Radiant Floor Heat Output
How much heat a radiant floor puts out per square foot, and whether the surface stays comfortable.
Example
You enter
- Solve for surface_to_q
- Floor mean surface temperature (°F) 85
- Room air temperature (°F) 70
You get
- Heat output 29.1 Btu/hr-ft^2
Checked against published worked examples from: ASHRAE Hampton Roads chapter (G. Hayden, P.E.).
Details, formula, and sources
Scopeq = 1.481 x (T_surface - T_room)^1.1 Btu/hr-ft^2 (EN 1264), with the ~85 F surface comfort cap (~29 Btu/hr-ft^2 in a 70 F room). An 85 F floor over a 70 F room gives 29.1; solving inverse, a 30 Btu/hr-ft^2 load needs an 85.4 F surface, just over the cap. Solves either direction. The panel manufacturer's ratings and the loop layout govern.
Formula or tableq = 1.481 x (T_surface - T_room)^1.1 Btu/hr-ft^2 (EN 1264 basic characteristic, 8.92 W/m^2 per K^1.1, converted); inverse T_surface = T_room + (q/1.481)^(1/1.1); comfort cap ~85 F surface.
Source and editionEN 1264 basic characteristic curve for heated floors, q = 8.92 (theta_F - theta_i)^1.1 W/m^2, by name, with the ~85 F surface comfort limit.
Free accessThe floor heat-output correlation and the ~85 F comfort limit are standard published radiant-heating results.
What governsEstimate. AHJ and licensed professional govern.
API field namesmode, t_surface_f, t_room_f, q_btuh_ft2
- Output q = 1.481 x (T_surface - T_room)^1.1 Btu/hr-ft^2 (8.92 W/m^2 per K^1.1)EN 1264
- Comfort cap mean surface temperature limited to ~85 F (~29 Btu/hr-ft^2 in a 70 F room)ASHRAE comfort
- Tubing separate the surface temperature follows from water temp, spacing, and coveringscope of this tile