Plumbing & Heating
In-Floor Heating Tubing Calculator
Calculates the length of PEX tubing for an in-floor heating loop from area and spacing
Updated June 26, 2026 · Live
What this tool does
Calculates the length of PEX tubing needed for a hydronic in-floor heating system from the heated floor area and the tube spacing, with an allowance for bends and the manifold run.
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How the in-floor heating tubing calculator works
This calculator divides the heated floor area by the tube spacing to get the length of PEX laid back and forth across the room, then adds 10% for the return bends and the leader run to the manifold. Tighter spacing puts more tube in the floor and raises output.
Choosing a tube spacing
Common spacings are 150–200 mm for bathrooms, entryways and rooms with high heat loss, and 300 mm for living areas over a warm basement. Closer spacing gives a more even floor temperature and more output, at the cost of more tube and tighter bends.
Loop lengths and the manifold
Keep individual loops within the manufacturer’s limit — roughly 120 m for 3/8" PEX and 180 m for 1/2" — so the circulator can push flow through without excessive pressure drop. Large rooms are split into several loops that all return to a manifold; size the manifold for the loop count.
What this tool does not do
It estimates tubing length only. It does not perform a room-by-room heat-loss calculation, size the boiler or circulator, or design the manifold and controls — those are the work of a hydronic designer or mechanical contractor.
Adjusting the defaults
Every input is editable. Enter your own heated area, spacing and price and the tubing length and cost recalculate instantly. Run it once per room or zone and add the loops together for the whole job.
On-site considerations
Pressure-test every loop with air or water before the pour and keep it under pressure while the concrete or gypcrete goes down, so a nicked tube shows up before it is buried. Staple or clip the PEX to the spacing you planned — drift widens cold stripes in the floor. Insulate under the slab so the heat goes up, not into the ground.
Using this alongside other BuildMetricLab tools
Pair this with the room volume, floor screed and concrete slab calculators when planning a heated floor, and with the material cost calculator to price the tube, manifold and fittings. Every BuildMetricLab tool runs in your browser — no sign-up, no data sent anywhere, and every formula is shown so you can audit the math.
Sources & methodology
Calculates the tubing run as the heated floor area divided by the tube spacing, plus 10% for bends and the leader pipe to the manifold. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are roof strapping / furring strip calculator results accurate enough to order materials?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
What wastage percentage should I use?
The calculator defaults to the typical Canadian trade allowance for roofing. Increase it for complex cuts, awkward shapes, or first-time DIY. The default wastage allowance reflects common trade practice; values lower than the default may underestimate offcuts.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, the National Building Code (NBC), property-line or shared-wall, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the unit prices?
Yes — every price field is editable. Plug in your supplier's quote to get a total that matches your project.
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