The heat load module calculates the building's design heat load room by room to EN 12831-1:2017, with the thermal resistance of envelopes to EN ISO 6946 and heat exchange with the ground to EN ISO 13370. The wizard leads through seven steps, and the result is computed live as soon as you enter the area and the rooms. This article describes each step, the compliance status and what a report unlocks. What a heat load calculation is in physical terms and what depends on it is explained in a separate guide: what a heat load calculation is.
Before you start: data from the form and from Algo
If the client filled in the form, on entering the module you see the card "Before you start - This is what we already know about the project" with the "Bring it into this module" button; the building data and the room list fill in by themselves. You can also upload building documents to the Algo assistant - it proposes values for the fields. Both sources are described in data flows between modules.
Step 1: Project
You click on the map the city nearest the building (Warsaw, Kraków, Gdańsk, Wrocław, Poznań, Szczecin, Łódź, Katowice) - this sets the climate zone and the design outdoor temperature from the national table. You can override it if you have more accurate data. You also enter the heated area, that is the sum of the heated rooms' areas; if the sum of rooms from step 5 exceeds it, you get a warning.
Step 2: Building
Data shared by the whole building:
- the dimension basis - internal (between walls, the most common for detailed designs), external (outlines) or measured; measure envelopes consistently on one basis,
- thermal bridges - the construction class adds a blanket ΔU_TB: very good 0.02, standard 0.05, retrofitted 0.10, poor 0.15 W/(m²·K),
- airtightness - class I-IV suggests a typical value, and if you have a Blower Door result, enter n50; above 3 1/h the app suggests switching to the detailed method with per-room flows.
Step 3: Ventilation
You choose the type: natural, mechanical extract, or mechanical with heat recovery. With heat recovery the recovery efficiency field appears (85% is typical for a good unit) and the "Insert default airflows" button, which fills supply and extract in the rooms with typical values; fields already filled are not overwritten. The air change rate defaults to 0.5 1/h. If the project has a designed ventilation system in the ventilation module, the heat load calculation checks consistency: the ventilation type, the efficiency and the room flows must agree.
Step 4: Envelope library
Here you save layer build-ups for the project so you do not enter them in every room from scratch. "Choose a ready envelope" offers typical constructions (25 cm ceramic block + 20 cm graphite EPS wall, silicate + mineral wool, aerated concrete with and without insulation, a pitched roof with wool, floors on the ground with EPS or XPS, a ceiling under an unheated attic, an internal wall to an unheated space). Each one can be edited: layers from the inside, thicknesses, materials from the list (EPS, wools, bricks, blocks, concretes, plasters, boards) with their own λ. Ready envelopes are proposals - check thicknesses and λ against the building documentation, because the result matches reality only when the layers reflect the real cross-section.
Step 5: Rooms
Most of the work is here. "Add room" creates a card with a name, a type (living room, bedroom, kitchen, bathroom 24°C, corridor 18°C and others, office and service rooms too), area, height, design temperature and storey (basement, ground floor, upper floors). "Choose typical values" sets the temperature and ventilation category with one click. A room can be duplicated, and "Add attic" runs the wizard that generates slopes, knee walls, gables, floor and collar tie ceiling from the building width, roof angle, knee wall and length.
In every room you add envelope elements: external wall, roof, floor on the ground, ceiling under an unheated space, floor above an unheated space, wall to an unheated space, internal ceiling. For each you enter the gross area (with openings - windows and doors from the table subtract themselves, and losses are computed from the net area) and the U-value: directly or from layers copied from the library. Non-homogeneous walls (timber frame with studs) have their own mode with a structural fraction.
The details the standard asks about:
- floor on the ground - perimeter P and depth z; without a measured perimeter the app assumes 4·√A and lowers the compliance status; the groundwater level affects the f_GW correction,
- envelopes to unheated spaces - you pick what is on the other side (a room with 1-3 external walls, a basement, an insulated or uninsulated attic, a circulation space, a suspended floor void) and the b_u factor follows; you can also give an exact temperature,
- windows and doors - a table with width, height, U and quantity,
- the ventilation category - a habitable room or a wet room with a window (n_min 0.5) or an internal secondary room (0.0); with heat recovery also supply and extract,
- high rooms (from 4 m) - a heat emission system must be selected.
Step 6: Adjustments
For a typical detached house you can skip this step. It holds internal heat gains (ignored by default; non-zero values are an explicit assumption to agree with the client, with a per-room override), intermittent heating with the heating-up power φ_hu (from the auxiliary table or entered by hand, with the setback period, the air change during setback, the building's thermal mass and the heating-up time) and the heat source sizing correction - a factor that helps size the source and deliberately does not change the rooms' loads.
Step 7: Result
The result shows the building's design heat load, the heating output index in W/m², the heated area and the split into transmission, ventilation and thermal bridges. The "Room breakdown" carousel switches rooms, and clicking a card opens the details: envelopes with layers and the U computation, windows and doors, load components, ground corrections, ventilation. The "Calculation method" tab describes the assumed parameters. From here you download the PDF - see the article on reports.
You also see the live result in the panel beside the wizard from step 1 on ("Live result"), as soon as you enter the area and the rooms.
Issues, blockers and the compliance status
The "N to fix" chip above the wizard collects everything that needs completing. Items labelled "Blocks the calculation" (e.g. no rooms, a room without envelopes, heated area exceeded, missing flows with mechanical ventilation) stop the calculation; the "Fix" button takes you to the field. The remaining remarks do not block the result but lower its status.
The status on the result has two values: "Result meets EN 12831-1:2017" or "Approximate result - does not meet strict EN 12831-1 compliance". You see the reasons in the "About this result" dialog: an approximate perimeter of the floor on the ground, missing air flows, heating-up power from the table without confirming the conditions of Annex F.2, the old temperature correction factor. A project with air transfer devices between zones (ATD) or designed flows between rooms is outside the module's scope - the app says so plainly.
What a free account shows
The calculations run in full. On screen and in the PDF you see the building's demand, the index and one fully calculated room; the other room cards show "Value available once the project is unlocked", and the method details (source sizing, bridges, n50, ventilation) wait for the unlock. One report unlocks the whole project - see what is free and what a report unlocks.
Module settings and clearing data
The module settings icon opens a panel with the module description ("About this module"), the "Data sources" section (import from the client form) and "Module data" with the "Clear data" button, which wipes the whole heat load form in this project after confirmation. The heat load result feeds pump sizing, underfloor heating and ventilation - after changes in the heat load calculation those modules offer an update.