Two Boilers instead of One???

[Deleted User]

I have a quote for 3K for Laars Minitherm 82% AFUE.

Then I have two quotes in the 8K range for 92% Peerless and Dunkirk units.

Is an extra 10% efficiency worth 5K?

Do the high efficiency units have higher service/maint costs?

Would a Modulating boiler still be worthwhile even though I have a mix of cast iron and aluminum baseboards??

Any other boiler suggestions?

Thanks

[Deleted User]

Two Boilers instead of One???

I have an house in Rochester, NY built in 1895 with a 30 year old 201K BTU Weil McLain Boiler. 50 feet of cast iron basboards on the first floor and 50 feet of aluminum baseboards on the second floor. All Copper piping.

Heating bills last year in excess of $800 month in the winter.

Thermomstat never above 68. 63 at night.

We have an upstairs and a downstairs zone with seperate thermostats and circulators.

New Windows. Furnished attic with insulation. Energy Audi being done in two weeks to look for drafts I am missing.

I am planning on replacing the old boiler.

I have one professional telling me to run a second smaller boiler (50K BTU- Carrier 80%) for the upstairs only. Run this boiler at 180 degrees for the aluminum baseboards and continue to have the old boiler run at 130 degrees for the 1st floor cast iron baseboards.

I then have another professional telling me get rid of the old boiler and put in a 125K (Laars 85%) with zone valves for the entire house.

The single boiler option sounds more economical to me, but I am not a professional. Could having two boilers actaully be a better way to go? Any advice and help would be greatly appreciated.

Thanks
Mike

Guy_6

Choice

You are faced with an interesting choice. Here are my initial thoughts:
1) Two boilers tied in to the system as a whole: Stage the boilers and let the demand determine how many BTUs you throw into the system. In reality, systems are designed for worst case heat loss and that happens only a small amount of the time.

2)Utilize a single modulating boiler. This would keep the piping and controls simpler, while operating off of the "demand" principle.

Joe Brix

With only 100 ft of baseboard

I can't see how you could even use 100K BTU of heat. With such a small load, I can't see bothering with 2 boilers.
If you're talking nat. gas. get a 90% condensing boiler, run it 180° and mix down for the CI BB. Run outdoor reset to run at lower temps in the spring and fall.

[Deleted User]

100K BTU Boiler

It would be great if I could go with 100K boiler but I would be a little nervous of it being undersized for a 2500 sq foot house in a fairly cold snowy part of the country.

Unknown

It's all guesswork

till you run a heatloss on the house and see exctly what size boiler you need . There's a free software program offered by Slant Fin toward the left of this web page ( Free heatloss calcs ) , I think they have a downloadable version also .

Joe Brix

maybe the high bill problem

is under radiation. 100ft of baseboard is only going to put out 80K BTU (Generously using 800 BTU/ft) I would add another zone somewhere if I could so you could run lower boiler temps.

Unknown

Mike

I will agree with the others that running two boilers is sort of overkill. The only thing that has not been discussed in this thread is the objective of the heating system. Is the connected baseboard satisfying the thermostat(s) in a reasonable amount of time? Is the existing boiler short cycling off of the high limit setting while it is operating? The only way you will know if the existing baseboard is enough for the house or if the existing boiler is twice as much as needed is by having a heat loss done of the structure. Everything else will be a wild guess! Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics

U.S. Boiler Co., Inc.

Cliff Brady

Ride the curve

Use outdoor reset tied to your higher temperture radation and use a three way mixing valve for lower temperatures on your low temp radation. This lets your lower temp radiation "ride the curve" of the higher temps outdoor reset. For this stategy I prefer a pump for each zone out of a primary/secondary boiler piping loop.

Definately get a condensing modulating boiler with outdoor reset controls to control the modulation.

Use your coldest months gas bills to figure out your "therms per degree day" gas usage. This will give you a rough upper end of boiler input needed based on you actual current usage. 100kbtu or less boiler input is not out of the question you size house.