Sizing Radiators

njsteambeginner201

Hi All,
I'm a beginner to steam heat and reading as much as I can about it. I'm trying to size two radiators (one room is missing a radiator, the other has several hairline fractures in it). I used some online calculators, but was hoping someone here could shed some light on my figures.
Thanks!

First Bedroom
10'x10'x8' Bedroom
22sf of windows
2 exterior insulated brick walls facing north and west
Heated living room below, Pitched roof attic insulated above
Online calculators are giving me results of:
737watt or 2515btu calling for a: 19" high, 8 section, 4 tube radiator
This seems small compared to the 19", 12 section, 6 tube radiator that used to be in the room.

Second Bedroom
12'x10'x8' Bedroom
25sf of windows
2 exterior un-insulated brick walls facing south and east
Heated dining room below, Pitched roof attic insulated above
Online calculators are giving me results of:
836watt or 2853btu calling for a: 19" high, 10 section, 4 tube radiator
This also seems small compared to the 19", 18 section, 6 tube radiator that is currently in the room.

EBEBRATT-Ed

I would do heat loss for a few of the rooms where the radiators are good and check those # against the btus of the radiation installed.

For example if you find your other good radiation is 15 % oversized to the heat loss your getting then oversize your replacements the same way.

Otherwise you will have balancing problems

EdTheHeaterMan

You need to know what the original designer had in mind. Was the original installer basing his design on the recommendations of the "Fresh Air Movement" following the Spanish Flu? Was the original design from the later 1940s or 1950s? You want to keep the system in balance with the rest of the structure. otherwise you risk an inability to balance. Follow @EBEBRATT-Ed's advice above.

If the room with the "Proper Size Radiators" has the thermostat, then the rest of the house will overheat because the radiators are oversized. If the thermostat is in a room with the oversized radiation, then the room witht he new radiator will not get enough heat because the burner will stop making steam before that room is up to temperature.