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EDR calculation check

JohnBoston Member Posts: 20
edited March 2021 in Gas Heating
I'm in the very early stage of planning/thinking about a basement reno. in a 90 yr old house. To make this work for headroom, I will need to remove the original 3" cast iron feed/return gravity loops and homerun PAP from each radiator to manifolds. (gas boiler)

There is a lot more to consider but I would like to get a sanity check on my EDR calculation to start with.

The radiators are the 5 tube type. There are also 3 in wall radiators that were not an exact match but I'm assuming the #'s are close enough for this purpose. I used this table from Utica.
https://uticaboilers.com/sites/default/files/Radiation Tables.pdf

The boiler is set at 160 which is 130 BTUH per sq ft emission. (Is this the right temp. to use?)

The calculations are attached and here is a summary.

Total EDR 77,178
1st Floor
1. Living room 1 = 7,608 BTUs
2. Living room 2 = 7,608 BTUs
3. Family room 1 = 7,608 BTUs
4. Family room 2 = 8,299 BTUs
5. Dining room = 8,991 BTUs
6. Hall = 7,881 BTUs
7. Kitchen - in wall = 1,170 BTUs
8. Bath - in wall = 910 BTUs
2nd Floor
9. Bedroom 1 = 6,370 BTUs
10. Bedroom 2 = 8,190 BTUs
11. Bedroom 3 = 11,375 BTUs
12. Bath - in wall = 1,170 BTUs

How does this look?



  • Jamie Hall
    Jamie Hall Member Posts: 19,954
    Presumably those BTU figures are converted from the actual radiator EDR values? For a water temp of 160? They look plausible, at least...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JohnBoston
    JohnBoston Member Posts: 20
    Yes - attached are the actual radiator EDR values
  • Your numbers look right on. Keep the supply water temperature high enough to prevent your atmospheric boiler from condensing which looks like what you're doing.

    If, however, you have a condensing boiler, you might consider dropping the supply temperature to the radiators in order to force the boiler to condense which will improve efficiency. This will also reduce the heat output of the radiators, but might still be enough to heat the rooms. Your calculations will tell you.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
  • JohnBoston
    JohnBoston Member Posts: 20

    One follow up question - is 1/2" pex-al-pex homerun to manifolds likely to be sufficient given these EDR values?

    I have seen other posts on here that said - assuming 20 degree design temperature, and at 4 fps, 1/2" pipe would flow at 1.5 gpm and 3/4" would be at 4 gpm. 1 gpm = 10,000btus, 2 gpm = 20,000btus, 3 gpm = 30,000 btus, 4 gpm = 40,000 btus

    So, 1/2" should be sufficient? (assuming I keep the current boiler etc.)
  • Yes, no problem. Even for bedroom 3.
    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
  • JohnBoston
    JohnBoston Member Posts: 20
    Thanks Alan