Click here to Find a Contractor in your area.
In fairness to all, we don't discuss pricing on the Wall. Thanks for your cooperation.
Need to contact us? Visit

Boiler sizing question

dpeartdpeart Member Posts: 31
So I'm reading and trying to learn this stuff enough to pick someone to replace my boiler.  I ran a couple heat loss calculations on the house.  It has zero attic insulation, zero floor insulation in the crawl space, does have storm windows and 8-10 inch brick walls.  I'm assuming it leaks like a sieve.

I also added up the total EDR for the house (as best as I can) and got 547 x 1.33 = 728MBH which matches the BB14-*-5 boiler in the basement.  It is rated at 705-770MBH.

I then did a heat loss calculation and came up with 240MBH @ 15F, or 303MBH @ 0F.  15F being what VA is rated at.

If I go in and insulate the attic and crawl space, and reduce air infiltration by 50% those numbers drop significantly to 128MHB @ 15F and 162MBH @ 0F.

Now for the sizing question.  Everything I've read here is that you size the boiler to the EDR capacity.  After I install the insulation I don't need that much heating capacity.  Do I still go with a big boiler, replace the radiators with smaller ones so I can go with a smaller boiler?  I've not read anything on what to do when you have more EDR than you need due to improvements you made to the house.




  • JStarJStar Member Posts: 2,668
    Heat loss

    Is this one or two pipe steam? One pipe, you are stuck sizing to the radiators. Two pipe, you can size to the heat loss and meter each radiator down with orifice plates.
    - Joe Starosielec
    [email protected]
  • dpeartdpeart Member Posts: 31
    Two pipe

  • JStarJStar Member Posts: 2,668
    Two pipe

    Well, you're in luck. You can size the orifice plates based on the heat loss of each room. Then, you can size the boiler to the new ratings. This will also allow you to remove all of the thermostatic radiator traps, eliminating costly maintenance and service.
    - Joe Starosielec
    [email protected]
  • Tim_HodgsonTim_Hodgson Member Posts: 59
    Steam Main piping

    Your system piping was probably sized for the connected EDR of the radiators. Remember to size the boiler for the large mains AND the heat loss.

    Best regards,

    Timothy Hodgson
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!