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heat loss formula help

bostonbrooke Member Posts: 1
hello i am replacing my old tankless oil burner with a new buderus and inderect super stor

tank and grundfos circulators. i am in an awkward situation due to the fact that my seven year old daughter was diagnosed with leukimia last september and needed a bone marrow transplant so no one is allowed in the house for a year but they said the basement was ok. i am trying to size my boiler properly i measured all of the baseboard heat fins and came up with 203 and was told to multiply by 580 and i came up with 117,740. my house is a 24 year old colonial built by my dad with six zones and is very , very tight and has it's own chimmney vented flue. is this the best way to figure the size boiler that i need and if this is correct what size buderus would i go with?

thanks for the help.


  • meplumber
    meplumber Member Posts: 678
    Not the best way but it will work.

    It is not the best way, but in your unusual circumstance it should work.

    One piece of advice.  Multiplying by 580 works if your boiler ran at 180 deg. some of the older boilers opreated and were designed for 200 deg.  If you have any idea as to the temperature that your old boiler ran at, then we could help you fine tune your number.  Also if you posted pictures of the baseboard, then we might could narrow it down further.

    Good Luck to you and your daughter.  Thoughts and prayers are with you.
  • Joseph_4
    Joseph_4 Member Posts: 275
    you should add a pick up factor


       You should add a pickup factor of 15% to the 117,740. It will come to 135,401. On a boiler selection chart the 117,740 would be your heating capacity colomn. The net IBR subtracts 15% for that pickup factor.

    real way to do it is measure rooms and windows, but if your comfortable as your radiators/baseboards are. then adding the counting the footage of baseboard and multiplying by 580 (take into account what my friend "meplumber" said cause its correct) plus multiplying that figure by 15% will work fine.

    Prayers for your daughter and family.

    Be well,

  • Mac_R
    Mac_R Member Posts: 117

    My I suggest using a Buderus indirect tank.  If you are using the Logamatic 2107 boiler control you might have trouble setting the temp for the indirect because of the location of the sensing probe.  I have been told horror stories about using non Buderus tanks with the 2107.  Trust me the 2107 with the BFU and the circulator set to constant run  your house has never been so comfortable. 

    Usually the supply house you are getting it from or the person who is installing it can do a heat loss for you.  just measure the perimeter of the house, windows, doors, and include amount of insulation in the walls and attic, direction the house is sitting and you should be fine.
  • carl_nh
    carl_nh Member Posts: 27
    Buderus Sizing

    When I did my calcuations for S. NH area -5 Deg for our 2800SF cape, and my heating contractor did the same we ended up at 65-75KBTU - its a tight house remodeled and insulated well in 96. We have 150' of slant fin BB, roughly 50' per zone 3 zones plus DHW with the ST160 tank.

    We installed the smallest Buderus G125-21BE a 72K 90.7% efficient oil boiler unit along with the ST160 stacked tank. This replaced a pin type boiler with tankless DHW. Our old system was using 900 gal per year and now we use 500 gal. total.

    There are a number of on line heat loss calculators you can use to determine what you will need, but for a "tight" house, and 200' of BB I would use 500TU/foot or 100,000 BTU. The other aspect is the DHW requirements may be higher than the house BTU if you have 3-4 people showering etc..

    The other aspect with a colonial is the house layout, sun (southern) exposure, and temperature you want to maintain. For instance, if your location is not aided by the southern facing sun, and you want to maintain 75* in the coldest part of the winter then you may need 110K BTU, but that would be overkill in my opinion. I would look at the

    I would find a contractor and have him/her take a look at your house/boiler and make some suggestions - but definitely look at the G125BE Series from Buderus or the "blue flame" boilers.
  • John Mills_5
    John Mills_5 Member Posts: 952
    Heat Loss

    As Mac said, you need to find out the heat loss of the house to size the boiler. Once you get that figure and add in for the indirect if necessary, that will tell you what size boiler output you need. Knowing the radiation helps on water temp. If you are way over radiated, you can run a lower water temp.

    Didn't Slant/Fin make a free heat loss program? Another site has one you can license for home use for $50.

    But if a dealer is doing this work, I'd expect them to take the measurements and make the calculations. They don't have to come inside, I always measured outside on a whole house calc.
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