Match your radiator by height, sections, and tube configuration to find the right replacement with confidence.
When replacing a radiator, it’s essential to match the existing heat output. The BTU rating of the current radiator—and the heating requirements of the room—are the most important factors to consider.
By measuring three key elements—height, number of sections, and tube configuration—you can accurately determine the radiator’s heat output in BTUs. If you have an older radiator with dimensions that differ from our current offerings, you can use this helpful resource to find a comparable match: www.oswaldsupply.com.
You can also refer to this chart for additional guidance: Square Feet of Radiation per Section (PDF)
If you don’t have an existing radiator to reference, performing a heat loss calculation will determine the BTU output needed to properly heat the room and help you choose a compatible radiator. Here is a helpful heat loss calulator tool: USE BTU & HEAT LOSS CALCULATOR
Most replacements come down to height, number of sections, and tube configuration.
STEP 1
Measure from the floor to the top of the radiator.
We offer radiators in two heights—19″ and 25″. The taller model provides greater heat output, making it ideal for larger or colder spaces.
Shop Radiators by HeightSTEP 2
More sections means a longer radiator and greater heat output.
Count the repeating vertical sections. More sections means a longer radiator and greater heat output.
Learn About Radiator SectionsSTEP 3
Identify how many columns deep the radiator is—typically 4 tube or 6 tube.
This determines both radiator depth and heating capacity.
Slimmer profile, lower output.
Deeper profile, higher output.
Determines the overall size and replacement category. It also impacts heat output and where the radiator can fit within your space.
Determine the width and total heat output. More sections mean a larger radiator with greater heating capacity.
Determines the depth, style, and BTU output. Different configurations affect both performance and appearance.
Use your room size to estimate how much heat output (BTUs) you need, then match that to a recommended cast iron radiator size.
Tip: Most rooms need 30–40 BTUs per square foot, depending on insulation and climate.
*Results are estimates for informational purposes only. Oswald Supply advises consulting a licensed heating contractor to verify your project's exact heating requirements.
| Room Size | BTUs Needed | Recommended Radiator Size | Best For |
|---|---|---|---|
| 40–60 sq ft | 1,500–2,500 BTU | 4 Tube × 5–6 Sections | Bathrooms / Hallways |
| 60–100 sq ft | 2,500–4,000 BTU | 4 Tube × 7–8 Sections | Small Bedrooms |
| 100–150 sq ft | 4,000–6,000 BTU | 4 Tube × 9–10 Sections | Bedrooms / Offices |
| 150–200 sq ft | 6,000–8,000 BTU | 4 Tube × 11–12 Sections | Medium Bedrooms |
| 200–250 sq ft | 8,000–10,000 BTU | 6 Tube × 10–12 Sections | Kitchens / Dens |
| 250–300 sq ft | 10,000–12,000 BTU | 6 Tube × 12–15 Sections | Living Rooms |
| 300–400 sq ft | 12,000–15,000 BTU | 6 Tube × 15–18 Sections | Large Living Areas |
To calculate the required heat output for your radiator, you will need the dimensions of the room. Our BTU calculator also asks questions about other features in the room, such as the types of glazing and the number of outside walls. Once you know the BTU requirements for the room, you can then choose the number of radiator sections you will need. Explore our BTU Calculator.
This is where you can get a bit creative. For example, if you have a very large room with a high BTU requirement, you might need to get creative. Imagine you don’t have the wall space for a longer radiator, but you do have a large bay window. You could choose the shorter 460mm column radiator which could stand below the windows where furniture won’t be placed. You can then pair these with the taller column radiators which won’t then take up so much wall space.
This depends on how many BTUs are required for the room. Older radiators may be much larger and emit less heat than newer options, so it’s important to base your decision on the required heat output rather than relying on additional heat sources.
When sizing a cast-iron radiator, it’s important to choose a radiator that can heat the room on its own, based on the room’s BTU requirements.
While supplemental heat sources may add warmth, they do not provide the same consistent, reliable heating as a properly sized radiator connected to your home heating system.
For example, a wood-burning stove may produce high heat output, but it takes time to light, build heat, and maintain temperature. A properly sized cast iron radiator delivers steady heat as soon as the heating system turns on.
For the best comfort and performance, always size your radiator to meet the room’s heating needs without relying on an additional heat source.
Choosing a radiator that is too small may leave the room underheated during colder weather, even if you plan to use another heat source occasionally.
No. It is important to match the current radiation. Oversized radiators can cause system issues and reduce efficiency.
These conditions can increase the amount of heat required to keep the room comfortable, so a radiator with slightly higher BTU output can help maintain proper warmth.
If your goal is energy efficiency, the best approach is to choose a cast iron radiator that closely matches the BTU requirements for the room. This helps prevent overheating and avoids wasting energy.
The best radiator size is one that matches your room’s BTU needs as closely as possible.
A well maintained radiator can last anywhere from 15-20 years.
Yes, radiators can be painted, but the type of paint matters. Standard emulsion or gloss paint is not suitable for radiators, as the heat causes it to yellow, crack, and peel over time. You need to use a specialist radiator paint or heat-resistant enamel, both of which are widely available and formulated to withstand the temperature fluctuations that radiators go through.
Our heating specialists can help match the right size for your room.
Bronx, NY 10474