Hot Water Cylinder in the Loft: Can It Go Up There?

Why people want the cylinder in the loft

Usually to get a cupboard back. In a lot of London flats and terraces the airing cupboard takes a slice out of a bedroom or a landing, and moving the cylinder upstairs frees it for storage or a larger bathroom. Loft conversions are the other common reason: the old cold tanks come out when the loft becomes a room, and the eaves space behind the knee wall is the obvious place for a new unvented cylinder.

Sometimes the cylinder is already up there, left over from an older layout, and the question is whether to replace it in the same place. The same checks apply, with one advantage: the platform and the pipe routes already exist, and an engineer can see whether they were done properly.

The five things that decide it

Every loft cylinder we survey comes down to the same list. Any one of them can turn a reasonable job into the wrong one.

• Weight: a full 210 litre cylinder weighs well over 200 kilos, concentrated on a small footprint
• Discharge: the pipe from the safety valves has to fall continuously to a safe termination outside
• Frost: an unheated roof space can freeze the pipework and the valves on the cold feed
• Access: fixed ladder, boarded route and light, so the annual service can actually be done
• Getting it in: the cylinder, and the old one if it is coming down, has to pass the hatch and the stairs

Weight and the ceiling joists

Loft floors are usually ceiling joists, sized to hold up a plasterboard ceiling and some storage, not a point load of a quarter of a tonne. A cylinder in a loft has to sit on a proper platform spread across several joists, and ideally bearing close to a load bearing wall rather than in the middle of a span.

For a large cylinder, or where the joists are small or have been notched for old pipes and cables, the safe answer is to have the structure looked at before anything is ordered. That is not us being cautious for the sake of it. A failed platform with a full cylinder on it ends up in the room below.

In a converted loft the floor is normally built to take room loads, which helps, but the eaves space behind the knee wall may still be the original ceiling joists. Check which one the cylinder will actually stand on.

The discharge pipe is often the hardest part

An unvented cylinder has safety valves that can discharge very hot water if something goes wrong. That water goes through a tundish, which has to be visible and close to the cylinder, and then along a discharge pipe that must keep falling all the way to a safe termination outside where nobody can be scalded.

From a ground floor cupboard that can be a short run through an external wall. From a loft it can mean a long run down through the house, and long runs have to be increased in size so they can still carry the discharge. Every bend counts against the allowed length. On some houses there is a sensible route out through the roof line and down, on others there is not, and the discharge route is what makes a loft position impossible.

This is where a quote priced over the phone goes wrong most often. Ask anyone quoting a loft cylinder exactly where the discharge will run and where it will end. If they cannot tell you, they have not looked. The tundish is the part of this you can see, and if yours is ever wet, our page on a tundish dripping explains what it is telling you.

Fitting an unvented cylinder is notifiable building work and must be done by an engineer holding the unvented hot water qualification. That applies in the loft exactly as it does in an airing cupboard.

Frost, heat loss and waiting for hot water

A roof space is outside the insulated envelope of the house. In a cold snap the air up there can drop close to outside temperature, so the cold feed, the valves and any pipe runs need proper insulation, and the cylinder should not sit where the roof insulation has been pulled back to make room for it.

The cylinder also loses heat into a cold space rather than into the house. A modern factory insulated cylinder loses little, but it is worth knowing that heat lost in an airing cupboard at least warms the landing, and heat lost in a loft warms nothing.

Then the pipe runs. If the kitchen is two floors below the loft, the hot water has to travel further before it arrives, so you run more water off before it comes through hot. In a tall house that can be noticeable. Keeping runs short, insulating them, and in some layouts adding a secondary return all help, and all belong in the design before the cylinder goes up.

Access for servicing and leaks

An unvented cylinder should be serviced every year, and the engineer needs to reach the inlet controls, the expansion vessel, the tundish and the immersion with room to work. A pull down ladder, boarded route to the cylinder and a fixed light make that straightforward. Crawling across joists with a torch makes it a job that stops getting done, and that is how safety valves end up untested for years. Our article on what happens in an annual unvented cylinder service covers the visit.

Leaks are the other reason access matters. A cylinder or fitting leaking in an airing cupboard is usually noticed quickly. In a loft it can run for days before it shows as a stain on the ceiling below. A drip tray under the cylinder, piped to somewhere visible or to outside, is a sensible addition on any loft installation.

Will it fit through the hatch?

A standard upright cylinder of a useful size is taller than most people expect, and many loft hatches are small. Measure the hatch opening, the headroom at the spot where the cylinder will stand, and the headroom needed above it to withdraw the immersion heater for replacement.

Where height is the problem, a horizontal cylinder that lies down across the joists is often the answer, and a slimline one can help where the width is tight. Our guide to horizontal and slimline hot water cylinders covers the trade offs of each shape.

What drives the cost of moving a cylinder to the loft

Moving a cylinder is a relocation and a replacement at the same time, and the loft adds work at every stage. The main cost drivers are the platform and any structural work, the new flow and return and hot and cold pipe runs, the discharge route, the electrical supply for the immersion and controls, removing the old cylinder and making good the cupboard it leaves behind. The cylinder itself is rarely the biggest item. Our article on what a cylinder replacement actually costs goes through each driver in turn.

Before committing, compare it with the alternatives: a smaller or slimmer cylinder in the existing cupboard, moving it to a utility room or garage instead, or converting to a combi boiler if the household and the mains supply suit one. Converting to a combi boiler frees the cupboard completely but changes how much hot water you can draw at once.

Getting a loft cylinder surveyed

If you are thinking about putting a cylinder in the loft, or replacing one that is already up there, call 020 4652 5111. We will look at the joists and platform, walk the discharge route, check the incoming main can feed an unvented cylinder, and tell you honestly whether the loft is the right place or whether another position will serve you better. Our unvented cylinder installation page covers how we fit them, and our rates are on the pricing page and agreed before we attend.