Wood Fired Boiler Cooker – Installation Guide
Wood Fired Boiler Cooke Pipe positions: see the following pdf documents:
The pipes are 28mm copper and a Ladomat21 or equivalent must be used. These boilers can only be used with a sealed system if an external overheat ‘dump’ system is used as well. If in doubt or you want advice on you proposed system email email@example.com with diagrams, pictures etc.
Best Linked, multi-fuel source heating and hot water system.
One of the first differences to grasp between a gas/oil/pellet boiler and a log wood burner is that you cannot turn a log wood burner off, so you cannot rely on electricity alone to extract the energy from the boiler. What would happen in the event of a power failure? Where would the energy go? To this end in the UK we have always used open vented systems, so the system is open to atmosphere and the boiler cannot over pressurize. In Europe, and starting to in this country, they tend to use sealed systems, then add a safety dumping system that floods the boiler with cold water in the event of an overheat. You can do this with a Thornhill Range cooker/boiler, but I always prefer the simpler system, and you still have mains pressure hot water even though the primary water is open to atmosphere.
So here is a diagram of the basic system Thermal Store-Vented.
It looks complicated, but it isn’t and is easily understood if we break it down into its constituent circuit diagrams.
Diagram 1 – Thermal-Store-Boiler-circuits
This diagram shows the thermal store, in reality a large insulated water tank. Energy (heated water) from the log wood boiler circulates under gravity, allowing the water to flow through the boiler at its own pace. There is an electric booster pump which comes on occasionally when the amount of wood being burnt is too high for natural gravity circulation. Using natural circulation like this is always best with a log wood boiler, but does require the bottom of the thermal store to be a minimum 600mm above the boiler, ideally on the first floor where hot water cylinders were traditionally sited in the UK.
If this cannot be done in your instance please contact me via email and we can discuss your scenario separately.
You can also connect one or more other boilers to the thermal store. If they are oil, gas or pellet they can be sighted anywhere and the energy pumped to the store in 22mm diameter pipe work. The flow is to the top of the store and the return cold and the bottom. Electrically this is wired up via a thermostat sited in the middle of the store. This stops the second boiler firing if the water in the store is warm, i.e. it’s full of energy, but if in the morning it’s too cool, or if you are ill, or on holiday, the oil/gas boiler will automatically fire to top-up the store, to warm your house and/or give you hot water. A second thermostat is also sighted in the middle of the store. This is set around 85C and if the water in the store gets above this, it automatically turns the central heating pump on to take some energy out.
Diagram 2 – Thermal Store – Hot Water Circuit.
Built inside the thermal store is a 12 meter long coil of finned copper. Water at main pressure is fed in the bottom and out comes hot water at main pressure – perfect for showers. Now the water inside the thermal store might be at 90C, which would be somewhat dangerous if the water came out at that temperature, so to control the temperature of your hot water, a simple mechanical thermostatic valve is used (the same as is used on shower units) and this bleeds in mains pressure cold water to mix the water to the set temperature usually around 55C. All this is built into the thermal stores we supply and sell.
Diagram 3 – Central heating Diagram
Hot primary water (the water inside the thermal store, not the hot water you use) is simply pumped round the radiators or underfloor heating via a pump. The outlet for the central heating is about halfway down the store so the water at the top of the store is always hotter to generate your hot water.
The central heating pump is controlled via a clock and room thermostat in the normal way.
Diagram 4 – Thermal-Store-Solar-circuit
This shows the solar hot water circuit. The only reason you have a separate coil for the solar water is that it has to contain antifreeze because the panels are outside all winter. A smaller finned copper coil is used to transmit the energy from the panel to the thermal store. Our kits come with a pump/control unit and are reasonably priced and simple to install. The control unit has two temperature sensors. One is placed up on the solar panel and one is placed at the bottom of the thermal store. When the water in the panel is 10 degrees C more than the water at the bottom of the store, the control unit turns the pump on and the heat flows from the panels to the cylinder. If the temperature difference drops to 5C then the pump is switched off. All very simple and reliable. It is another reason to have the thermal store on the first floor as the run for the flow and return from the solar panel to the cylinder is mainly in the loft with two pipes running down in the airing cupboard.
Now if you look back at Diagram 1 (Thermal Store-Vented) you can see all the different circuits and it should all make sense.
Advantages and disadvantages of thermal store systems.
You could just connect your Thornhill Range Cooker/boiler to a hot water cylinder and set of radiators. This would save money on the capital outlay, but would not be as good a system or as efficient and convenient.
- Main pressure hot water. No need for shower pumps.
- Hot water is not stored, so is fresh and can be used for cooking, and there is no risk of Legionnaires’ disease. (Also if you buy your store from us it is made of copper which is also safer against Legionnaires’ disease and other water-borne bugs.)
- The thermal store allows you to store more solar energy in the summer. If you just have a coil at the bottom of a standard cylinder, you have to shut the solar pump off, when the water temperature gets to 55C to prevent scalding. With a thermal store you can heat more water up to 90C and thus store more energy.
- In a similar manner the store smoothes out the inevitable fluctuation in the output of the wood boiler. The energy will fluctuate as new logs are added and then the fire burns down between reloads of fuel.
- Second or third boilers can be added very simply. A gas or oil boiler will give you heating if you’re ill, or keep the house warm if you’re away in winter. Instead of trying to be 100% ‘green’, settle for 80% and all the convenience and back up. The oil or gas boiler is the cheapest, simplest, most reliant standard boiler, not a system or combi boiler, and should cost under £1,000.
- Electric immersion heaters can be added for a further back-up and choice of fuel. You’re now not tied to one fuel source, and if you have electric photo voltaic panels, any spare energy can be directed to the thermal store.
- You can add the solar later (as long as you buy the store with a coil in it, £65 extra) at any time, and you can add a second boiler later if you didn’t want to do it in one. We always add the fitting to connect at least one boiler and if you ask we can add fitting for a third boiler.
- Slightly higher capital outlay. The stores cost between £1,000 and £1,500, though – they are at only 5% VAT and this includes the solar coil and there is probably quite a saving in valves and fitting costs as they are so simple to fit.
- In very, very hard water areas you can chalk up the hot water heat exchanger. Either a water softener can be fitted (around £500) to just the hot water side or the coil can be flushed out every 10-15 years. It’s not a huge problem.
- Like a combi boiler or unvented hot water cylinder, the amount of hot water generated has a maximum of the amount of water flowing to your house, so you must check your flow rate and it needs to be above 17 litres a minute. Contact me direct if you have problems with flow or a large multi bathroom property. firstname.lastname@example.org
- Like a combi boiler there is also a maximum amount of hot water flow. Enough for two showers at a time if you have the flow and pressure to your house. Baths can be filled, usually one at a time but you can fill baths all day as all the energy from the boiler is used efficiently.