Should I buy 2?

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  #1  
Old 11-18-20, 10:31 AM
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Should I buy 2?

Hi,
I just bought a house with a 40 year old boiler and a leaking hot water heater. The current boiler has an output of 240,000 btu. Itís a 125 year old house so the windows are old. Some insulation has been added but probably not great. Itís 4000 square feet so my rough guess is I need 200,000 btu.

so, I wanted to get a tankless hot water heater, but then I saw the combi boilers. Seems like the perfect solution except the biggest I can find has 185,000 BTUís for heating. So, could I run 2 smaller units? Would both need to have the same btu? Would both need to be combi? Would I pipe them in series or paralell? Iím thinking get one combi unit and one regular?

thanks,
Cody
 
  #2  
Old 11-19-20, 03:21 AM
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You'll need a separate water heater because using a boiler in the summer for DHW is an inefficient, expensive process. No problem using the boiler in the winter, and it's usually piped so incoming CW goes through the boiler coil and then into the HW heater.

As to how much heat is needed, please tell us where the home is located so we can factor in outdoor temperature.
 
  #3  
Old 11-19-20, 11:01 AM
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Folcroftr has three issues, old home with high heat-loss, heating system and DHW capacity.

For DHW he might consider a hybrid DHW system. In heating season, use tankless water circulated with small Taco 007 pump activated by aquastat on direct fired water heater tank aquastat to heat water. This also expands DHW capacity, at lower cost than direct fired.

In summer, with boiler off, direct fire water heater. With high electric heater costs, savings in would significant since only powered in summer.

For heating system would start by learning boiler run time on design temperature day. From that actual BTU can be figured. An easy way is outlined in Doughess posts, starting with #4 in link:

https://www.doityourself.com/forum/b...ing-cycle.html

In my 60 year old home, cost saving have come from reducing heat load with insulation, new windows, etc. Changes to boiler, burners and zoning have helped. Fuel oil cost savings are $2,400 per year. Monthly utility bill shows home to be in top, most efficient group.
 

Last edited by doughess; 11-19-20 at 01:34 PM.
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Old 11-19-20, 02:45 PM
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Great for you, D - I did the same thing in my first home and achieved similar results (FYI - I love a wood or peat fire and briefly experimented with a hydronic fireplace grate, learning there needs to be constant circulation through it even when there's no call for heat - think about that). But we can't begin to help him without additional info, right?
 
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Old 11-19-20, 11:21 PM
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With Folcroftr 40 year old home, looking for ways to reduce heat loss with insulation and windows is great place to start. That will reduce boiler BTU needed.

Finding current 240,000 BTU boiler run time at design temp is key early step. That is real, accurate data. If 20 hours/day at design temp would rush insulation and window.

With lower heat-loss, current boiler may be adequate. The old boilers have very long life, can last for years. Would replace my 60 year old, 86% efficient unit only if it developed irreparable leaks.

In many ways the old are better than new. Have big doors, easy to clean, service and maintain efficiency. New often hard to access, difficult to clean an maintain efficiency. Mine with rectangle steel cabinet had high heat loss to room, Covered sides and top with panels to insulate.

 
 

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