Short answer: a useful radiant floor heating design connects three things: what each room needs, how the proposed floor will provide it, and where the tubing goes. If you only have a drawing of loops, you cannot yet tell whether it works. Ask for the room loads and the loop schedule, then check that they agree, room by room.
Forums are full of people asking for exactly this check. A homeowner on HeatingHelp asked for a "sanity check of new radiant heat design" drawn in LoopCAD; others post a layout from the tubing supplier or their own sketch. Whatever drew the layout, the checks below are the same.
This guide covers hydronic radiant floor heating with tubing in a slab or thin slab. If you are still gathering floor plans and product details, start with the radiant floor heating quote checklist.
Start with the drawing's version and scope
Check that the drawing shows the room layout you actually plan. An old kitchen plan can make a neat-looking layout useless once an island, doorway or wall moves.
Look for the project name, floor, revision or issue date, room labels and a scale. Ask which dimensions were measured and which came from the original drawing, and note anything that may still change. Discuss fixed cabinets, bathroom fixtures and other obstacles with the contractor rather than assuming one exclusion rule fits every system.
First questions:
- Is this the latest floor plan?
- Which rooms and areas does the layout cover?
- Which measurements or decisions are still waiting for confirmation?
- Who updates the layout if they change?
Check the room loads and how the floor output was worked out
Ask for the heat requirement of each room and the assumptions behind it. For a US house that is the contractor's room-by-room load calculation. Then ask how the floor output was checked against each room's requirement. Floor area alone does not explain either number.
For tubing embedded in concrete, EN 1264-2 gives the floor's output from the tubing spacing, the floor covering's thermal resistance, the depth of concrete over the tubing and the tubing size, together with the difference between the water and the room temperature. A limit on the floor surface temperature caps it. That is why switching from one floor covering to another is a reason to revisit the design, even when both are sold as suitable for radiant heat.
Joist-space, staple-up, plate and panel systems use other calculation models or the manufacturer's tested outputs. HeatAlgo does not calculate them; if that is your system, ask its manufacturer for the output data.
You do not need to choose a spacing or a water temperature yourself. Ask where the chosen values are documented and who confirms them for your system. The guide to radiant floor heating water temperature explains how temperature, covering and output relate.
Match the loops on the drawing to the schedule
A loop label connects a line on the drawing with a row in the schedule. Ask the designer to walk you through one loop from start to finish, including its runs to and from the manifold.
Find the tubing specification, spacing, length and calculated flow for each loop; loop flow and the supply-to-return temperature drop follow EN 1264-3. If a room has several loops, check the drawing and schedule name them the same way. Ask what each length includes: a room-only length and a full loop length are different numbers. The guide to tubing spacing and loop length explains why the runs outside the room matter. Loop-length limits come from your tubing manufacturer, not from an online example.
Example: reading a loop schedule
Below is the schedule from a HeatAlgo report for Cedar House, a fictional demonstration project calculated in metric units. The US figures are converted from the report; the metric originals are in brackets. They show what the fields mean, not settings for another house.
Room rows (demonstration report UFH-CEDAR-DEMO, 20 September 2026)
| Room | Floor output | Heat loss | Balance |
|---|---|---|---|
| Kitchen | 2,549 Btu/h (747 W) | 2,218 Btu/h (650 W) | 331 Btu/h (97 W) |
| Living / Dining | 6,398 Btu/h (1,875 W) | 6,350 Btu/h (1,861 W) | 48 Btu/h (14 W) |
| Bedroom | 2,774 Btu/h (813 W) | 2,368 Btu/h (694 W) | 406 Btu/h (119 W) |
| Total | 11,720 Btu/h (3,435 W) | 10,935 Btu/h (3,205 W) | 785 Btu/h (230 W) |
The heat loss belongs to the room, and the balance compares the floor output with it. HeatAlgo sizes the floor on the room's whole heat loss, as EN 1264-3 requires. When rooms are linked to a heat loss calculation, the heat lost downward through the floor is not subtracted from the requirement; it is added to the water flow in the loops instead, which keeps the flow on the safe side. Cedar House's heat losses were entered directly, so that rule does not change the table.
Loop rows (the same report)
| Loop | Spacing | Tubing length | Flow | Floor output |
|---|---|---|---|---|
| 0/3/A (kitchen) | 3.9 in (100 mm) | 176.5 ft (53.8 m) | 0.18 gpm (0.7 l/min) | 1,447 Btu/h (424 W) |
| 0/3/B (kitchen) | 7.9 in (200 mm) | 98.4 ft (30.0 m) | 0.16 gpm (0.6 l/min) | 1,102 Btu/h (323 W) |
| 0/1/A (living) | 7.9 in (200 mm) | 161.1 ft (49.1 m) | 0.37 gpm (1.4 l/min) | 1,481 Btu/h (434 W) |
| 0/1/B (living) | 7.9 in (200 mm) | 139.4 ft (42.5 m) | 0.37 gpm (1.4 l/min) | 1,433 Btu/h (420 W) |
| 0/1/C (living) | 7.9 in (200 mm) | 184.1 ft (56.1 m) | 0.45 gpm (1.7 l/min) | 1,767 Btu/h (518 W) |
| 0/1/D (living) | 7.9 in (200 mm) | 166.3 ft (50.7 m) | 0.42 gpm (1.6 l/min) | 1,716 Btu/h (503 W) |
| 0/4/A (bedroom) | 5.9 in (150 mm) | 163.1 ft (49.7 m) | 0.18 gpm (0.7 l/min) | 1,389 Btu/h (407 W) |
| 0/4/B (bedroom) | 5.9 in (150 mm) | 167.3 ft (51.0 m) | 0.18 gpm (0.7 l/min) | 1,385 Btu/h (406 W) |
| Total | - | 1,255.9 ft (382.8 m) | 2.30 gpm (8.7 l/min) | 11,720 Btu/h (3,435 W) |
Loop outputs add up to the room output. The kitchen shows it: 1,447 Btu/h from loop 0/3/A and 1,102 Btu/h from loop 0/3/B make 2,549 Btu/h against a 2,218 Btu/h requirement, a 331 Btu/h balance. The requirement is shared between the loops, not repeated: the report gives loop 0/3/A 1,259 Btu/h (369 W) and loop 0/3/B 959 Btu/h (281 W), in proportion to their output. These are calculated values in a demonstration report, not measurements from an installed system.
You can check any flow by hand. The report works out each loop's flow to EN 1264-3 from the heat the water carries and the temperature drop across the loop; in US units that is the familiar gpm = Btu/h ÷ (500 × temperature drop in °F). Tubing length is the whole loop: the tubing in the room plus the supply and return runs to the manifold.
One length changed after this report was produced. Since 24 September 2026 the app lays out loop 0/3/B so that every bend has the radius it needs, and that loop comes out 5.6 ft (1.7 m) longer: 104.0 ft (31.7 m) instead of 98.4 ft. The floor then takes 1,261.5 ft (384.5 m) of tubing instead of 1,255.9 ft. The table copies the 20 September report unchanged.
One input here was more favorable than the standard's design procedure. When the report was produced, HeatAlgo evaluated each covering at its own thermal resistance: tile 0.05, vinyl 0.08, wood 0.12 and carpet 0.15 m²K/W (SI units; US product sheets give R-value in ft²·°F·h/Btu). Cedar House is tiled. EN 1264-3 designs a home's floors for a covering of at least 0.10 m²K/W, and HeatAlgo now does the same, so tile and vinyl are calculated at 0.10. Recalculated that way, the same floor falls short in all three rooms at a 102.2 °F (39 °C) supply water temperature and needs about 109.4 °F (43 °C). Ask which covering resistance your own design assumed.
In the app, living-room loops 0/1/C and 0/1/D each carry an advisory: their flow is above HeatAlgo's 0.40 gpm (1.5 l/min) threshold, and the app suggests splitting each in two. The demonstration left both open. The PDF does not list advisories, so ask whoever prepared a layout whether any were left open, and why.
Each row suggests a question. On spacing: which inputs led to it? On length: which runs are included? On flow: who sets and checks it at startup? On output: how does this loop add to the room's total?
Check the manifold and controls
Find the manifold on the drawing and follow the runs to it. Ask how it will be reached once cabinets and finishes are in. If two locations are on the table, have the runs checked for both before deciding; see where to put the radiant floor manifold.
Ask which rooms you will control separately and how the supply water temperature is set: a mixing valve, outdoor reset, or both. A loop drawing alone does not cover the wiring or the connection to the boiler or heat pump. Note who is responsible for each open item, especially when the heating, the slab and the flooring come from different companies.
Compare what the bids include
Use the same items for each bid and write included, excluded or to confirm, with the document and the person confirming it. A blank is a question, not proof something was left out.
| Item to clarify | Bid A | Bid B | Document and person |
|---|---|---|---|
| Current floor plan and revisions | |||
| Room loads and stated inputs | |||
| Loop layout, labels and schedule | |||
| Insulation under and at the edges of the slab, concrete or thin slab | |||
| Manifold, runs and access | |||
| Supply water temperature, mixing or outdoor reset, controls | |||
| Pressure test before the slab is poured, loop flow settings, startup | |||
| Slab warm-up, then flooring and restoration | |||
| Final documents, operating guidance and warranties | |||
| Design changes, responsibility and extra charges |
If Bid A says "loop layout supplied" and Bid B says "layout and room loads supplied", those are different pieces of work. Ask Bid A where the room loads are documented. EN 1264-4 provides for a pressure test before the slab is poured; ask which manufacturer instructions apply to testing, startup and the initial warm-up.
What you can prepare in HeatAlgo
HeatAlgo's radiant floor heating software lets you prepare a hydronic layout and its calculations from your inputs, for tubing in a slab or thin slab. For joist-space, staple-up or plate systems, use the system manufacturer's output data instead.
You enter each room's load, check the inputs and the layout, then can buy the printable plan and PDF report to discuss with your contractor, and the bill of materials. The account is free and needs no card. Before you buy, the preview shows the building summary and one fully calculated room; the paid report unlocks the remaining rooms and the full loop details for that project. The report does not include a site visit, installation or sign-off; agree those separately for your house and system.
The engine behind these figures also calculated HeatAlgo's reference house, a 102.2 m² (1,100 ft²) house calculated for a Warsaw design day of -20 °C (-4 °F), with every input published for checking.
Start a free radiant floor layoutA HeatAlgo report follows EN 12831-1 and EN 1264, not ACCA Manual J, and is not accepted for permits or rebates.