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Member Posts: 3
Hi I'm a fairly new home owner and my house has a gas boiler with hot water radiators. I have cast iron radiators in all rooms except one. My plumber friend said he will hook up the new radiator, I just have to buy one. Im struggling to figure out what size radiator would be right for the room. Using a btu calculator I think this radiator is correct. Am I wrong? https://www.pexuniverse.com/10-section-4x25-cast-iron-radiator

• Member Posts: 4,005
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Seems too high.

If you give us some more details, maybe one of us can figure it out for you. We need the following information:

How many outside walls in the room?
Square feet of any windows or exterior doors?
Single or double glazed windows?
How thick is the ceiling insulation? If there's a conditioned floor above, it's not important.
How thick is the floor insulation? If there's a conditioned floor below, it's not important.
What is the design temperature for your area or tell us where you live.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab
• Member Posts: 8,576
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Have you tried the SlantFin website calculator?
It seems a little inexact just to calculate the square footage, and one window to arrive at the heat loss.
Room BTU requirements will vary on:
location, and design day,
Length of outside wall, and insulation characteristics,
Length of inside walls.
Ceiling, and floor insulation, if on a slab.—NBC

• Member Posts: 3
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Ok the room is on the second floor of the house with a half finished attic above it. 2 outside walls, both have newer windows, plaster walls im not sure what insulation is behind it. The Room is 9 feet wide, 8 feet high, 13 feet long. Im in west Michigan
• Member Posts: 1,356
edited August 2019
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Here is an example of one of my bedrooms. Keep in mind this is a bedroom with no insulation except for 6" in the attic with two old wood windows with drafty storms, and a exterior door with storm that is drafty too. outside design temp here is 5 and the indoor temp I had set to 72.
• Member Posts: 3
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So is everyone thinking something more like this?