Advice · 4 min read · Updated 6 November 2026
Where is the best place to put a radiator? Under windows and beyond
Why radiators ended up under windows
For decades, the window was the coldest part of a room. Cold air sinks down the glass and spreads across the floor, creating a draught. A radiator underneath warms that air as it falls and pushes it back up, which makes the room feel more comfortable. Windows also take up wall space you cannot use for furniture, so it was a practical choice.
With modern double glazing the downdraught is much smaller, so the case for the window position is weaker. It is still a good default, but no longer the only sensible option.
Comparing the common positions
| Position | Pros | Cons |
|---|---|---|
| Under a window | Counters cold draughts, uses dead wall space | Long curtains block heat, more heat lost through glass behind |
| Internal wall | Less heat lost through the wall behind | Takes up wall space you might want for furniture |
| External side wall | Often frees up the window area | Some heat lost through the wall unless well insulated |
| Vertical radiator on a narrow wall | Uses tall slim spaces, good for small rooms | Can have lower output for its footprint, needs careful sizing |
| Behind a door | Out of the way | Door may block heat, risk of being knocked |
Rules of thumb for clearances
Manufacturers publish their own fitting instructions, and these should always be followed. As a general guide, radiators perform best with a gap under them so cool air can be drawn in at floor level, and a gap above if there is a shelf or windowsill. A deep sill directly over a radiator can trap warm air and push it out of the window recess.
- Leave a clear gap under the radiator so air can flow in
- Avoid placing sofas or beds tight against the front
- Keep long curtains clear of the radiator or tuck them behind the sill
- Radiator covers and shelves cut output, so size up if you use them
- Leave enough room either side to get to the valves
Room by room advice
Living rooms often benefit from two smaller radiators rather than one large one, especially in through-lounges with a window at each end. This spreads the heat and leaves more wall free for a TV or sofa.
Kitchens rarely have spare wall space. Vertical radiators, a plinth heater under units or a radiator on the end wall are common answers. Avoid fitting a radiator where tall units or appliances will sit directly in front of it.
Bedrooms usually work well with a radiator under the window, provided the bed does not end up pushed against it. Bathrooms usually use a towel rail, and it is worth checking it gives enough heat for the room rather than just warming towels.
Hallways in older houses often lose heat through the front door. A radiator close to the door, rather than at the far end of the hall, helps counter the draught.
Pipework: what makes a move easy or hard
Moving a radiator a short distance along the same wall is often straightforward. Moving it to another wall can mean lifting floorboards, running pipes under the floor or chasing them into the wall. On solid concrete floors, pipes may need to run on the surface behind boxing or skirting, or be chased into the floor, which adds cost and mess.
- Suspended timber floor: pipes usually run under the boards, a relatively simple move
- Solid floor: surface pipes or chasing, more disruptive
- Upstairs: pipes often run between joists, access from above is usually fine
- Microbore systems: small pipes can be easier to route but may limit output
Mistakes people make when choosing a spot
- Planning a radiator position before the furniture layout is settled
- Choosing a slim vertical radiator for a large room without checking its output
- Placing a radiator where a door will open into it
- Fitting a radiator behind a built-in seat or cupboard
- Ignoring where the thermostat is, so one room's heat affects another's control
A sketch of the room with doors, windows, sockets and furniture marked is the quickest way to spot clashes before any pipes are moved.
If you are redecorating or replacing flooring, that is the cheapest moment to move a radiator, because boards are already up and walls will be made good and painted anyway. Moving one later means repeating some of that disruption.
Frequently asked questions
Is it inefficient to put a radiator on an external wall?
A radiator on an external wall loses a little more heat through the wall behind it than one on an internal wall, especially in solid-walled older houses. In well insulated homes the difference is small. Reflective panels behind radiators on uninsulated external walls can help a little. Comfort and room layout are usually more important deciding factors than this small loss.
Can a radiator go behind a sofa?
It can, but the sofa will block much of the heat and the room may feel cooler. If there is no alternative, leave a gap of several inches between the sofa and radiator, and consider a larger radiator to make up for the restricted airflow. Fabric pressed against a hot radiator can also become discoloured over time, so keep a gap.
Do vertical radiators give out less heat?
Not necessarily, but many slim vertical models have a lower output than a horizontal panel radiator covering the same wall area. Always compare the output figure, usually given in watts or BTU at Delta T50, against the room's needs. Double panel vertical radiators are available for rooms that need more heat from a narrow space.
radiator position moving radiators room layout efficiency
