fire output.
Taking the shortest zone, to balance perfectly the 15' of baseboard needs to emit 11,500/15'= 767 BTU/hr per foot, which you can get barely get out of the fin tube baseboard at a room temp of 45F- 50F when setting the NCB to it's maximum output temperature of 180F. At that temp there is zero condensing going on, but it won't short cycle. Expect efficiency in the 85-87% range.
With only 40' of baseboard the total heat load has to be less than (40' x 600BTU/ft-hr=) 24,000 BTU/hr, assuming it's possible to heat the place fully even in winter with the existing radiation. Odds are that in reality the load is less than 15,000 BTU/hr 99% of the time or more, even at 70F indoors, and much lower when it's 45-50F indoors. That puts within range of
a pretty-good one ton ducted, or
ductless mini-split heat pump, which would also provide very high efficiency ultra-quiet cooling in the summer season, and INSANELY high heating efficiency during the shoulder seasons. Both Fujitsu and Mitsubishi have a reasonable range of heat pumps in this range. The
state of Maine is currently promoting heat pumps homes currently heated with oil or propane with
rebates through Efficiency Maine, for models that meet sufficient efficiency numbers, many of which appear on
their short list. In competitive bidding a 1 ton Fujitsu -12RLS3H or Mitsubishi -FH12NAH would come in around $4K, all-in, before rebates. A ducted version would come in starting at about $7K, but could be $8K or more depending on how tough it is to route the ducts.
Do
NOT allow any contractor to install the ducts in an attic, above the insulation, at any price! Under the floor in a crawlspace or basement is fine, but ducts and air handler all need to be inside of conditioned space, even if it has to be in soffits under the ceiling level, like this 1.5 ton Fujitsu install out in CA:
Note: This Fujitsu is mounted vertically, with a big filter in the common return below it, and a short supply plenum above with 4 duct runs, all taking up less than 10 square feet of floor area. Most vendors require the mini-duct cassette to be mounted horizontally, which can make it problematic to find suitable places to install it in a low-ceiling cape house. The 10 square foot "utility closet" approach with the Fujitsus works out well in many places.
If it's an open floor plan, heating the main space with ductless wall or floor unit and leaving the doors open to other rooms for freeze control works.
While most mini-splits have a minimum setpoint temperature of 60F, Fujitsu has a "Minimum Heat" mode set to 50F (non-adjustable), and Mistubishi has a "SMART SET" programming mode that allows it to be set to 50F that isn't attainable in it's normal heat mode. The efficiency of these things are quite good even when it's 0F out, if the indoor temp is 50F. It's almost always less than half the cost of heating with a propane boiler, often cheaper than heating with a gas boiler, depending on local utility rates even at an indoor temp of 70F. It's even more efficient at an indoor temp of 50F, since the indoor/outdoor temperature difference is less.
It's not going to heat your water though.
