Trade Radiators Heating Calculator
To help make choosing a radiator suitable for your home easier, the Trade Radiators heating calculator will predict the necessary heat output (in BTUs and Watts) required to maintain a comfortable room temperature. These values are listed with all the radiators we sell on the site to help shortlist suitable products for you. To help you better understand how, where, why and when you'd use this calculator, we've answered some popular questions about BTU, the heating calculator, how it affects your home and how it works.
What does this calculator do?
Why do I need a heating calculator?
What exactly is BTU?
A radiator can be the wrong size?
What measurements do I need?
And to help clear any confusion of what qualifies as width and length, the length of a room (top to bottom) will almost always be longer than the width (side to side).
Why does the type of room matter?
Different rooms have different features and items that need to be accounted for. For example, you'd be surprised how many living rooms have a great big radiator but hide it behind a sofa that draws in all the heat. Kitchens are generally tiled or laminated and often a room where doors in and out of the house are constantly being opened and closed, meaning they need a high BTU to stay warm.
The same goes for hallways which will have the highest height, smallest width and most exposure to the cold outside with the front door opening and closing.
Why does what is below the room matter?
For any rooms upstairs, the BTU will usually be lower as the natural heat rising up from the ground floor, combined with insulated floors and carpeting mean that spaces like your bedroom can hold heat pretty well.
When we're on the ground floor, heat efficiency can be altered if you have soil under a wooden floor, the soil under concrete or a suspended floor. What goes on under your floor is very important as a badly ventilated underfloor can cause condensation or contaminated air to build up. Many modern homes will have their own extended underfloor vent to help circulate heat.
If you walk around the outside of your house and see that one of the bricks on the lower wall has a brick-ish coloured plastic grill over it, you have a suspended floor and that is the vent coming from it. If you know that under your wooden floor or carpet is just a large hard grey floor, you have soil under a solid concrete floor.
Why does what is above the room matter?
- Heated room
If your bedroom or bathroom sits above any used room below, then they're above a heated room. This means that heat coming up can help act as a buffer of sorts for your room.
- A pitched insulated roof
If your attic is above and not insulated, your room may already be very sound heat-wise or need a powerful radiator to keep the space warm.
- Pitched roof insulated 50mm
Thinly insulated roofs are usually a sign that your rooms on the upper floor have good insulation already.
- Pitched roof insulated 100mm
A thickly insulated roof will be a sign that your room has had issues with heat, but this insulation should help it stay warm quite easily.
Why does the type of outside walls matter?
Figuring out which walls you have can be easy. If the bricks alternate from row to row, then you're likely to have cavity insulation. Now if your wall has been covered over and you can't see the brick, just go to an outside wall with a window in it. If you can confidently say that the wall is thicker than 26cm it will have a cavity in there. If it is much thinner or clearly thicker than that, it could be a solid brick wall. And if you're wondering what a wooden frame wall is, it's just an old wall that is supported in some part by a timber frame, but this is usually only ever-present in very old homes.
Why does the type of windows matter?
Many modern homes will have double glazing which does help retain a lot of heat and bring the BTU down.
Why does the number of outside walls matter?
The outside walls will almost always be where heat has the least trouble escaping. That's why in many homes you'll find that the living room radiator is either against an internal wall where it requires the least resistance to heat up or on the exterior wall underneath your big window where it can force a floor draught upwards towards it. This stops the room from feeling cold all the time through convection (as many people don't realise that radiators convect heat and do not radiate heat).