The Radiators module answers one question: will the radiators in a house give each room the heat it needs at the water temperature you choose? That matters before a heat pump, because a heat pump runs cheapest at a low flow temperature. The wizard has five steps: Setup, Radiators, Rooms, Network and Result. What the module does is on the Radiators page.
Units in the US
An account created from the US starts in imperial units: the fields show square feet, °F, inches and Btu/h. You can switch in Settings. The calculation itself stays in SI units. Radiator sizes in this article are in millimeters, as the makers' datasheets print them, and the rating point 75/65/20 is in °C, as every datasheet gives it.
Step 1: Setup
In "What you are doing" you pick "Checking existing radiators" - the module tells you at what temperature they are enough and which to swap - or "Sizing new radiators" for a new house; then you also choose "New radiator type" and "New radiator height".
In "Water temperature" you set "Flow temperature" (from 86 °F (30 °C) to 176 °F (80 °C)) and "Flow-return difference". You choose both values, and both print beside the result.
The room loads are in "Module settings" (the gear). When the project has a heat loss calculation, "Take rooms and loads from Heat loss" brings in the rooms with their loads calculated to EN 12831-1; after a change there, use "Refresh from Heat loss". Without it the module estimates the loads from "Heated floor area", "Building insulation" and the temperatures, and the screen and the report say so: "An estimate from the floor area, not a calculation to EN 12831-1." Where these numbers come from is in Radiator output: where the numbers come from.
Step 2: Radiators
Here you describe the radiators that hang in the house once - the rooms then pick them from the list. The list is split by kind: "Panel radiators", "Towel rails", "Column and cast iron" and "Other". The plus beside a kind (e.g. "Add a panel radiator") opens the dialog: "Name", "Type" (for a panel 10, 11, 20, 21, 22 or 33), "Height" and "Length". You can also take a radiator from My library, and "Also save to my library" keeps it for your next projects.
Have the maker's datasheet? Tick "I have the radiator's datasheet" and type "Datasheet output at 75/65/20" and "Exponent n" - the radiator then says "datasheet". Without one a panel radiator's output is "typical": the median of several makers' datasheets for that type and height. A radiator with no datasheet output and no panel type is "assumed" - counted as a type 22 panel of its size. Algo AI adds radiators from a description, an old design or a photo - see A radiator from a photo.
Step 3: Rooms
Rooms from the heat loss calculation are already here; you add others with "Add a room". Each has "Name", "Area" and "Temperature" (empty means as the house). A "Typed load" beats the heat loss calculation and the estimate. Mark a room with no heating as "Unheated room"; when the Network step has floors, also pick its "Storey".
"Add a radiator" opens the dialog. In "Radiator" you pick one of the house's radiators from the Radiators step; "Its own size" opens "New radiator in this house", adds a new radiator to the house's list, and the row takes it. Then "Count" and "Wall space" - the longest radiator that fits there, which is the most a swap may be (an empty field counts as 2000 mm). In "Sizing new radiators" mode the module sizes new radiators and takes only the "Wall space" from the row. A radiator stored with its size only (an older project or one Algo added) reads "Described in this room only" with "Save as a type".
Step 4: Network (for the designer)
The radiator result does not need a network - if you only check radiators, go to the Result step. The designer calculates a two-pipe system here:
- "Add a storey" with its "Floor level" - the riser length comes from the difference.
- "Load the plan" (an image or a PDF, up to 25 MB) and "Set the scale". Without a plan you draw on a 1 m grid.
- Place "Heat source", "Junction", "Radiator", "UFH manifold" and "Separator" and join them with pipes - one line is a pair: flow and return. A manifold from this project's radiant floor heating takes its flow and loop drop from it ("From underfloor heating"). A radiator lies horizontal or vertical: "Direction" in its panel ("Horizontal", "Vertical"), the rotate handle or the O key - the drawings turn it too.
- Fill in "Designer's assumptions" - values the designer adopts, not from a standard - in "Module settings" (the gear); a floor keeps only its "Floor level". Without them no pipe is sized, and the note about a missing value opens the settings.
The pump head, the total flow and the index circuit are free. The pipe sizes and each valve's "Required Kv" come with the report.
Step 5: Result
At the top is one sentence about the whole house, e.g. "Your radiators heat the house at 126 °F (52 °C)." - the lowest flow temperature at which they are enough in every room - and how many rooms are short at the temperature from Setup. That is free: change the temperature and see how many rooms are then enough.
The report unlocks a card for every room: "Needed" beside what the radiators give at the chosen temperature, "Enough from" and "What to swap to" - the smallest change that is enough and fits the "Wall space". Under the result is the method line (the EN 442 characteristic, without mounting factors and without heat from pipes) and the sentence "A radiator check, not an installation design."
Downloads
On the Result step, "Download" opens one menu, "Downloads":
- "PDF report" - the "Full", "Simple" and "Custom" versions, see PDF report: full or simple. Without a report you get the watermarked preview.
- "Materials list (PDF)" and "Materials list (Excel)" - an enquiry for a wholesaler: radiators, valves, pipes and fittings, with no brands and no prices. Pipe in "Steel - existing" (steel already in the house) counts as rougher (PN-M-34034, Table I-1) and is not ordered, nor is its insulation; a tee or transition joining it to new pipe is.
- "Drawings (PDF)" and "Drawings (DXF)" - plans and schematic, A3 1:50, once a network is drawn.
Without the module unlocked, the materials list and the drawings sit in the menu marked "In the full report".
Free account and the report
Free, you get the house's flow temperature, how many rooms are short and the pump head of the network. Every room and the radiator to swap to, the pipe sizes and valve Kv, and the PDF report, materials list and drawings come with a report - for the Radiators module or for the whole project. What is free in each module is in free plan and what a report unlocks, and the prices are on the pricing page.
A HeatAlgo report follows EN 12831-1 and EN 1264, not ACCA Manual J, and is not accepted for permits or rebates.