🖤 BLACK FRIDAY SALE · ENDS FRIDAY 27 NOVEMBER
SMART HEATING SOLUTIONS
SMARTER HEATING | LOWER BILLS
🖤 BLACK FRIDAY SALE
25% off our top 4 radiators
Plus 15% off everything else in store. Ends midnight, Friday 27 November. 5-year warranty and free standard delivery on every radiator.
BTU Calculator – what size radiator do I need?
Answer a few quick questions about your room and we'll work out the heat output you need, then show you the radiators that fit.
BTU/hr
watts · at ΔT50
Radiators that match your room
Send us your room details on WhatsApp and we'll help you pick the right radiator.
How does this calculator work?
We work out how much heat your room loses on a cold winter day, the same way a heating engineer does. We add up the heat lost through each outside wall, window, door, floor and ceiling (using typical U-values for each type of construction), plus the heat lost through draughts and fresh air. We then add a 20% margin so the room warms up quickly from cold. Your result is never lower than the standard size-based guide most UK radiator retailers use (room volume × 4–5 BTU per cubic foot), so you won't end up with a radiator that's too small.
Each room is heated to the recommended temperature for that room (21°C for living rooms, 22°C for bathrooms, 18°C for bedrooms, kitchens and hallways), on a typical cold winter day for your part of the UK.
All results are given at ΔT50, the UK standard for radiator outputs, so you can compare them directly with the BTU figures on our product pages. If you have a heat pump or a low-temperature boiler, your radiators run cooler, so we increase the ΔT50 output you need to make up for it.
This calculator is a guide. For a new build, an extension or a full heating system design, we'd always recommend a room-by-room heat-loss survey by a qualified heating engineer.
Radiator Inspiration from Our Customers
From choosing to checkout
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Step 1
Choose your radiator
Browse the range and choose the style and size for your space.
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Step 2
Check the details
Review the dimensions, heat output and product information before ordering.
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Step 3
Add to your basket
Select your items and check the quantities in your basket.
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Step 4
Choose your payment method
Continue to checkout to see the payment options available for your order.
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Step 5
Complete your order
Review your delivery details and order total before confirming your purchase.