Hot water cylinders#

Older cylinders may not be insulated to the modern standard - 80 mm of of hardened foam. Very old cylinders may not have any insulation at all. either way, you can use a cylinder jacket to top it up.

Cylinders are meant to have a thermostat that limits the temperature of the hot water. It is very common to find they don’t work because a wire or the strap that holds them on the tank is broken. If you can’t see a stat, look on the floor.

Community buildings typically have very long pipe runs from the cylinder to the taps. If that means the water cools before it gets to the tap, you might be cranking up the temperature of the cylinder to compensate. It’s best to insulate the pipes you can. Slip-on DIY pipe insulation is cheap. Professional insulation installers have access to better materials and skills to insulate the difficult bits.

For your hot water timings, as long as you are heating the water enough to kill Legionella bacteria, you want to just heat the water you need, without it sitting around to cool for a long time, although new, well-insulated cylinders can hold hot water for up to 48 hours.

Smart controls with a bacteria prevention feature

The standard approach for venues with tanks appears to be running the boiler flow at least 70C, so that the tank will heat to at least 60C, and then if necessary using mixing valves at the taps to reduce the hot water temperature so that no one gets scalded - and then to heat the tank often enough to avoid Legionella.

Some smart controls designed for houses come with a Legionella prevention option, for instance, raising the tank above 60C if the hot water hasn’t been heated for at least two consecutive hours in the last two days. We think that with a condensing modulating boiler, in houses that are insulated, that might mean they can run the boiler flow lower and get the energy efficiency advantages that result - but that relies on the controls being able to raise the boiler flow temperature just for the length of the bacteria prevention cycle, and it’s hard to tell from the description whether this happens. We aren’t competent to comment on when this is suitable in community venues, which often have long pipe runs that could themselves store a fair bit of cooling water. Venues with hot water cylinders should take professional advice about Legionella regardless of whether they are involved in HeatHack. We’re happy to be enlightened if anyone has advice for us about this.