Reference house
We calculated one house and we are showing all of it
The full input set, every step of the calculation and the result from four modules. Take the numbers and check us.
Where this house came from
We designed it ourselves, and we say so plainly
It is not a client's project. If it were, we could not publish its inputs, and a page without inputs proves nothing.
We designed the house to be ordinary: a single-storey detached home built to something close to today's requirements, with heat recovery ventilation, underfloor heating and a heat pump. We did not shop for geometry that flatters the result.
Inputs
The whole house in one table
Eight rooms, internal dimensions, design temperatures. Nothing is hidden and nothing is rounded in our favour.
| Room | width m | length m | area m² | θint °C | Φ W |
|---|---|---|---|---|---|
| Living room | 7.0 | 4.0 | 28.00 | 20 | 1 339.78 |
| Kitchen | 4.0 | 2.5 | 10.00 | 20 | 380.51 |
| Main bedroom | 4.6 | 3.5 | 16.10 | 20 | 753.33 |
| Bedroom 1 | 3.5 | 3.4 | 11.90 | 20 | 449.51 |
| Bedroom 2 | 3.5 | 3.4 | 11.90 | 20 | 449.51 |
| Bathroom | 3.0 | 2.7 | 8.10 | 24 | 311.31 |
| Hall | 3.4 | 3.0 | 10.20 | 20 | 552.88 |
| Utility room | 2.0 | 3.0 | 6.00 | 16 | 418.49 |
| Total | 102.20 | 4 655.32 |
- Every area is width times length - exactly, not approximately.
- The area column sums to the heated floor area of the house.
- Gross external wall area is the perimeter times the storey height.
- The outdoor design temperature comes from the climate table for the named city, not from an assumption.
Every input in one file - exactly what the ventilation, heat loss and heat pump engines ran on: download the reference house (JSON)
Envelope and airtightness
Transmission cannot be recomputed without these, so here they are in full. One value per element kind, because this house genuinely has one.
- City
- Warszawa
- Outdoor design temperature
- -20 °C
- External wall perimeter
- 40.3 m
- Gross external wall area
- 104.78 m² = 40.3 × 2.6 m
- External walls U
- 0.20 W/(m²·K)
- Roof U
- 0.15 W/(m²·K)
- Floor on ground U
- 0.25 W/(m²·K)
- Windows U
- 0.90 W/(m²·K)
- External doors U
- 1.30 W/(m²·K)
- Window and door area
- 28.44 m²
- Airtightness n50
- 1.5 h⁻¹
- Heat recovery efficiency
- 85%
Eight rooms at one scale
How we calculate it
Four modules, in the order the engines force
That order is not an editorial choice. The heat loss engine refuses a house with heat recovery ventilation until it knows the design airflows, so ventilation genuinely runs first.
Design airflows
Table from PN-83/B-03430 clause 2.1.2; occupancy and air changes are ours
For each room we compute three values and adopt the largest. The first is the flow from the PN-83/B-03430 table; the other two - from occupancy and from an air change rate - are our own design criteria, and we say so rather than implying the standard sets them. The table below names the criterion that decided each room. The heat recovery system is then balanced: extract rises to meet total supply, and it is that balanced figure the heat loss consumes.
Heat loss
EN 12831-1:2017, U values to ISO 6946, ground to ISO 13370
Transmission through the envelope, ventilation with heat recovery, and the thermal bridge supplement per Annex B.2.1. It is those three components that sum to the building's design heat loss - not the sum of the individual room figures, for two reasons. The standard takes the ventilation share once, for the whole zone. And a partition to another heated room of the same dwelling counts in its own room's load (EN 12831-1:2017, § 6.3.1.3, Formula (3)) but not in the building's (§ 6.3.1.2, Formula (2)), because that heat never leaves the dwelling.
Heat pump sizing
Equipment catalogue on an EN 14825/14511 basis
The pump module does not estimate the load a second time - it reads the heat loss result and adds a design margin. The flow temperature follows from what the underfloor system can deliver at the given pipe spacing and floor covering.
Underfloor loops
Spacing and manifold run stated beside the table
For each room we compute the pipe length and check whether one loop stays inside the limit. Where it does not, the engine splits the room into as many loops as it takes - the living room gets three.
Living room, at the spacing stated below
The living room's pipe, as the engine lays it
Result
What the engines returned for this house
- Design heat loss
- 4 382.07 W
- transmission plus ventilation plus thermal bridges
- Per square metre
- 42.88 W/m²
- the load divided by the heated floor area
- Heat pump capacity
- 4.91 kW
- the load with the design margin added
- Flow temperature
- 40 °C
- follows from the underfloor output, not from an assumption
- Design airflow
- 176.54 m³/h
- total supply for the dwelling
- Longest loop
- 88.1 m
- a single run of pipe, not the room's total
What the result is made of
The three components, broken out, because it is these that sum to the building figure - and because without the split you cannot tell whether a low result is low for a good reason.
- Transmission through the envelope
- 3 434.96 W
- Ventilation after heat recovery
- 533.77 W
- Thermal bridges
- 413.34 W
- Building design heat loss
- 4 382.07 W
Thermal bridges use the additive method of EN 12831-1 Annex B.2.1: a ΔU_TB supplement added to every element facing the outside or an unheated space (Formula (6)). A floor on the ground carries none, because Formula (8) has no bridge term. This house's “standard” class gives the value below. ΔU_TB = 0.05 W/(m²·K)
The watt column in the input table adds up to a different number from this one, and it should. A single room's load is computed with its own worst-case infiltration share, because that is what the emitter in that room has to cover. For the building, the standard takes the ventilation share once across the zone, so the directional surcharge cancels. The first number sizes emitters; the second sizes the heat source. Each sits under its own column.
Room by room
The result from the three modules that work room by room - heat loss, ventilation and underfloor. The pump is sized for the whole house, so it has no column here. "Adopted" is the flow the criterion beside it produced; "balanced" is the same flow after supply and extract are evened out across the system, and that is the figure the heat loss consumes. The adopted column, summed over the supply rooms, is exactly the design airflow published above.
| Room | Φ W | adopted m³/h | criterion | balanced m³/h | role | loops | one loop m |
|---|---|---|---|---|---|---|---|
| Living room | 1 339.78 | 72.8 | air changes | 72.8 | supply | 3 | 72.6 |
| Kitchen | 380.51 | 52.0 | air changes | 90.0 | extract | 1 | 74.4 |
| Main bedroom | 753.33 | 41.86 | air changes | 41.86 | supply | 2 | 64.0 |
| Bedroom 1 | 449.51 | 30.94 | air changes | 30.94 | supply | 1 | 88.1 |
| Bedroom 2 | 449.51 | 30.94 | air changes | 30.94 | supply | 1 | 88.1 |
| Bathroom | 311.31 | 50.0 | table | 86.54 | extract | 1 | 64.6 |
| Hall | 552.88 | 26.52 | air changes | 26.52 | transfer | 1 | 78.0 |
| Utility room | 418.49 | 0.0 | table | 0.0 | transfer | 1 | 49.3 |
Pipe spacing: 150 mm · Run to the manifold, one way: 8 m
The engine has a compliance gate of its own and signed this calculation “complete”. Had an input the standard requires been missing, it would have refused to calculate rather than return a number.
We state the scope of that compliance the same way we state it everywhere else: residential buildings with gravity, mechanical or heat recovery ventilation, and no air transfer devices between zones. This house sits inside it, which is why the engine calculated it through to the end.
The pump module scores its own selection separately and returned the status below for this house: the power class covers the demand with the headroom the module recommends. This is a preliminary sizing, not an installation design. recommended (headroom the module recommends: 0.49 kW)
Bill of materials
What to order from the wholesaler for this house's underfloor heating
The same loops, turned into a wholesaler list - the way the app does it. The first table follows from the loops in the table above. The second rests on the assumptions shown in the "Assumed" column, so confirm them before you order.
From the design
| Item | Qty | Unit |
|---|---|---|
| Heating pipe 16×2 mm, λ = 0.35 W/(m·K) (e.g. PE-X, PE-RT), 600 m coilA different pipe changes the calculation | 1 | coil |
| Heating pipe 16×2 mm, λ = 0.35 W/(m·K), 200 m coil | 2 | coil |
| Manifold with flow meters, 11 loops (R1, Ground floor) | 1 | pcs |
| Compression fitting 16×2 (Eurocone), 2 per loop | 22 | pcs |
| 90° bend guide, 16 mm, 2 per loop | 22 | pcs |
| Thermoelectric actuator, 1 per loop | 11 | pcs |
Coil cutting plan
| Coil | Loops | Offcut |
|---|---|---|
| 600 m coil | 0/1/A, 0/1/B, 0/1/C, 0/6, 0/3/A, 0/3/B, 0/8 | 94.8 m |
| 200 m coil | 0/4, 0/5 | 7.8 m |
| 200 m coil | 0/7, 0/2 | 31.9 m |
3 coils · 1 000 m · offcut 134.5 m
865.03 m of pipe in 11 loops, with 1.0 m spare per loop; 200, 600 m coils, packed for the whole job
The pipe to order is, for each loop, the larger of two lengths - drawn, or area ÷ spacing - plus the run to the manifold and the spare, so it can exceed the loop lengths in the table above. The list never orders short.
Loop codes: 0/1 Living room · 0/2 Kitchen · 0/3 Main bedroom · 0/4 Bedroom 1 · 0/5 Bedroom 2 · 0/6 Bathroom · 0/7 Hall · 0/8 Utility room. A letter after a code is the next loop in the same room. Every loop is one piece of pipe, with no joint in the screed.
Confirm before ordering
| Item | Qty | Unit | Assumed |
|---|---|---|---|
| Insulation under the loops, Ground floor | 107.4 | m² | 102.2 m² heated +5%; R ≥ 1.25 m²K/W over the ground or an unheated space (EN 1264-4, Table 1) |
| Edge insulation strip 150 mm | 5 | roll | section perimeter 113.0 m +5%; 25 m roll |
| Grid-printed foil | 119 | m² | insulation area +10% for overlaps |
| Pipe clips (tacker staples) 16 mm | 8 | box | 1 every 0.4 m of pipe (865.03 m), box of 300 |
| Wiring centre | 1 | pcs | 1 per manifold with actuators |
| Room thermostat | 8 | pcs | 1 per room with a loop |
Order the insulation only if it is not already part of the floor build-up in the building design. Insulation and strip are counted under the loops - floor with no heating under it is not included.
Not included: manifold cabinets, pump and mixing group, movement joints and screed - they depend on the system and the building design. Quantities are approximate.
Questions
Before you ask
Can I check these numbers myself?
Yes, and that is what the page is for. Areas, dimensions, design temperatures, thermal transmittances, airtightness and heat recovery efficiency are all published. Every column adds up to the figure beneath it, to the watt. The one number that is deliberately not a column total is the building design heat loss, and we say beside it why.
Why is the result lower than my installer expects?
Because this is a standards calculation, not a rule of thumb per square metre. A house with heat recovery ventilation and a tight envelope has a small ventilation share. All three components - transmission, ventilation, thermal bridges - are broken out separately in the result section, so you can see where the difference comes from.
Does this page prove your engine complies with the standard?
It proves what can be shown in public: that for a published set of inputs we return a result you can reproduce by hand, and that the calculation passes our own compliance gate. It is not a notified body's certificate and we do not present it as one.
Will the numbers on this page change?
Only when the engine changes, and never quietly. The results are committed to the repository and compared against a live engine run every time the tests execute, so an engine change fails a test instead of silently rewriting this page.
Run your own house through the same engine
This calculation came out of the app, not out of a spreadsheet written for this page. Create a free account and calculate your own building - no card.