Seeing three pipe spacings on one drawing may worry an owner: is someone saving money at one room's expense? Not necessarily. In a well-designed storey, different pipe layouts can deliver consistent comfort. Rooms differ in windows, external wall area, floor finish and temperature requirements. Problems arise when spacing changes without calculation or neither designer nor installer can explain why.
Spacing is the distance between adjacent pipe centrelines. It is not the gap between outer walls or the room's heating output. Ten-centimetre centres mean a denser layout than twenty-centimetre centres, but final heat transfer depends on every floor layer and the water temperature.
Start with room demand, not the coil
First assess design heat losses. Two rooms of equal area may differ substantially: one borders heated spaces and has a small window, while another sits at a corner with full-height glazing. Both being called bedrooms does not justify automatically giving them the same pipe density.
Then establish the active heated area. Dividing room demand by this area gives the required heat flux per square metre of floor. If required output exceeds what the selected construction and finish can deliver acceptably, pipe density cannot simply be increased indefinitely. Reduce losses or consider another heating surface.
What does closer spacing actually change?
Smaller gaps generally help distribute floor temperature more evenly and may achieve the required output with a different water temperature regime under specific conditions. However, no fixed percentage saving can be promised simply by changing from 20 to 15 cm. That would require comparing the same room, construction and heat-source operation.
The Danfoss technical guide includes pipe spacing among several factors determining floor heat output. Layer thickness and floor covering resistance are others. Selecting spacing is therefore not an isolated supplier's table detached from the rest of the design.
A simple example for one storey
Suppose three areas are designed: a 6 m² perimeter zone beside a large window, an 18 m² living area and an 8 m² internal room. For illustration only, consider respective spacings of 10, 15 and 20 cm. No specific outputs are assigned because the construction table and heat losses are unavailable.
| Zone considered | Area | Illustrative spacing | Approximate pipe within the floor |
|---|---|---|---|
| Beside the window | 6 m² | 10 cm | 60 m |
| Living area | 18 m² | 15 cm | 120 m |
| Internal room | 8 m² | 20 cm | 40 m |
Geometry reveals an important consequence: closer spacing increases pipe quantity. Each circuit's connecting runs are also added to the total. Circuit quantity and distribution must be calculated, not determined by cutting the coil wherever it runs out.
A perimeter zone is not necessarily a separate circuit
A denser zone may form part of the same circuit if justified by the design. Elsewhere a separate circuit may suit better. The choice depends on geometry, flows, controls and floor construction joints. The drawing must clearly define the boundary and the installed system must match it.
Owners should ask how different zones will be controlled. If one loop passes through two independently used rooms, one thermostat cannot regulate them separately. Conversely, several circuits serving one open living room may not need separate user-controlled zones. A pipe loop and a room control zone are not the same term.
The floor finish may change the original solution
Tiles, wood and their underlays have different thermal properties. If you choose a different finish after design, give the designer the exact product and its data sheet. 'Suitable for underfloor heating' alone does not establish the entire assembly's resistance or permitted surface temperature.
For example, official Kährs guidance sets specific operating conditions for timber floors. These do not justify applying that manufacturer's limits to every floor covering on the market. They do demonstrate why pipe density alone is insufficient and why choosing a floor finish must be coordinated with the heating design.
It is easier to stop a mistake before screeding
Can spacing change after laying starts?
Sometimes an installer finds the planned pattern does not fit because of actual room dimensions or a relocated service connection. That is a valid reason to pause and agree a revision, not quietly increase spacing throughout the room. Density affects pipe quantity, circuit length and intended heat output. Check changes in both respects: will output remain sufficient, and will the remaining circuits still meet the hydraulic design?
For example, if a denser window zone disappears because pipe ran short during installation, adjusting the pump will not restore the original geometry. While pipes remain visible, corrections are clear and can be documented. After screeding, only indirect adjustment methods remain, and these do not always resolve uneven surface temperatures. Material shortages must therefore be addressed through supply or design, not an unexplained on-site interpretation of the drawing.
Before covering the pipes, compare photographs with the plan. Check that the denser zone remains where specified, walls have not moved during installation and manifold outlets are labelled. If a kitchen or partition moves, the old pipe drawing may not suit the new room geometry.
For acceptance, keep a clear explanation: why this area uses 10 cm, another 15 cm and a third 20 cm; which finish and water temperatures were used in calculations; and the circuit flows. If the only answer is 'it is more economical', ask for specifics. Economy must be assessed alongside comfort and system operating conditions.
If work is only being planned, start with the heat demand calculation and the general underfloor heating guide. Include the plan, window dimensions and proposed finish in your enquiry. The three spacings on the drawing will then become an explainable design choice rather than a guess based on room names.
Information sources
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