Underfloor Heating Pipe Length
Calculator
Results
- Pipe laid in the floor (m)
- 166.666666
- Total pipe length (m)
- 176.666666
- Number of 100 m coils
- 1.766666
HVAC and plumbing results
| Pipe laid in the floor (m) | 166.666666 |
| Total pipe length (m) | 176.666666 |
| Number of 100 m coils | 1.766666 |
formula-map diagram
- Pipe laid in the floor (m)
- 166.666666
- Total pipe length (m)
- 176.666666
- Number of 100 m coils
- 1.766666
HVAC and plumbing relationship
Formula
L = A ÷ spacing + 2 × manifold run= 166.66666666667
Note
This is a simplified model: it applies a standard engineering formula to the numbers you entered. Conversions between BTU/h and kW use the exact factor 1 kW = 3412.142 BTU/h, but every sizing figure is an estimate. Air conditioner sizing uses the common 20 BTU/h per square foot rule of thumb, not a room-by-room load calculation, and it ignores insulation, glazing, orientation, ceiling height, infiltration and local climate. Heating loads use a single volumetric heat-loss factor in W/m³·K rather than a fabric-by-fabric U-value calculation. Air properties are fixed at 1.2 kg/m³ and water at 1000 kg/m³ and 4186 J/kg·K, with no correction for temperature, altitude or glycol. Duct and pipe results use the ideal continuity equation and ignore fittings, bends, roughness and system effect unless you enter those losses yourself. The Hazen-Williams equation is valid only for water in full turbulent flow at ordinary temperatures. Water hammer uses the Joukowsky surge, an upper bound for instant closure. Tank drainage assumes a prismatic tank and steady free discharge. Hot water recovery and condensate figures ignore standing losses and coil bypass. Size real systems with a proper heat-loss survey and have the work checked by a qualified HVAC or plumbing professional.
More in HVAC and plumbing
See all →Frequently asked questions
How does pipe spacing affect the total length needed?+
Tighter spacing between pipe loops (like 150mm versus 300mm) delivers more even heat and higher output per square meter, but requires roughly double the pipe length to cover the same floor area — spacing is a direct trade-off between material cost and heat output.
Why does the calculator need the room's floor area rather than just its dimensions?+
Total pipe length is essentially the floor area divided by the spacing between loops, since the pipe snakes back and forth to cover the whole surface. Irregular room shapes still resolve to the same formula once you know the usable heated area.
Does the calculated length include the pipe run to and from the manifold?+
No, this typically estimates only the pipe within the heated loop area itself. You should add extra length for the supply and return runs connecting the loop to the manifold, especially for rooms far from the mechanical room.
What happens if I use pipe spacing that's too wide for the room's heat loss?+
Wider spacing reduces the pipe's surface contact with the floor, lowering the maximum heat output achievable — in a room with high heat loss (like one with large windows), overly wide spacing may leave the system unable to keep up on the coldest days.
Is a single loop or multiple loops used for larger rooms?+
Most systems split large rooms into multiple loops because a single loop that's too long creates too much pressure drop for the pump to circulate water effectively — manufacturers typically specify a maximum loop length, often in the 80-120 meter range.