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Heating · RadiatorsRadiator Installation & Relocation
Radiator installation and relocation turns on two numbers: how much heat the room loses and how hot the water will be. A cast-iron radiator gives about 150 BTU per square foot of rated surface at 77°C average water and roughly 60% of that at 60°C, so a radiator that suited an old boiler can come up short on a condensing one unless it is sized for the cooler water.
Sizing starts with the room, not the radiator. We work out the room's heat loss from its walls, windows and insulation, then pick a radiator that delivers that much at the water temperature your boiler will run. This matters most with a condensing boiler, which only condenses when the water returning to it is below about 55°C. Radiators generous enough to heat the room on cooler water are what let that boiler reach its rated efficiency, a trade-off laid out in cast-iron versus condensing boilers.
Renovated pre-war houses usually have more radiator than they need. Cast iron chosen when the walls were uninsulated and the windows single-glazed is oversized for the same room after new windows and attic insulation, which is good news: it can run on cooler water. A new addition or a finished attic is the opposite case and needs its own calculation. New radiators can be reclaimed cast iron to match the house, or steel panels that respond faster and hold far less water.
Moving or removing a radiator for a renovation is a drain-and-refill job. The system, or the part of it above the work, is drained and the radiator disconnected; a large cast-iron one can weigh well over 100 kg, so it is a two-person lift with the floor protected. Pipes are rerouted in copper or oxygen-barrier PEX, the system is refilled, every radiator is purged of air and the pressure is reset. If a radiator is leaving for good, we tell you before the wall is closed whether what remains will still heat the room.
How a new radiator ties in depends on the piping. In a two-pipe system it gets one tee into the supply main and another into the return, and the system is rebalanced afterwards. In a one-pipe system both connections come off the same main through diverter tees, and their spacing and direction decide whether water goes through the radiator at all. Send photos of the boiler and the nearest radiators and we can usually tell which you have before the visit.
Jobs this service covers
- Adding a radiator to an addition, a finished attic or a basement room on the existing boiler
- Moving a radiator off a wall that is coming down, or out of the way of new kitchen cabinets
- Lifting radiators out so floors can be refinished or walls plastered, then reconnecting them
- Swapping a cracked cast-iron radiator for a matched reclaimed unit or a steel panel
- Removing a radiator permanently and capping its branch so everything else still circulates
How it works
The room is measured, its heat loss calculated, and the piping traced back to the mains to see whether the system is one-pipe, two-pipe or a series loop. The quote names the radiator, its output at your water temperature and the pipe route.
The system is drained to below the work, old branches are capped or extended, and the radiator is set level on its feet or brackets with a valve on the supply and a lockshield on the return.
The system is refilled and brought to pressure, air is bled from every radiator and not only the new one, and the lockshields are adjusted so the addition does not rob the rooms next to it.
Common questions
What does it cost to add or move a radiator?
We do not publish a flat figure because four things move it: the radiator itself, the distance from the nearest supply and return mains, how much finished floor or ceiling has to be opened for pipe, and whether the whole system or only one zone has to be drained. A site visit produces a written price. Our pricing page lists the bands we do publish.
Can radiators be moved in the middle of winter?
Yes, but the house has no heat while the system is drained, so we plan it for a mild day, pre-build what we can, and isolate the work to one zone where valves allow. Renovation moves are best booked between April and October. If pipes will sit drained in an unheated space, read what to do if heating pipes or radiators freeze.
Will my old radiators work with a new condensing boiler?
Usually, and often well. We count the sections, measure the height and column pattern to get each radiator's rated output, then compare it with the room's heat loss at cooler water. Where the radiator is oversized, the boiler can run in its condensing range most of the winter. Where one room is short, that radiator is upsized instead of running the whole house hotter.
Can I just cap off a radiator I no longer want?
On a two-pipe or diverter-tee system, yes: both branches are capped and flow carries on along the mains. On a series loop the radiator is part of the only path, so the pipe has to be bridged or everything downstream goes cold. Either way the room loses its heat source, and water pipes in its outside walls lose their protection too.
Should valves be upgraded while the system is drained?
It is the cheapest moment to do it, because the drain-down and refill are already paid for. Seized hand valves can be replaced, and thermostatic radiator valves fitted for room-by-room control. If the boiler itself is near the end of its life, boiler repair and installation is worth pricing in the same plan so the system is only opened once.