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.
Two modes: from the heat load calculation, or by hand
The module has two modes and proposes the right one on entry:
- From the heat load calculation. When the project has a heat load result, the start screen shows the building's heat load, the number of rooms, the area and the design temperature ("Heat load calculation · EN 12831-1") and the "Start pump sizing" button. The building and rooms come from the calculation and update together with it. The wizard has three steps: "Building (calculated)", "Emitters", "Result". The "Data from the heat load calculation" chip in the header is a reminder of the link. If the heat load calculation is incomplete or blocked, the module leads to it with the list of things to fix.
- By hand. "Continue without a calculation" estimates the load from the insulation class and year built - not recommended, but useful without data. The wizard has four steps: "Building", "System", "Rooms", "Result".
You can break the link with "Unlink from the calculation" in the module settings - the current values are copied into the form and become editable, but further changes in the heat load calculation no longer arrive here. Conversely, "Use the heat load calculation" links the module again. When the load in the heat load calculation changes after linking, the module shows the old and new values with a "Use the current load" button. A load above 100 kW is outside the module's range, and up to 50 rooms are imported from the heat load 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. In linked mode those data are read-only, and you enter what the heat load calculation does not know: the insulation class as information for the report, the number of residents and the bills.
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,
- the electricity price - an empty field means the national price; the client's tariff (G11/G12) makes the cost comparison theirs,
- hot water - tick "The pump also heats hot water" and give the tank reheat power; without a number of residents the hot water demand is not estimated, which a remark in the result says.
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. In manual mode the bills are on the "System" step, in linked mode on the "Building" step.
The System step (manual mode only)
The heating distribution type: radiators (a higher supply temperature), underfloor (low temperature, ideal for a pump) or mixed. In linked mode this step does not exist - the distribution follows from the emitters entered in the rooms.
The Rooms and Emitters step
Optional, but without it you get the pump sizing alone, with no radiator assessment. 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 (100-300 mm; usually 200, in bathrooms 150), floor covering and room type (standard up to 29°C floor surface, bathroom up to 33°C),
- both at once in a mixed room.
Choosing a towel rail sets the room temperature to 24°C - the app asks about it in the "Change radiator type?" dialog, and when such a radiator is removed it asks again and returns to 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. In linked mode the rooms come from the heat load calculation and cannot be added or removed here - you only add emitters.
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, output 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 load 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 "Gaps and warnings" chip above the wizard collects what blocks the calculation (e.g. no area, no radiator dimensions) with a "Fix" button. At the bottom of the step is the "Report notes" field and the "Download PDF report" button - 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.
Module settings
The settings icon opens a panel: "About this module", "Scope", "Heat load source" (From the calculation or Own data, with the "Use the heat load calculation" and "Unlink" buttons), "Data sources" (parameters from the client form) and "Module data" with the "Clear data" button.