The heat pump sizing module gives a preliminary output sizing for a conversation with the client: the recommended pump class, the supply temperature, SCOP, annual electricity consumption, installation cost and an assessment of whether the existing radiators are enough. It does not replace an installation design or an audit - a full design needs a site visit and measurements. This article leads through the wizard and explains how to read the result. Why a capacity margin is a mistake is explained in the guide on the oversized heat pump. What changed in the module in October is in the October 2026 update.
Two modes: from the heat loss calculation, or by hand
An empty module opens on the start screen "Size a heat pump with Algo" with the violet "Start with Algo" button and the "I'll fill it in myself" link under it; the "Guide" link in the top-right corner, opposite the back arrow, opens this article in a new tab. The module has two modes and proposes the right one:
- From the heat loss calculation. When the project has a heat loss result, the screen has three presses with the import first: the violet "Import the heat loss calculation with Algo", the framed "Import without Algo" and the "I'll fill it in myself" link. Under them a grey line names the source and its three figures, e.g. "Heat loss calculation: 7 rooms · 142.5 m² heated · 8.4 kW load". "Import the heat loss calculation with Algo" enters the heated area and the rooms (name, area, temperature) and stores each room's load from the calculation - the sizing runs from that load. The press then opens step 1 of the wizard and asks Algo what is still missing; Algo asks only for what the calculation does not hold: the number of residents, whether the pump also heats hot water, and the client's tariff. "Import without Algo" enters the same data and opens the wizard without Algo. If you open Algo some other way (e.g. from the Algo column) on an empty pump sizing while the project has a ready heat loss calculation, Algo offers the import itself: it says the calculation is ready and puts the "Use the heat loss calculation" press under its answer. When the project has a submitted client form instead, the first button is "Import the client form with Algo". If the heat loss calculation is incomplete or blocked, the line says so plainly and leads to it. If the heat loss calculation is finished only after you typed something in the pump selection, the gear on the wizard's bottom bar shows a 1, and the calculation waits in "Module settings", under "Data sources"; before it brings anything in, the app asks, because the heated area changes to the calculated one.
- By hand. "I'll fill it in myself" skips the calculation and estimates the load from the insulation class and year built - not recommended, but useful without data.
In both modes the wizard has four steps: "Building", "System", "Rooms", "Result", and every field stays editable. Bringing data in only adds: rooms you added by hand stay, and in the rooms from the calculation the radiators and underfloor heating you already entered stay as they were - only the name, area and temperature are overwritten.
When the heat loss calculation changes after the import, the module shows the "Heat loss calculation has changed" dialog with the list of changes on the next entry: you tick what to overwrite and click "Bring in the ticked values" or "Not now". In the module settings, under "Data sources", the "Heat loss calculation" row then reads "newer data available" with a "Bring in again (newer data available)" button. Details in data flows between modules.
Older projects linked to the calculation permanently move to this way of working by themselves on first opening. If an older project has a different load stored than the current calculation, the module shows the "The calculated heat loss has changed" dialog with the old and new values and the "Use the current load" and "Leave it as it is" buttons. A load above 100 kW is outside the module's range, and up to 50 rooms are imported from the heat loss calculation.
The Building step
In manual mode you enter the location (a design temperature from -16°C for Szczecin to -20°C for Warsaw, Kraków, Łódź and Katowice), the usable floor area, the year built or insulation level (before 1980, 1980-2000, 2000-2015, 2017+, 2021+), the ventilation type, the indoor temperature, the room height and the number of residents.
After an import from the heat loss calculation the step no longer shows the insulation class and year cards, the ventilation type cards or the room height field - with a calculated load the sizing does not use them. In their place stands one line: "Ventilation, room heights and the building envelope are already in the heat loss from the heat loss calculation - change them there." with the "Open the heat loss calculation" link. The section below, "Comfort and residents", holds the indoor temperature and the number of residents.
The "Sizing and tariff" section is in both modes:
- the bivalent point - the temperature down to which the pump works alone; monovalent sizing (no heater) by default,
- "Electricity price" - the field is never empty: it shows the national average the sizing uses, with a grey "Default - national average" chip; typing the client's tariff (G11/G12) removes the chip and makes the cost comparison theirs, and "Restore the national average" puts the average back,
- hot water - tick "The pump also heats hot water"; the pump's size gains the day's hot-water energy spread over 24 hours, about 0.09 kW per person (40 litres per person per day heated from 10 to 55 °C). The pump heats the house or the cylinder in turn, so the two powers do not add up. It needs the number of residents - without it the step shows "Enter the number of residents - without it hot water does not enter the sizing." and the result is for heating alone.
Bills and consumption (optional): the current heat source (gas, coal, pellets, wood, oil, electricity), annual consumption in the fuel's unit and the boiler efficiency. With these data the algorithm corrects the physical model (70%) with the bill history (30%); without them it works only from the building parameters. You enter the bills on the "System" step.
The System step
The heating distribution type: radiators (a higher supply temperature), underfloor (low temperature, ideal for a pump) or mixed.
The Rooms and Emitters step
Optional, but without it you get the pump sizing alone, with no radiator assessment. The rooms are open sections, one under another; on a phone you see one at a time, with a sticky "2 of 7" row and the room list sliding up from the bottom. For each room (up to 50) you give a name, area, temperature, height, optionally "Unheated", and then the emitters:
- radiators - type (11, 22, 33 or a bathroom towel rail), height, length and quantity,
- underfloor heating - pipe spacing (one of five values: 100, 150, 200, 250 or 300 mm; usually 200, in bathrooms 150 - any other spacing you type only in the underfloor heating module), floor covering and room type (standard up to 29°C floor surface, bathroom up to 33°C),
- both at once in a mixed room.
You add a radiator with "Add radiator", and the pencil beside a radiator opens it for editing. Both open the "New radiator" dialog (named after the radiator when editing): "Save" writes the radiator and "Cancel" discards the changes. The "Also save in My library" switch saves the radiator on your account too, and radiators from My library you pick in the "Type" field - the pick copies the type and dimensions. Choosing a towel rail sets the room temperature to 24°C - the dialog says so in a note, and the change applies only on "Save". When such a radiator is removed, the "Remove radiator?" dialog restores the previous temperature. The "Emitters in every room" section sets underfloor or radiators for the whole building at once; then you correct the exceptions. Changing the distribution type when rooms already have underfloor heating configured clears that data - the "Change distribution type?" dialog asks you to confirm with "Change and drop UFH data". Tick "This is the complete list of all heated rooms" only when every room has been entered - the algorithm then spreads the whole demand over the entered emitters; it is unticked by default, which is safer. Rooms brought in from the heat loss calculation you edit the same way as rooms added by hand; their calculated load is the basis of the radiator check.
The Result step
The header shows the preliminary output sizing: the recommended pump, supply, SCOP, annual consumption in kWh and installation cost. Below:
- "How this capacity was reached" - the sizing steps: design demand at the outdoor temperature, "Design margin", "Hot water" (when the pump also heats hot water), "Capacity required from the pump", output of the chosen pump at that supply and that outdoor temperature (nominal output drops with frost), headroom above the requirement, bivalent point and heater output,
- "Variants" - V1 "No radiator changes", V2 "Minimal replacements", V3 "Best efficiency", each with a pump, supply, consumption and cost; the recommended one is the feasible variant with the lowest installation cost,
- "Radiators & feasibility" - for each room the status OK, marginal or infeasible, with the missing output and the required supply, and the main cause of the loss (transmission, ventilation, bridges),
- "Operating point" - demand against pump output for the variants,
- "Annual cost" - a comparison with the current fuel at the given electricity price; the cost excludes the peak heater's work,
- "Warnings" and "Calculation notes" - among others warnings about a small output margin, about towel radiators, about low coverage of the area by rooms, about oversizing ("that is X times too much") and explanations of why a variant is infeasible,
- "Method and result confidence" - the load basis (the heat loss calculation or an estimate from the insulation class) and the model confidence: high, medium, low.
The remark "The radiator sizing solver is temporarily unavailable - the result is incomplete" means an outage of the solver on our side: the pump sizing is computed, the radiator assessment is not; come back to the result later.
The count icon on the wizard's bottom bar, beside the step number, collects what blocks the calculation (e.g. no area, no radiator dimensions); its "Gaps and warnings" window has "Fix" buttons. On the Result step two square icon buttons take the place of "Next": report notes and the report download; the tooltip gives their names ("Report notes", "Download PDF report"). Both are grey until there is a result - what is still missing, the Result step itself shows. See the article on reports.
Where the pump data comes from
The solver picks one of 10 generalised output classes (HP-4kW to HP-16kW). Their characteristics - output against outdoor temperature and supply, COP, costs - are averaged from the catalogue data of 239 devices by 28 manufacturers. It is a reference point for preliminary sizing, not a database of models to pick from; the result says "Catalogue: ... (N brands)", and a remark in the report reminds you to confirm the parameters of a specific unit with the distributor. The module is built for detached houses: the output classes go up to 16 kW, and when none reaches the required output the result suggests a cascade or reducing the building's losses.
Free account and report
On a free account you see the recommended pump with its parameters. The full list of matched pumps and the variant comparison (SCOP, annual usage, installation cost) are unlocked by a report, which covers the whole project - see what is free and what a report unlocks. You can also buy a report for heat pump sizing alone, for that project.
Module settings
The gear on the wizard's bottom bar opens the "Module settings" panel. The "Data sources" section has the source rows ("Heat loss calculation", "Client form") with a "Bring in" button and an "Algo AI" row with a "Fill in" button, which opens Algo with the start question. The "Module data" section has a "Clear data" row with a red "Clear" button. Until the load has come in through "Data sources", the panel also has a "Heat loss source" section (From the calculation or Own data, with the "Use the heat loss calculation" and "Unlink from the calculation" buttons). At the bottom a grey line states the module's scope: "Preliminary sizing for a client discussion".