Precise calculations
Formulas grounded in real energy rates, climate and building data.
Free HVAC & energy tools
Right-size your HVAC with free calculators
Professional AC sizing, heating costs, heat pumps, solar and radiators — free results, no sign-up. Optional PDF reports when you need them.
- Free results
- No sign-up required
- 13 languages
Annual savings
ExampleAnnual savings
£0
35% cost reduction
Current annual cost
Before£0
After£0
Payback period
0.0years
Optimized system
£0
Browse calculators
Illustrative only — your results use local rates and building data.
What do you want to decide today?
Pick a goal and jump straight into the right calculator.
Cooling & AC size
Find the right BTU/kW before you buy or install.
Open toolHeating costs
Estimate monthly and annual heating bills from real usage.
Open toolCompare heating systems
Heat pump vs gas, oil or electric — savings side by side.
Open toolCheck solar potential
Size PV panels, battery and bill savings.
Open toolPlan for business
Commercial heating and LED audit tools.
Open toolFeatured calculators
Start with the tools that drive the biggest HVAC decisions.
FREE
AC sizing
Find the right BTU/kW for any room or building before you buy.
FREE
Heat pump ROI
Compare heat pump savings vs gas, oil or electric heating.
NEW
Solar panel sizing
Estimate kW, panel count, battery and annual production.
PRO · $9.99/mo
Radiator Pro
Professional heat-loss workflow and 3D room view. Calculator subscription — unlimited PDF reports require Thermopy Premium.
How Thermopy works
From building details to installer-ready numbers — in three steps.
- 1
Choose a calculator
Pick AC sizing, heating costs, heat pump ROI, solar or radiators.
- 2
Enter your data
Add room size, climate, insulation and energy rates. Results update instantly.
- 3
Compare and act
See costs, savings and recommendations you can share with installers.
Free tools, paid reports when you need them
Start free. Add a one-time PDF or subscribe only if you need Pro workflows and unlimited reports.
Free calculators
$0
Instant results for homes and light commercial — no account required.
- 18 live HVAC & energy calculators
- Metric & imperial units
- 13 languages
Installer PDF report
$9.99
One-time AC, Cooling or Solar PDF you can share with installers.
- System recommendation & savings
- Email delivery in minutes
- No subscription required
Radiator Pro
$9.99/mo
Unlock advanced radiator calculator features — not unlimited PDF reports.
- 5-step heat-loss workflow
- 3D room visualisation
- PDF reports need Thermopy Premium
Thermopy Premium
$29.99/mo
Unlimited PDF reports plus all professional calculator features.
- Unlimited AC, Cooling & Solar PDFs
- Includes Radiator Pro access
- Cancel anytime
Why choose Thermopy
Professional HVAC tools for accurate cooling, heating and solar decisions.
System comparison
Compare heating and cooling options side by side before you invest.
Clear cost breakdowns
Monthly, seasonal and annual views you can share with installers.
Energy optimization
Spot oversized equipment and upgrades that actually cut bills.
If Thermopy helped you, consider sharing your experience on Trustpilot.
Guides that link to calculators
Practical HVAC guidance with a clear next step into the right tool.
Available in 13 languages
Frequently asked questions
Quick answers about Thermopy calculators, reports and plans.
How accurate are the calculators?
They use professional formulas and real-world energy rates for reliable planning estimates. Final equipment selection should still be confirmed by a qualified installer.
Which calculator should I start with?
For cooling, start with AC Sizing. For winter bills, use Heating Costs or Heat Pump ROI. For solar, open Solar Panel Sizing. For radiators, try Radiator Pro.
Do I need an account?
No. Free calculators work without an account. Create one only if you want to save results or unlock paid reports and subscriptions.
Are BTU and kW both supported?
Yes. AC and cooling tools support metric and imperial units so you can work in BTU/h, tons or kW.
How much does a PDF report cost?
Installer PDF reports for AC, Cooling Comparison and Solar Sizing are $9.99 one-time each. No subscription required.
What is the difference between Radiator Pro and Thermopy Premium?
Radiator Pro ($9.99/month) unlocks the advanced radiator calculator. Thermopy Premium ($29.99/month) includes Radiator Pro access plus unlimited PDF reports across AC, Cooling and Solar.
Is Thermopy really free?
Core calculators are free with no sign-up. Optional one-time reports and subscriptions are clearly priced when you need them.
Which languages are available?
Thermopy is available in 13 languages with localized units and copy. Switch language anytime from the header.
Ready to get the right numbers?
Browse every free calculator — or view plans if you need PDF reports and Pro tools.