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# Size of team boiler for 2300 sqft house 3 floors - contractor said 86,000 output is sufficient;

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Member Posts: 14
1. Size - contractor said: BTU does not matter; really? Current boiler: 225000 input, outpout is 181,000; sqft--533. btu/he - 135,800

Contractor says: it is too much; can use something smaller like 105,000 input; output 86000. this is the boiler that he has available. Contractor said too much btu is like loosing energy.
There are 12 radiators for all 3 floors
hmmm

• Member Posts: 23,544
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Is this steam or hot water? If it's steam, the boiler is sized by adding up the connected radiation and matching that to the boiler. If it's hot water, the boiler is sized by determining the design heat loss of the house -- called a "Manual J" calculation and matching that.

Those are the only valid ways to size a boiler -- and if neither of your guys did that, find someone who will.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 14
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Thanks! none of that is done.
• Member Posts: 22,353
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No good thing comes from oversizing. They may be using the WAG method of 30 btu/ sq ft?
Has the home insulation or envelop been upgraded? If so the heatload would be lower then originally built

The load calc is the map to a successful design.

If it is a hot water system and they are bidding a mod con type boiler, a bit of oversized is not a huge deal as they can be dialed in to the exact load.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 1,899
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It depends if it’s steam or hot water. How much fuel did you use the last 12 months?
• Member Posts: 1,218
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Measuring radiators to calculate Equivalent Direct Radiation (EDR) , plus a typical 33% pick up and piping factor will get the largest size you need. If you have one pipe steam, this is the best choice, typically.
If you have two pipe steam, the radiators can be modified to match the current design heat loss and the boiler sized to the heat loss of the home, plus about 10 to 15% for piping losses. This system configuration would also be a system typically well suited for a modulating burner, however, the expense is probably not worth it in this small of a size.
There are other possibilities for smaller boiler for one pipe steam, but you have to have a true steam expert to set up these systems.

• Member Posts: 8,153
edited December 2022
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You need to know if you have a steam boiler or a hot water boiler. Take a picture of the boiler so we can see the connecting pipes from floor to ceiling. and take more than one. from at least 3 sides.

The EDR method is for steam and the Load calculation method is for Hot Water systems

The "what I happen to have in stock" is the wrong method.

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 7,385
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IF you have a steam boiler and 533’ of radiation, then you’d need a boiler with approximately 170k btus OUTPUT.

The data plate,as well as the boiler spec sheet, will state the amount of connected radiation its size can handle.

As others have mentioned, a steam boiler must be sized to match the connected radiation, not the heat loss of the house.

You need to send that guy packing that tried to sell you that 86k btu boiler - he’s clueless about steam.

Try the contractor locator above or post your locale for a recommendation.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 994
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He's spec'ing out a 86k boiler because that's what he has in the shop and wants to get rid of it. He has it in the shop because he tried to use it on another job and it wasn't big enough so he got stuck with it and now has an opportunity to get rid of it.

Go online and get Burnham heating help booklet. You can get a rough idea of what you need. You can size up the radiators so when dealing with another contractor you have an idea if your being bullxxxxed. It wont have every radiator but at least get you in the ballpark. New contractor will do an EDR calculation and get an exact EDR load on the system.
• Member Posts: 1,218
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Ironman said:

IF you have a steam boiler and 533’ of radiation, then you’d need a boiler with approximately 170k btus OUTPUT.

The data plate,as well as the boiler spec sheet, will state the amount of connected radiation its size can handle.

As others have mentioned, a steam boiler must be sized to match the connected radiation, not the heat loss of the house.

You need to send that guy packing that tried to sell you that 86k btu boiler - he’s clueless about steam.

Try the contractor locator above or post your locale for a recommendation.

If it's one pipe steam this is mostly true. However, with two pipe steam the system usually can be modified to use a boiler that is matched to the current peak heat load. There are 1000's of these systems in New York City and I've been doing these systems for about 15 years here in Chicago. We just applied this same technique to a one pipe system and it is working fine so far... more info. to follow coming this spring.
• Member Posts: 22
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have someone who can come and calculate each and every radiator based on height,sections,type to verify what you need. I cant believe someone would tell a client were installing this because it all i have.
• Member Posts: 5,757
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I can
NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
• Member Posts: 14
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Thanks All. This is very very useful. measurements have been done: the 170K BTU is correct for the updated sqft. I did have an oversize boiler because that is what they did back in the days.
• Member Posts: 1,218
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we never found out if it is one pipe steam, two pipe steam or hot water. Each system has very different sizing requirements and possibilities.