Have you got a roaring fire in your living room, putting out way more heat than you need? Why not use some of the extra heat for your hot water system?
What’s a wetback?
A wetback is essentially a series of tubes built into your fireplace that allow you to heat water by pumping it through the tubes.
They’re usually used in smaller homes for systems with a low heating requirement. They’re often installed as siphonic systems, meaning that they operate without a pump – they rely on the hot water to naturally rise in the system and create a fluid flow through HWC and back to the wetback.
Another option is to connect a radiator to the wetback circuit. This allows you to move some of the heat output from the fireplace to another room, which makes the fireplace more versatile.
One challenge with wetbacks is that there’s minimal control over the heat source. A gas or diesel boiler can be switched on and off electronically, providing good control over the heat. A wetback can’t, so it’s best for small systems where some over- or under-heating isn’t such an issue.
Limitations
Wetbacks typically have a low heat output, because much of the heat from the fire goes into the room rather than the water. As a guide, you might get 4-5 kilowatts out of the wetback. This is enough for one (maybe two!) radiators, or a connection to your hot water cylinder.
But it’s not enough to heat your whole house. By contrast, a gas or diesel boiler would easily 20 kilowatts.
Wetback definitely have their uses, and if you have a small home and you’d like to cut down your hot water bill, it’s worth looking into.
If you’re trying to keep your whole house warm all winter then it’s probably not sufficient for the task.