Running 2 boilers on a wood fired heating system

[dave28]

Currently using a 14kw Hunter stove with back boiler to heat 6 radiators and would like to add more plus get some automation by adding a second boiler, probably oil or electric, to the system.

I've been told I'll need a Dunsley neutraliser or thermal store to make it work safely.

Anyone on here know anything about them? I'd appreciate any advice.

Thanks.

[Breezeblock]

weve got a 40kw linked into the central heating and it can run alongside our 8kw boiler stove but we have pretty much not used the small boiler as the bigger one is more efficient but they work no bother as the 40 kw boiler runs thru a thermal store

[Pumpy]

woodburner boilers are usually fitted to gravity fed open vented systems, (so you have a cold water tank, feeding a hot water tank with a coil utilized by the boiler, and a system header/feeder tank to feed the gravity/pumped CH circuit,) putting two boilers into one circuit is usually against manufacturers instructions, because depending how the pipework runs it is possible to get HW "cycling" through the other boiler/gravity circuit, or too much heat building up in one part of the system, or other unwanted hydraulic interaction between the two systems when a pump comes on for example, best case it can prevent the system working properly, worst case is damage to the boiler or possibly a boiler explosion.

 

When they talk about a "thermal store" they're usually talking about a hot water tank (HWT), in a single boiler system the HWT is usually fed by the gravity circuit going through the coil in the HWT, one way to add another boiler is to have a completely separate system with it's own system header tank for the additional boiler, but a second coil in the HWT, so may mean adding a coil to the existing tank (not always possible) or getting another tank with two coils fitted. This would fill the requirement for a "thermal store" and keep to the manufactures spec.

 

A Dunsley neutraliser is just a big old manifold, where the cold feed and open vent for both boilers are connected, to eliminate any possible hydraulic interaction between the two boilers/systems.

 

There's some diagrams on the Dunsley website follow the links on the page. More diagrams can be found in the Dunsley neutraliser installation instructions, linked on the Dunsley download page

 

HTH

[treedave]

Yep, got Dunsley type C under the HWT, fed by the woodburner. Got an oil boiler on the other side of the system. When the fire is on and the water is up to temp, thermostat cuts out oil boiler aka saves money. In the mornings the boiler does the HW, no need for a fire, if the evenings get nippy - small fire and switch on the central heating pump, again no oil burnt.

Its good to get a plumber & sparky that have experience with the kit, saves their time / your money as they work out the unusual but simple set up. Get them to talk you through setting the various thermostats and the relationships between them then you can tweek the temps at which stuff cuts off.

Mines saved me 1-2 fills of a 3000 L oil tank per year, but the woodshed has had to double to cope with demand.

[mrstumpy]

I have the same solid fuel burner as you, it is linked to my oil fired boiler using an H2 panel. I have hot water from the immersion and central heating both powered by the wood burner.

The H2 panel has heat leak build in for power cuts and turns off the oil boiler when the solid burner is lit it can also incorporate solar heater if you wish.

 

I have no problems with it and there are several more installations locally which have very warm and happy owners!!

 

The system can be found here: H2 control system

[htb]

Recommend the H2 Panel, very good product and helpfull back up

[dave28]

Many thanks for all this info.

It's amazing how much knowledge there is on A.T

The thermal store is going to be too big for me but I will definitely be looking into the H2 and Dunsley.

Cheers

[Fencing]

Chelmer heating do an ecocat thing its on their website