Unvented Cylinder Installation Sevenoaks

Sevenoaks and the villages around it run to larger, often older detached houses with two or three bathrooms, and that is precisely the situation an unvented cylinder exists for. It delivers mains pressure hot water to every outlet at once, which a combi cannot do and a gravity fed vented system does badly the higher up the house you go.

What decides whether it works is sizing and pipework rather than the cylinder itself, and in a big house the problem is rarely a shortage of hot water. We are a Gas Safe registered and OFTEC certified business based in Bearsted, covering Sevenoaks and the TN13 to TN15 villages out towards Otford, Kemsing and Riverhead. Below is what actually matters when one goes in.

Why these houses suit one

An unvented cylinder is sealed and fed straight from the mains, so it passes mains pressure through to every tap rather than relying on the height of a tank in the loft. In a three storey house that difference is dramatic, because a gravity system has almost no head left by the time it reaches the top floor, which is the whole argument for going unvented in a tall building.

The other reason these houses suit one is simultaneous demand. Two showers and a basin running at eight in the morning is the test that separates stored hot water from heated on demand, and a cylinder passes it because the water was heated in advance rather than as it travels.

Sizing it properly

The number people fixate on is litres, and it is only half the answer. A cylinder is a battery, so what matters is how much it holds and how fast it fills back up. A smaller cylinder with a generous coil and a boiler that can drive it will often outperform a larger one that takes half the morning to recover, and it takes up less of the airing cupboard while doing it.

The sizing conversation tends to go wrong in the same way. People count bathrooms rather than simultaneous use, and they count bedrooms rather than the people actually in them. A five bedroom house where two adults live has quite different demand from the same house with four teenagers, and no rule of thumb based on room count catches that.

The far bathroom, which is the real complaint

In a large house the complaint is seldom that the hot water ran out. It is that the bathroom at the far end takes an age to run hot, and the answer often offered is a bigger cylinder. It usually is not.

In a large Sevenoaks house the fix is usually a secondary return rather than a bigger cylinder, because the complaint is how long the far bathroom takes to run hot rather than how much hot water there is, and extra storage does nothing about distance.

A secondary return is a small loop that keeps hot water moving from the cylinder out towards the far end of the house and back again, driven by a modest pump. The water in the run never gets the chance to go cold, so the tap runs hot almost immediately instead of after a bucket has gone down the drain. On a long horizontal run in an older house it transforms how the place feels to live in, and it costs a fraction of a larger cylinder.

It is not free to run, since something is circulating water and losing a little heat while it does. Putting it on a timer so it runs at the times the household actually uses hot water, rather than continuously, is the sensible middle ground and it is worth insulating the loop properly while the pipework is accessible.

What the installation involves

Fitting an unvented cylinder is notifiable work under the building regulations. It has to be carried out by somebody who holds a qualification for unvented systems, which is separate from Gas Safe registration, and then notified to building control, so it is fair to ask whoever quotes to show you that certificate. The safety kit, the expansion vessel, the relief valves, the tundish and the discharge pipe, is what the regulation is about, and where that discharge can physically run is the constraint most likely to change where the cylinder ends up.

The incoming mains gets measured before anything is ordered. A cylinder can only ever pass on the water arriving at the property, and some of the older houses out towards the villages still run on a narrow or shared supply that was adequate for one bathroom and is not for three. Upgrading that is sometimes part of the job, which is why a hot water cylinder is quoted after a visit rather than over the phone.

Coming off a vented system

In an older house this is often a conversion rather than a new install, and that is a bigger job than swapping one cylinder for another. The cold tank and the feed and expansion tank come out of the loft, the old vent pipe goes, and the distribution pipework is worth assessing while everything is open.

Worth correcting a common assumption there. Old gravity systems were plumbed in generous bore precisely because gravity needed it, so the pipe size itself is rarely the problem when you go to mains pressure. What can be a problem is its condition, because decades of scale narrow the bore from the inside, and so can the length of the runs in a big house. Assessing it while the floors are already up costs very little. Revisiting it afterwards does not.

The compensation is that a loft comes back. In our experience, an unvented cylinder works better than a vented one wherever a loft conversion is on the cards, because a vented system needs its cold water tank up there and relies on gravity from it, while a sealed unvented cylinder needs no loft tank at all, a point Viessmann's guide to vented and unvented cylinders makes as well. In a house where that space is worth converting, removing the tanks is often the quiet reason the whole project makes sense.

Keeping it right afterwards

An unvented cylinder needs an annual check, which is not the same thing as a boiler service although the two are sensibly done in one visit. The expansion vessel loses its charge over time, the relief valves want testing, and hard water scales the coil here as it does everywhere in Kent. Skipping it is how a dripping tundish becomes the first anyone knows about it.

It is also usually a warranty condition, so the record is worth keeping. The early signs a cylinder is going show up at an annual check long before they show up as a problem in the house.

So, size it on simultaneous demand and recovery rather than litres alone, measure the mains before ordering anything, and if the complaint is the far bathroom look at a secondary return before a bigger cylinder. CTL Plumbing & Heating covers Sevenoaks and the TN13 to TN15 villages from Bearsted, with free home visits and free quotes across Kent. To talk one through, get in touch.