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Radiator Size Weird For Location

I have a radiator on a fully finished porch/sunroom that is hooked into the main system. The radiator gets hot but on days like today where the high is around 25 F, the sunroom only reaches around 50 F and can't be boosted to a comfortable temperature even with a space heater running. The room dimensions are 22ftx9.5ft and 8ft ceiling. There's good insulation in the ceiling, the 10 windows are double paned and all gaps have been caulked/ filled. The current radiator is super small so I'm looking to replace it but I have no idea how to size an appropriate replacement on our current single pipe steam system.
Mad Dog_2


  • Jamie Hall
    Jamie Hall Member Posts: 23,275
    Oh that's cute. What you need to do is do a heat loss calculation for that specific room. Then you can figure the radiator from there -- divide the calculated heat loss in BTUh by 240, and that will give you the "EDR" of the radiator -- then find one the right size. You can buy new, but you can also often find perfectly good ones in scrap yards or the like.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    LandofOzisGoodMad Dog_2
  • bburd
    bburd Member Posts: 912
    The maximum capacity radiator you can use there is limited by the size of the runout (branch pipe) from the steam main. We can help you figure that out.

    Mad Dog_2
  • LandofOzisGood
    LandofOzisGood Member Posts: 2
    The calculcator states this is the heat loss and powerv required based on my particulars. I'm guessing next I need to figure out the length of the pipe back to the boiler? This radiator is on the first pipe coming out by itself and is wrapped in encapsulated asbestos for insulation. 

    Mad Dog_2
  • bburd
    bburd Member Posts: 912
    @LandofOzisGood that heat loss number looks way too low. Where are you located?

    We need the inside diameter of the runout pipe, not the length. It may be stamped on the fittings, or give us the outside diameter and we can figure it out, assuming it is standard steel pipe.

    Mad Dog_2
  • gfrbrookline
    gfrbrookline Member Posts: 753
    My guess is that radiator was sized to keep plants alive over the winter not to heat the space at the same rate as the building. If it is maintaining 50 degrees it is doing what it was designed to do. Even with double paned windows you are still looking at a huge heat sink. You are basically trying to heat a covered porch. Instead of looking at this as a heating problem you might want to bring in a builder to more properly structure and insulate the space and then address the heating concerns if they still exist. If you add a larger radiator you are going to basically heat the space for the amount of time the radiator is receiving steam and radiate the heat back to the environment once the boiler shuts down, you will not see a huge gain in comfort.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,918
    Thats a cutie-pie for sure....  A Shetland Pony for a Draft Horse's 🐎 Job!  Mad Dog 
  • reggi
    reggi Member Posts: 511
    Your location would help and knowing what is located under the room, Crawl Space, open to the basement.. different locations have different flexibility..
    I'll guestimate it.. IT was added on to the house or original but only made to be perhaps a screened in porch that wasn't designed to be a 4 season room..
    I would guess the House Exterior Wall is what this room connects to the House, not framed into the house interior..
    That basically gives you exposure from the roof, 3 exterior walls , ? Crawl space.? unknown insulation if anything,
    the windows are set on what looks like a continuous ledge so again the wall insulation below in the original space must be addressed if it wasn't.. The Wall/Floor gap was filled with canned foam..(  the outside hopefully was addressed) 
    Was all the work and improvements done by the prior owner or do you have hands on time with this room ?? It makes a difference..
    Heating it isn't hard to do... To get to interior house temperatures without large temperature drops between cycles...
    Need much more info..

    One way to get familiar something you know nothing about is to ask a really smart person a really stupid question