Garden room or loft conversion: another radiator, or air conditioning?

This comes up most weeks. Someone has converted a loft, built a garden office or turned the old garage into a room, and now it is cold. The instinct is to run a radiator off the existing boiler. Sometimes that is right. Often it is not.

What extending the heating system really involves

Running a new radiator means getting flow and return pipes from the existing system to the new room. Across a hallway that is straightforward. Across a garden, under a floor slab, or up into a loft where the joists run the wrong way, it is not.

You also need to be honest about the boiler. Adding a radiator adds load. If the system is already marginal on a cold morning, the new room gets warm and one of the bedrooms stops doing so.

For a detached garden room the pipe run usually has to be buried and insulated, and at that point the groundwork costs more than the heating.

What an air-to-air heat pump does instead

A wall-mounted split system needs two things: a small hole for the pipe and cable, and an outdoor unit on a wall or on feet outside. No wet pipework, no extra load on the boiler, and a day's work rather than a week's.

Because it moves heat rather than making it, it typically returns three to four units of heat per unit of electricity. That compares well with a plug-in electric heater, which returns one, and it is the same box that cools the room in July.

When a radiator still wins

We fit both, so this is not a sales pitch for the newer thing.

Choose the radiator when the room is adjacent to existing pipework, when the boiler has capacity to spare, and when you want no visible indoor unit and no outdoor unit. Choose it also if the room is only occasionally used and the capital cost has to be as low as possible.

Choose the heat pump for a detached or hard-to-reach room, for anywhere that gets uncomfortably hot in summer as well as cold in winter, and for a home office that needs to be comfortable during the working day without heating the rest of the house.

The honest middle ground

A poorly insulated garden room will be expensive to keep warm whichever route you take. If the walls are thin and the glazing is single, spend the money there first. We would rather tell you that now than fit something that runs constantly and still disappoints.

Want someone to look at the actual room? Get in touch and we will give you a straight comparison, including the option we do not profit from.