Log home ... rule out installing a modulating/condensing LP boiler?

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Old 08-18-11, 06:47 PM
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Log home ... rule out installing a modulating/condensing LP boiler?

We bought a used log home last December (did not live in it over winter but kept it at about 55 degrees; moving in this fall). The home is in cold country ... not uncommon to hit -30 degrees several times a year. The home is heated with an old (30 year) propane boiler with circulating water to finned emmitters. There is a total of 80-90 lf of emitters on two zones of on 3/4" copper. The heating bill was very high last winter, so looking at replacing the boiler. The house is 40ft x 24 ft. with a finshed basement and a 1st and 2nd floor.

Question 1: with only 80-90 feet of emitters, am I in the ballpark if I estimate that I have a total emitter output capacity of about 45-50K btu/hr? (at 180 degrees)?

Question 2: If I'm right on question 1, I'm low on emmitter capacity and I should rule out thinking about buying/installing a modulating/condensing boiler because the circulating temp will need to be kept well above 130 degrees to get enough heat out of the emitters?
 
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Old 08-18-11, 07:31 PM
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How well is this home insulated?
 
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Old 08-18-11, 07:32 PM
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Correct.

As discussed recently in another thread, you probably won't see much improvement in your heating costs by just replacing the boiler. You will get more bang for your buck by insulating and air sealing the home first. Could be a challenge with a log home.
 
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Old 08-18-11, 07:32 PM
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How did the heat work at 55f. Did it maintain the heat OK. If so, you have enough radiation. It may be more than required. Do a heat loss and see what you need. That way you can determine water temperatures required for ODR. Than you can make an educated decision on what type boiler to use.
LP is the worst for killing efficiency by oversizing.
 
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Old 08-18-11, 08:10 PM
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Heat kept up fine at 55 degrees through the winter. I never got called with a low temp alarm I kept set at 50. We did spend several weekends at the house with outside temps in the 10 to 20 degree range. House was slow to heat up to 70 degrees but it made it. The old boiler is a Weil-McLean that is 114K BTU ... which appears to be well oversized and a real mismatch for 80-90 feet of emitters.

I did an online heat load which came in around 80-85k btu ... but that does not make sense given the limited emiiter capacity that kept it at 55 degrees all winter with the aquastat at 160 degrees and also was able to heat it up to 70 degrees.

As noted, the home is log constuction. The average size 9" logs. The roof is insulated to R44. Windows are all Andrson double-pane casement with an additional 3rd detachable storm pane intalled. The basement is concrete block with 1in foam on outside. 2 of the basement walls are below grade; the other 2 walls are exposed.
Here's a picture.
 

Last edited by NJT; 08-18-11 at 08:37 PM.
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Old 08-18-11, 09:08 PM
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Here is some data on the propane burned in January and Feb to heat the home to 55 degrees:

Propane btu/gal: 91,330

January burned 11.1 gal/day or about 42k btu/hr
February burned 9 gal/day or about 38k btu/hr
 
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Old 08-19-11, 07:22 AM
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Sounds right, now add lower efficiency due to short cycling and your boiler is grossly over sized. Never makes much sense putting a larger boiler than the connected load. No matter how large the boiler you never get more heat out of the radiation than it can put out.
If you have a 4.5 million btu boiler and 80,000 btu's of radiation you will only get 80k out maximum.
 

Last edited by rbeck; 08-19-11 at 07:38 AM.
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Old 08-19-11, 03:30 PM
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The insulation you mentioned sounds good, but what about the walls? Are they exposed logs on the inside? The logs do not provide very much R-value by themselves.
 
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Old 08-19-11, 04:36 PM
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Have you considered wood burning? They have them that retrofit to the exsisting boiler. There are many brands out there, and I just put a few popular links that I have been browsing.

I have read about them but dont know much about them. Also people are trying to get them banned I believe because of emissions. They do have enviromental reports though.

Outside boilers

Wood Boiler USA About us, How we developed the Outdoor Wood Boiler | Wood Boiler, LLC
Central Boiler - Outdoor Wood Furnaces

If I lived in a semi isolated area I would look into wood burning

May be something to look into. IMO wood may be cheaper .

Buderus makes a nice indoor unit. Tech info you can read here.

Buderus Wood-Fired Boilers | G201 | Hot Water Heating | Wood Heating | Buderus.us

Just say'in....

Mike NJ
 
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Old 08-19-11, 09:47 PM
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Thanks everyone for input.

The logs are exposed inside.

Mike in NJ, thank you for the idea on a wood boiler. I didn't want to complicate the post, but the house already has dual fuel - two boilers, the old Weil-Mclean 114k btu LP boiler and a wood boiler manuafacatured by Kuuma. Unfortunately, my wife suffers from asthma and COPD so, for now we are looking to replace the LP boiler (over 30 years old and oversized) and not use the wood boiler.
 
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