There is no single right place for an underfloor heating manifold. You choose it by weighing three things together: the runs from the manifold to each room, the loop-length limit of your pipe system, and access to the cabinet. A central position shortens the runs, but that is only one of the three.
To see how much the position changes, we put the manifold in two places on one demonstration floor and let HeatAlgo calculate both, with every other input the same. Below are the results, what they do not show, and a worksheet for comparing two positions in your own home. If you are still collecting plans and product details, start with the underfloor heating planning checklist.
What the manifold position decides
- The runs to each room. Every loop has its own pair of pipes to the manifold, a flow and a return, so each metre between the manifold and a room adds about two metres of pipe to that loop. The pipe-spacing and loop-length guide explains why the run counts towards the loop's length.
- Whether the longest loop stays within your system's limit. Each pipe system has a maximum loop length, run included. A loop that would exceed it has to be split in two, and the second loop needs its own outlets on the manifold.
- The pipes that pass through halls and doorways on the way, and the heat they give off there.
- The cabinet itself: a wall that can carry it, room below the manifold for the pipes to bend up, and access for servicing once the house is furnished.
One floor, two manifold positions
We used the fictional Cedar House ground floor from our guide to what an underfloor heating design should include: a 10 × 8 m single-storey plan with a living and dining room, a kitchen, a bedroom and a hall between them, heated by eight loops. In position A the manifold stands at the end of the hall, where that guide's demonstration report has it. In position B it stands on the hall wall halfway along, opposite the living-room door.
Everything else stayed the same: the rooms and their heat loads, the eight loops and their pipe spacings, 16×2 mm pipe under 45 mm of screed, ceramic tiles, and a design flow and return of 43/38 °C. Each pipe pair also leaves its room at the same point in both positions, so the loops inside the rooms are identical and every difference below comes from the runs through the hall.
Position A is where the demonstration put the manifold, with its runs as they were drawn then. Position B is ours: we placed the cabinet so its outlets line up with the living-room runs, and drew the eight new runs so that none cross. In both positions the pipes leave every room through its doorway; where pipes can pass through a partition next to the manifold, both positions would give different runs.
The design guide's report used 39/34 °C. HeatAlgo now evaluates tiles at 0.10 m²K/W, the covering resistance EN 1264-3 takes for dwellings, and at that value this floor needs a flow temperature of 42.2 °C, which the report rounds up to 43 °C. Both runs therefore use 43/38 °C, and every room is covered in both.
The same floor, two manifold positions
A: at the end of the hall
Runs: 86.8 m · longest loop: 0/1/C (Living / dining), 56.1 m
Out of the way at the end of the hall. The pipes of all eight loops run side by side along the hall from the living-room door to the cabinet.
B: halfway along the hall
Runs: 51.6 m · longest loop: 0/3/A (Kitchen), 54.8 m
On a side wall opposite the living-room door, in a 1.4 m wide hall. The pipes arrive from three directions, in short bundles.
- Flow pipe of a run
- Return pipe of a run
- Loop in the room, the same in A and B
- Manifold
What HeatAlgo calculated
| Result | A: end of the hall | B: halfway along the hall |
|---|---|---|
| Runs of all loops (flow and return pipe) | 86.8 m | 51.6 m |
| Pipe inside the heated sections | 296.1 m | 296.1 m |
| Pipe in total | 382.8 m | 347.6 m |
| Longest loop, run included | 0/1/C, 56.1 m | 0/3/A, 54.8 m |
| Loops above HeatAlgo's 80 m warning for 16×2 mm pipe | none | none |
| Flow of all loops together | 450.7 l/h | 450.7 l/h |
| Warnings in the app | none | none |
| Loop | Run A [m] | Loop A [m] | Run B [m] | Loop B [m] |
|---|---|---|---|---|
| 0/3/A (kitchen) | 3.9 | 53.8 | 4.9 | 54.8 |
| 0/3/B (kitchen) | 5.1 | 30.0 | 3.2 | 28.1 |
| 0/1/A (living) | 15.3 | 49.1 | 10.7 | 44.5 |
| 0/1/B (living) | 9.7 | 42.5 | 5.6 | 38.5 |
| 0/1/C (living) | 16.0 | 56.1 | 10.8 | 50.9 |
| 0/1/D (living) | 11.5 | 50.7 | 5.7 | 44.9 |
| 0/4/A (bedroom) | 12.0 | 49.7 | 4.3 | 42.1 |
| 0/4/B (bedroom) | 13.3 | 51.0 | 6.2 | 43.9 |
| Total | 86.8 | 382.8 | 51.6 | 347.6 |
Moving the manifold halfway along the hall cut the runs from 86.8 to 51.6 m of pipe, 35.2 m less, and the pipe in total by about 9%. Seven of the eight loops got shorter, by 1.9 to 7.7 m. One got longer: kitchen loop 0/3/A, by 1.0 m, because its pipes leave the kitchen above position B on the plan and now run down the hall instead of up it. The longest loop, the one that counts against the limit, changed least: 56.1 m at A and 54.8 m at B, 1.3 m shorter, and at B it is a different loop. No loop came near the 80 m from which HeatAlgo warns about a 16×2 mm loop: the longest was 56.1 m at A and 54.8 m at B. Totals and differences are worked out before rounding, so the rounded rows can differ from them by up to 0.2 m.
The flows did not change. HeatAlgo sets each loop's flow from its share of the room's heat load and the temperature drop along the loop, following EN 1264-3, and neither depends on where the manifold hangs. The loop outputs, the room balances and the required flow temperature were the same in both positions too. These are calculated values for a fictional floor, not measurements of an installed system.
What the numbers do not show
- Pressure drop and balancing. Water loses pressure along the pipe, so a longer loop asks more of the pump, and loops of similar length are easier to balance against each other - Wavin's UK guidance links short loops to a balanced system. HeatAlgo does not calculate pressure drop. Ask your installer which loop is the most demanding and how the others will be set on the manifold.
- The heat from the runs. HeatAlgo counts every run in its loop's length, but not the heat it gives off on the way, and the hall in this example has no loop of its own. At A the pipes of all eight loops run side by side up the hall from the living-room door to the cabinet, and the bedroom pipes run most of its length; at B they arrive from three directions and meet at the cabinet halfway along it. Where pipes bunch together, Grant's installation guide advises insulating them so the floor does not overheat, especially if they are not meant to heat the space they pass through. Whether the runs should warm the hall is a design decision, not a by-product.
- The cabinet and its wall. Position B puts the cabinet on a side wall halfway along a 1.4 m wide hall, where a surface-mounted cabinet takes about 14 cm of its width; position A keeps it against the end wall. On this plan position B sits where the kitchen-bedroom wall meets the hall wall, so only a surface-mounted cabinet fits there, and position A is on an outside wall - ask your builder before recessing anything into it. The same guide asks for a wall that is flat, sound and able to carry the manifold, plus the pump and mixing valve where fitted, and for the manifold to stay accessible for maintenance. The partitions on this plan are 12 cm thick, so check the depth of a recessed cabinet against the wall before choosing one.
- Your own house. This is one fictional single-storey floor. Your loops, distances and pipe system give different numbers, and on a plan with long runs a loop can pass its limit where none did here. HeatAlgo calculates floors with the pipe laid in a screed (type A in EN 1264); for a dry system, ask its manufacturer for output data.
Compare two positions on your own plan
Mark both candidates on your plan, then answer the same questions for each. Print the worksheet or copy it into a spreadsheet with the buttons under it; the print dialog also lets you save it as a PDF. A blank answer is a question for your installer, not a no.
| Question | Position A | Position B |
|---|---|---|
| Where exactly the cabinet goes, and on which wall | ||
| Surface-mounted or recessed, and whether the wall can take it | ||
| Room below the manifold for the pipes to bend up into it | ||
| Access for servicing, with doors open and furniture in place | ||
| Route of every loop to the manifold, drawn on the plan | ||
| Longest loop, run included, against the pipe system's limit | ||
| Outlets needed, spares included, against the manifold's size | ||
| Where pipes bunch together, and whether they are sleeved or insulated | ||
| Power and wiring for the actuators and room thermostats | ||
| Pipes to the heat source, filling and venting |
What you can check in HeatAlgo
In HeatAlgo you draw the heated sections on your plan, place the manifold and draw each run from its room to the manifold. The app shows each run's pair length and each loop's length with its run. It flags a 16×2 mm loop longer than 80 m and treats 90 m as its limit; for 17×2 mm the figures are 90 and 100 m. When you move the manifold, the app keeps the path you drew for each run, moves only its end with the manifold and recalculates the lengths. To compare two positions fairly, redraw each run along the way its pipes would really go to the new position, as we did for position B; otherwise the old paths make the new position look longer than it is. It does not calculate pressure drop or the heat the runs give off. For the steps, read how to use the underfloor heating module.
On a free account, with no card required, you can draw the whole floor and see the building summary and one fully calculated room. The paid report unlocks the other rooms' results, including their run and loop lengths, and the printable plan. A report is a basis for the conversation with your installer, not an approved design: it does not include a site visit, installation or sign-off.
See how to prepare a layout for your installer