Help designing a wood burner heating system

15 Nov 2006
Reaction score
United Kingdom
I have a Villager kitchenia make of wood burner with back boiler heat output of I think only 9000BTU

I currently have no loft, cylinder or roof cold water tank.

I want to fit something like a twin coil cylinder with the bottom coil for later use when connected to solar panels.

The twin coil cylinder can be fitted in the room above the wood burner.

The main bedroom has 1 radiator and the size is 200cm x 40cm (ish)

The guest bedroom has 1 radiator and the size is 100cm x 60cm (ish)

The bathroom is downstairs and there is a towel rail and the size is 100cm x 40cm

The lounge / dining room is downstairs and there is 1 radiator in the dining room and the size is 150cm x 70mm (ish)

Should I have an unvented twin coil cylinder with correct coil for a wood burner, or a vented twin coil cylinder with the correct coil for a wood burner or consider a thermal store?

Some comments from others include:

Unvented cylinders may be allowed as Newark manufacturers of unvented cylinders have confirmed this. IE: the unvented going on a
wood burner this would have to be checked over by building control before installation as a wood burner would be classed as an un controllable device.

Also a friend had this to say: I have spoken to John at Oso cylinders who we normally use for our twin coil unvented cylinders. He has said that you could only use their cylinder for a woodburning or soild fuel back boiler if you have some way of controlling the temp of the water coming from the back boiler. The problem being the over heating of the cylinder.
He assures me all the other manufactures of unvented twin coil cylinders will tell us the same. If the back boiler currently has no temperature control he said it maybe worth talking to the manufacture of the back boiler to see if they can suggest anyway around it.
Sponsored Links
midknight said:
I want to fit something like a twin coil cylinder with the bottom coil for later use when connected to solar panels.

I think the manufacturers' instructions say something vague, like you can only use an unvented cylinder for solid fuel if additional, unspecified safety devices are installed.

IMHO, the main problem is that you can't use the unvented cylinder for a heat sink for the wood burner, because the statutory safety devices are intended to isolate it from the heating system if it starts to overheat. The 2-port valve supplied must be fitted; this will spring-return shut if the power fails, leaving no means of dissipating the heat from the wood burner.

The BBA certification requires all the safety devices to be installed, and it would be a very brave or very incompetent technician who omitted them.
You see quite a few 2-port valves in unvented system OEM's packaging on E-Bay; draw your own conclusions.

In reality, unvented cylinders are greatly over-rated, their only advantage (in the UK) is in flats or in supplying a shower without requiring a pump. You can achieve adequate flows to appliances from a loft tank, if the system design is done competently. Loft tanks in colder climates are less practical. I'd recommend sticking with vented hot water storage.

If you really, really wanted a second, unvented cylinder you could heat it with a secondary pump off the primary flow, with the flow & return tees closely spaced on the same pipe. If the pump didn't run, there'd be no flow to the unvented system; the pump would be interlocked with the unvented safety devices.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links