This article collects the questions that come up once you have drawn your first layout in the radiant floor heating module: why something is not visible, what a warning means, how to fix something. If you are just starting, go through the step-by-step guide first: how to design radiant floor heating in HeatAlgo. The EN 1264 calculation model is explained in the guides on tubing spacing and loop length and on water temperature.
Still gathering information? Start with the quote checklist. Already have a design or a quote? Read the radiant floor heating design guide.
Units on a US account
An account created from the US sees the module in imperial units: feet and inches, ft², °F, Btu/h, and gpm for loop flows. You switch between metric and imperial in Settings ("Units") or in the module's menu. Only what you see and type changes - the calculation stays metric, to EN 1264 and EN 12831-1.
Some values stay metric on purpose: tubing sizes ("16×2 mm"), and the spacing and wall distance, which work in 5 mm steps and show inches first with the millimeters kept (5.9" / 150 mm). The PDF report and the printable plan print in metric units for now.
Rooms and sections
The room is not calculated. A section drawn on the plan must be assigned to a room. Click it, and pick the room in the "Room" field of the section panel. The list in the side panel shows rooms only. A section with no room has its own "Unassigned sections" message in the notice strip above the list, and its "Assign" link opens that section. Rooms come from the heat loss calculation (the import button in the panel brings each room's heat loss and temperature; the label comes from the room's name there, for example "1/12"), or you add them by hand with "Add": a name, the story, the heat loss in Btu/h ("Heat demand"), the room type and the temperature. The type sets the highest floor surface temperature: standard up to 84 °F or bathroom up to 91 °F.
The room balance. The room list shows, for each room, the floor output at the current parameters (for example 95 °F/86 °F supply and return) against the room's heat loss: the surplus in green or the shortfall in orange. Hovering over a row highlights the room on the plan. Clicking opens the room's screen: the figures ("Area", "Floor output", "Demand"), then "Loops", and last "Settings" with the "Name" and "Number" fields. "Demand" is the room's design heat loss, from the heat loss calculation or typed in, and the floor is sized on that whole heat loss (EN 1264-3, Formula (5)). Heat lost downward through the floor is not subtracted from it - it enters only the loops' flow.
The notice strip. Above the room list is one strip; the "‹ 1/3 ›" arrows step through the notices. Pressing a notice shows the full sentence, an explanation and its fix, and its link takes you to what it is about.
The free room. On a free account the first room in which you draw a loop is fully calculated - a message above the list names it. The room counts only once its section is assigned. On the free plan we calculate a few projects at a time, so the first room in a new project may be calculated with a delay, with a date on screen; an unlocked project is calculated in full right away.
A room on the wrong story. In the room's edit view pick "Move to storey". Rooms with drawn loops are tied to their story's plan and cannot be moved while the loops exist. An update from the heat loss calculation ("Update data from the heat loss calculation?") moves only rooms without loops.
Loops, lengths and splitting
A loop too long. The length comes from the real geometry, together with the run to the manifold. The limits depend on the PEX tubing:
| Tubing | Warning from | Hard limit |
|---|---|---|
| 16×2 mm | 262 ft (80 m) | 295 ft (90 m) |
| 17×2 mm | 295 ft (90 m) | 328 ft (100 m) |
The table shows the loop length limits the app applies, run to the manifold included.
A loop with issues has a tinted header with fix links for the spacing and for "Split"; the section panel also shows "Consider splitting this section". With the automatic "Split" you do not pick a direction: the app chooses the cut lines itself and may divide the section into several areas. The arrow beside it opens "Choose the split" with a grid and the expected lengths. When the automatic split fails, the app tells you to choose the split from the arrow. Beside the story tabs, at the top left of the canvas, a long-loops recommendation ("Split N long loops") finds cuts for the whole story at once and shows how many sections can be split. Each part after the split has its own run - the split divides the tubing in the room, not the way to the manifold.
Tubing layout. By default "Auto" chooses between a spiral, a classic meander and a bifilar meander and says why ("Bifilar meander covers a narrow room better", for example). You change the layout in the "Pipe layout" field of the section panel, and the tubing direction, horizontal or vertical. When a shape has no ready layout, the app says "This section shape is best split into smaller areas" instead of drawing a faulty one.
Editing node by node. "Edit nodes" in the section panel copies the generated layout as a manual drawing with editable nodes; from then on, parameter changes do not redraw it. "Restore auto" discards the manual changes and generates the layout again. The "Draw pipes manually" tool (O) draws tubing from scratch inside a section; the list of such sections is in the tool panel under "Hand-drawn pipes".
Holes in a section. Right-click the section and pick "Cut an opening" (for a column or stairs, for example) - the loop avoids the cut-out area. The same menu has "Duplicate section".
Flow, spacing and parameters
Flow below 0.13 gpm (0.5 l/min). The supply water is clearly hotter than the loop needs. Lower the supply temperature to the required one (the project parameters show "Required supply" - the temperature the drawn floors ask for, set by the leading loop outside bathrooms), widen the spacing, or merge a very small section with its neighbor. Flow above 0.4 gpm (1.5 l/min) - split the section.
Spacing wider than recommended. The spacing warning means that, at the project parameters, the room's heat loss needs tubing closer together. The loop's issues and the room's screen have a link that sets the recommended spacing. For the whole story, an "Apply the recommended spacing" recommendation appears beside the story tabs - with a preview of whether any loop would exceed the recommended length because of it. Two recommendations at once fold behind one "2 recommendations" button. The recommended spacing is the widest of 7.9", 6.9", 5.9", 4.9" and 3.9" (200, 175, 150, 125 and 100 mm) on center at which the floor covers the heat loss; the action only tightens the tubing and leaves hand-drawn loops alone. When the heat loss exceeds the floor's output even at 3.9" / 100 mm, the app says so plainly: check the supply temperature and the floor covering, or add a radiator.
Your own spacing. The spacing field in the section panel, and in the panel for several selected sections, offers 3.9" / 100 mm, 5.9" / 150 mm, 7.9" / 200 mm, 9.8" / 250 mm and 11.8" / 300 mm, and "Other...", where you type a value from 50 to 300 mm in 5 mm steps. Any other value is refused with "Enter a multiple of 5." This applies to the radiant floor heating module; the heat pump module and the public loop calculator keep five fixed values.
Edge zone. The "Edge zone" field in the section panel tightens the spacing in a band 1' 8" (0.5 m) wide along the walls. It works only for generated layouts - a manual drawing stays without the tighter band.
Project parameters. The "Project parameters" dialog (from the "..." menu on the toolbar) has three parts: "Temperatures", "Floor" and "Pipe layout". It sets the supply and return temperatures (a new project: 95 °F/86 °F, that is 35/30 °C), the tubing, the default floor covering, the slab over the tubing ("Screed over the pipe", typically 1.8 in (45 mm)), the spacing of the supply and return pair on the runs and the "Pipe distance from wall", and shows the design spread and the required supply. The parameters belong to the whole project, not to one story. The floor output is calculated on the EN 1264-2 thermal characteristic from the tubing actually laid in the section, and the flow to EN 1264-3: G = 0.86 · (Q + Φ_FB) · (1 + Ro/Ru) / σ, in the standard's metric units, where Q is the loop's output to the room and Φ_FB its share of the loss through the floor, split between the room's loops by area.
Distance from the wall. How far the outermost tubing run sits from the edge of the section: 3.9" / 100 mm by default; 2.0" / 50 mm, 3.1" / 80 mm, 5.9" / 150 mm and 7.9" / 200 mm to choose from, or "Other..." from 30 to 500 mm. A change in the project parameters re-lays the existing sections. A section can have its own distance - the first option in its settings, "Project default", goes back to the project's value. A hand-drawn loop has no such field. Below 3.1" / 80 mm a meander turns on its 80 mm bend radius, so the row ends may sit further from the wall.
Return temperature not above the room temperature. The floor then gives off no heat - raise the return temperature in the project parameters. The supply must be hotter than the return, otherwise the flow is not calculated.
Manifolds and runs
You place the manifold with the "Manifold" tool (M), with two clicks at the ends of the cabinet. In its panel you set the number of ports; the warning "More circuits connected than ports" means you need more ports or a second manifold. The "Flow meters" link at the foot of the side panel opens a window with the story's totals at the top (area, tubing, total flow and flow per unit of floor area) and the loops grouped by room, with a subtotal for each room. Each loop has its port, the heat the water carries (EN 1264-3, Formula (13)), the temperature spread and the flow, so on every row the flow is that heat divided by the spread. What flow to set on the flow meters goes deeper.
You draw a run (route) with the "Draw supply route" tool (R) from a section or a manifold; Enter finishes the route at the last point, Backspace removes the last point, Esc cancels. You set the spacing of the supply and return pair on the runs as a default in the parameters, and for one route in its panel; select several routes and right-click to change the spacing of all of them at once.
A route that does not connect to the loop. The loop's issues say what to change. "The pipes cannot join the loop at this point on the wall. Move the end of the route along the section wall." - moving the route is enough. When the issue says the selected pipe layout cannot be bent in this section at that spacing, the problem is in the section itself, not in the route: choose "Auto" or another layout, change the spacing or split the section.
Stories
Stories are tabs above the drawing. "Add storey" offers "Storey above" or "Basement (below)"; you rename a story by clicking its tab, and "Delete storey" removes its background, rooms, loops and manifolds with no undo. Stories imported from the heat loss calculation are created automatically. On a free account you draw on one story - instead of the add menu you see "One floor on a free account", which leads to unlocking the project; stories from the heat loss calculation do not count toward that limit.
Background plan and calibration
Formats and size. PDF, PNG, JPG, HEIC, DWG or DXF; for a multi-page PDF you pick the page in the "Select page" dialog. The plan file can be up to 25 MB. An iPhone photo (HEIC) is converted to JPG, turned upright and stripped of its metadata, location included.
Changing and rotating the background. "Background settings" (an icon on the toolbar) let you change the scan, rotate it by any angle or reset the project. Rotate before you draw - drawn sections, manifolds and routes do not rotate with the background. Rotating and cropping keep the scale. "Replace background" (confirmed in the "Replace the background?" dialog) clears it: "The new plan has its own scale - set it again with the ruler tool. Until then, areas and pipe lengths are not calculated."
Calibration. The "Calibrate" tool (C): two points a known distance apart, and the distance - in feet in the "Distance (ft)" box on an imperial account (16' 5" or 16.4), in centimeters in "Distance (cm)" on a metric one. To set the scale again, open "Project parameters" and click "Change" beside the plan scale. Calibration is per story - every new story needs its own.
Snapping. When the file holds drawing geometry, drawing snaps to the walls. You toggle the grid with G and set its reference point with Alt and a click; Shift forces a 90° angle, Shift with Alt 45°, and Ctrl (Cmd on a Mac) draws without snapping.
Export and more
The printable plan and the full PDF are described in the article on PDF reports, with the messages about the plan preview before export. "Report notes" (the notes icon) go at the end of the PDF. The "Materials" link beside "Flow meters" opens the bill of materials for the supply house.
Keyboard shortcuts and gestures are in the "?" dialog on the module bar; the full list is in the "Handy keyboard shortcuts" section of the guide. The most important: V select, H move a section or manifold, P section, M manifold, R route, O tubing by hand, Space with dragging pans the view, Ctrl with scrolling zooms, Ctrl+Z undoes.
"Project was changed on another device" - someone (or you in another tab) saved a newer version; click "Load newer version". If the floor plan of a story fails to save, the rest of the project is saved; upload the background again with "Upload again".
A new generation of drawings - older projects get an offer to update their layouts and lengths to the new generator. Before updating, download the existing PDF with the button in that dialog, because the layouts and lengths will be recalculated; "Later" postpones the decision.
Drawing needs a computer or a tablet. On a phone the module shows the project's documents: download the report and the bill of materials one by one or together as a ZIP (on a free account, only the report preview); the print plan is set up and downloaded on a computer.
AI sections on your floor plan
You do not have to trace the sections by hand: once the plan is uploaded and the scale calibrated, Algo AI proposes them together with the tubing layout, and you review the proposal on the drawing and apply it. One generation per account is free - the first read of a plan spends it, not Apply. Everything stays editable, and the manifold and the supply runs are yours to draw as before. The whole path is in drawing radiant floor heating sections with AI.
Algo AI names the rooms in the draft from the text on the plan, and gives rooms with no text a name in the app's language. While the draft is open, the drawing is locked: "Apply or discard the draft to edit the drawing." Panning and zooming still work. A request still waiting for a plan or a scale can be canceled free of charge ("Cancel the request?"), and after you discard a draft you can ask for a new one with "Draw again". Algo AI does not place the manifold or draw the supply routes - you do.
A HeatAlgo report follows EN 12831-1 and EN 1264, not ACCA Manual J, and is not accepted for permits or rebates.