Choosing an LP boiler for new construction.

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Old 03-11-15, 09:12 AM
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Choosing an LP boiler for new construction.

Hi, I'm in a planing stage of a new house construction. It's going to be a two-story with a full basement, around 2k ft², with hot water baseboard heat, liquid propane for fuel. It's in upstate NY. I'm trying to figure out what boiler to get, or a boiler/hot water combi. I researched Takagi, Rinnai, Baxi and some others and can't make up my mind. I'm looking for a high efficiency set up, 95 AFUE if possible. My Heat Loss calculation is attached (sorry, not the best quality).Any suggestions would be greatly appreciated. heat loss.pdf
 
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Old 03-13-15, 06:00 PM
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Take a look at the U.S. boiler Alpine ALP80. It modulates down to 16k. The heat input can be reduced and the DHW input can stay at max.
The best thing is May they will have a zone panel you can program to limit the rpm's per zone.
 
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Old 03-19-15, 05:39 AM
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Thanks! I'll look. I'll need to make sure it'll work with conventional baseboards.
 
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Old 03-27-15, 08:26 AM
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Baseboards are designed for water temperatures in the 180*F range (very hot).

Not a good match for any high efficiency modcon (modulating fire & condensing which requires cool 120*F or so, return water temperatures). Makng water that hot will move any modcon into the 85% or so, range of efficiency.

I would recomend a cheaper & more reliable cast iron boiler, like the Burnham ESC3, 52,000 BTU Output Cast Iron Liquid Propane Boiler. A much better match to your baseboard heat emitters.
 
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Old 03-27-15, 09:14 AM
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Let's say instead that 180F is a TYPICAL SPEC for fin-tube baseboard.

However, if there is enough baseboard installed to provide the proper BTU output at say 130F EWT, then there is no reason that fin-tube baseboard can't be used with modulating system.

With STANDARD OUTPUT baseboard, this usually means that there will not be enough physical room to install as much baseboard as needed. HIGH OUTPUT baseboard would be a good choice here.

That said, if you are replacing a conventional boiler and using the same baseboard that was designed to operate with it, then there is little advantage to installing an expensive mod-con boiler because it won't be operating at low temperature and condensing for a large part of the winter.
 
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Old 03-27-15, 09:20 AM
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just noticed... you said this is NEW CONSTRUCTION, so you have opportunity to 'do it right'.

If you are set on a mod/con, make sure you do the homework and design the heat emitters so that they will output enough BTU on the coldest day of the year in order to meet the heat loss... at 135-140F entering water temperature.

Make sure to account for the fact that the water cools as it passes through the system and add a bit extra baseboard in rooms at the ends of series loops of heating.
 
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Old 03-28-15, 06:03 AM
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Just to add to what NJT stated there is radiation out there that will give you the same heat output the 180f type baseboard gives you with 130f water temp. It does not take up that much more room than you need at 180f radiation.

Also keep in mind if you ever need 180f from standard baseboard, depending of amount of baseboard, you only need it at very cold days. Many, many days out of the winter you need something less than 180f.

To support NJT's comments I know a guy in northern MA that has all coppertube baseboard that heated his home this year with the high limit set to 167F. That means that is the hottest his system water temp achieved. He did not use 180f at all as cold as it got.

To comment on Buffalobillpatr's comment Normally baseboard is designed at 180f but does work at lower temps. In the design mode you can design at any water temp it just means more radiation. Most days out of the year you can operate at lower temps due to heat loss dropping as OD temps increasing. For example a heat loss I did was 79,461 at 11f but at an OD temp of 60f the heat loss was 9,921. Mod/con's do work well with copper tube baseboard due to OD reset and modulation. Even though we may need higher system water temps on colder days we still modulate down the gas input as we get closer to the setpoint temperature. It has been suggested that a mod/con boiler may be operating in the lower half of the input at least half of the heating system if the boiler is properly sized.

If you are not familiar with this yet the Fed's are trying to force new or replacement use of cast iron boilers out of existence by increasing the efficiency high enouh it may not be able to be met.
 
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Old 03-30-15, 09:32 AM
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Old 03-30-15, 07:09 PM
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I like this stuff. Lot's of BTU's at low water temperature.
140f just above condensing @ 4 gpm over 600 btu's per lineal ft, 130f still 516 btu's per lineal ft, condensing. New home this is what I would consider.
I know people heating in the coldest days with less than 170f.
I forget the guys name that used to be in here, trooper maybe you remember him. He had the Revolution and claimed he heated with fin tube at a max of 130f.
Smith HE2
 
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