Underfloor heating room by room
Underfloor heating for a 25 m² room
A 5 x 5 m room at 150 mm spacing. Below is the real loop geometry - not a rule of thumb from floor area - computed by the same engine that draws loops in the underfloor heating module.
This page assumes: manifold 8 m from the room, 150 mm spacing, 35/30 °C flow and return, 20 °C room temperature. For your own room, use the calculator.
The result
The answer for this room
- Loops
- 2
- Pipe in total
- 172.1 m
- Of which the run
- 15.6 m
A single loop here would be 172.1 m against a recommended limit of 100 m per circuit, so the engine splits this room into 2. A longer circuit means more pressure drop, and the harder it is to balance against the others on the same manifold.
The loop in a 5 x 5 m room
Spacing
How spacing changes the pipe length
The same 5 x 5 m room at five spacings. The run to the manifold is counted separately.
| Spacing | In the room | Run | Pipe in total | Loops |
|---|---|---|---|---|
| 100 mm | 233.4 m | 15.7 m | 249.1 m | 3 |
| 150 mm | 156.5 m | 15.6 m | 172.1 m | 2 |
| 200 mm | 118.4 m | 15.6 m | 134.0 m | 2 |
| 250 mm | 96.1 m | 15.7 m | 111.8 m | 2 |
| 300 mm | 80.3 m | 15.7 m | 96.0 m | 1 |
The run is the distance from the manifold to the room and back, at 8 m. The table describes ONE circuit - split the room and every loop carries its own run, so the pipe order grows with it.
Why the (area ÷ spacing) × 1.1 formula is wrongOutput
How much heat 25 m² of floor delivers
At 35/30 °C and 150 mm spacing. The covering decides it: the higher its thermal resistance, the less heat reaches the room.
| Covering | Output per m² | Whole room (25 m²) |
|---|---|---|
| Tile | 50.0 W/m² | 1,250 W |
| Vinyl | 44.6 W/m² | 1,115 W |
| Wood | 39.1 W/m² | 978 W |
| Carpet | 35.7 W/m² | 893 W |
This is what the floor delivers at these settings - not the room's heat loss. Whether one covers the other is settled by a heat load calculation for the whole building.
How flow temperature changes these figuresThe set
Other room sizes
The same calculation for the other rooms in this set.
FAQ
Frequently asked questions
How many loops does a 25 m² room need?
At 150 mm spacing with the manifold 8 m from the room, the engine gives 2 loops, because a single circuit would be 172.1 m including the run, against a recommended limit of 100 m. Changing the spacing or the manifold distance changes that number - the table above shows by how much.
How many metres of pipe for a 25 m² room?
156.5 m in the room itself at 150 mm spacing, plus the run to the manifold. The pipe does not run right up to the wall - it is set back by 100 mm - so the result is lower than floor area divided by spacing.
Are these figures computed or estimated?
Computed. The drawing and the lengths come from the same geometry engine that lays out loops in the HeatAlgo underfloor heating module, and the output per m² from the hydraulics engine. The values are committed to the repository and a test compares them against a live engine run, so a change in the engine breaks the test instead of quietly changing this page.
Your room has different dimensions
The calculator takes any rectangle and draws the loop straight away, with no account. For a whole house, room by room, the underfloor heating module does it in the app.