Hydronic Radiator Size Calculator
Estimate room heating load, corrected radiator output, required radiator units and material cost from area, ceiling height and editable design factors.
Default project preview
10,890 BTU/h
Radiator units
3
Corrected output per unit
4,250 BTU/h
Installed output
12,750 BTU/h
Capacity margin
17.1%
Calculator
Build the material order
Your order will appear here
Enter the project details and calculate a rounded material estimate.
Methodology
Transparent calculation
BuildMeter converts every input to a consistent internal unit, applies the selected allowance, and rounds products up to whole purchasable units.
Room load = area × base load rate × ceiling factor × envelope factor × reserve. Corrected radiator output = rated output × water-temperature factor. Units are rounded up.
FAQ
Hydronic Radiator Size Calculator questions
Why does water temperature change radiator output?+
Radiator output falls as the average water-to-room temperature difference becomes smaller.
Can this size pipework and pumps?+
No. Hydronic flow, pipe diameter, pressure loss and balancing require a complete system calculation.
Should every room use the same load rate?+
No. Windows, exterior walls, infiltration, orientation and insulation can make room loads very different.