Heating Load Estimator
Estimate the design heating load of a room or building in kW and BTU/h from floor area, walls, roof, windows, floor, air changes and design temperatures — with a heat-loss breakdown per building element.
Input
Space
Envelope
Opaque wall only — exclude windows.
Use 0 for an intermediate floor.
Use 0 if heated space sits below.
5.7 single · 2.8 double · 1.4 low-e double · 0.8 triple.
Air & Conditions
Applies to mechanical ventilation only.
Output
| Metric | Value |
|---|---|
| No data yet | |
| Element | Loss (W) | Share |
|---|---|---|
| No data yet | ||
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/heating-load-estimator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"floorArea": "30",
"ceilingHeight": "2.7",
"wallArea": "25",
"wallU": "0.5",
"roofArea": "30",
"roofU": "0.3",
"floorLossArea": "30",
"floorU": "0.4",
"windowArea": "5",
"windowU": "2.8",
"infiltration": "0.5",
"ventilation": "0",
"heatRecovery": "0",
"outdoorTemp": "-5",
"indoorTemp": "21",
"safetyFactor": "15"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `heating-load-estimator` tool (Heating Load Estimator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/heating-load-estimator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Heating Load Estimator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
What this heating load estimator does
Sizing a boiler, furnace, heat pump or radiators starts with the design heating load: how much heat a building loses on the coldest expected day. This tool estimates it from floor area, walls, roof, floor, windows, air changes and the indoor/outdoor design temperatures. You get kW and BTU/h plus a table showing how much each building element loses — so you can see whether glass, walls or air leakage is driving the number.
How to use it
Enter the space (floor area, ceiling height), the envelope (area and U-value for walls, roof, floor and windows), air changes (infiltration, optional mechanical ventilation with heat-recovery efficiency) and the design temperatures. Results update as you type.
How it's calculated
Conduction (walls, roof, floor, glass) = U × Area × ΔT
Air loss = 0.33 × air changes/h × volume × ΔT
Ventilation loss is reduced by heat-recovery efficiency
Design load = total loss × (1 + safety margin)Internal gains from people and equipment are not credited, which is standard practice for a design-day figure. 1 kW = 3,412 BTU/h.
This is a screening estimate. It is a steady-state calculation, not a full EN 12831 or Manual J heat-loss survey. Use it for ballpark sizing and have a qualified engineer confirm before specifying equipment.
Frequently asked questions
What outdoor design temperature should I use? Use the 99% design temperature for your location — the cold level only exceeded about 1% of winter hours. Local weather services and building codes publish these.
What U-values are typical? Insulated modern walls 0.2–0.35 W/m²·K, older uninsulated masonry 1.5–2.0, double glazing about 2.8, low-e double 1.4, triple 0.8.
Why is the result per m² useful? Well-insulated new builds land near 30–60 W/m²; older homes often reach 100 W/m² or more. A figure far outside that range is a hint to recheck inputs.