Ever since the discovery and taming of fire, humans have been heating their homes with wood. During the Victorian period, coal became the fuel of choice and then in the last century until the present day, the preference has been for gas. Nonetheless, there are many properties not connected to a mains gas line, which have to use heating oil or LPG. Switching from these types of fuel to a wood-fired boiler could not only put a renewable resource to good use, but also reduce your heating bills and carbon emissions.
This article is going to look at biomass boilers, particularly wood-fired ones. It will compare some different forms of heating systems and also explain why wood is such a great fuel in comparison to fossil fuels. It will not be covering cosy-looking wood-burning stoves, however; you can see my article on those by following the link below. This is about those big ole’ burners that are used as a main boiler.
Wood burning stoves: http://www.energysavingwarehouse.co.uk/news/166/20/Burn-Baby-Burn-A-Quick-Look-at-Wood-Burning-Stoves.html
What are wood burning boilers?
Basically, a wood fired boiler is one that uses burning wood to heat hot water and power the heating system. This is usually because the house is not attached to a main gas line, perhaps due to location. Almost every home in the UK has a boiler of some description for this purpose, the most common being gas-fired. The biggest difference in using these types of boilers is that the fuel has to be loaded into the boiler by the homeowner and isn’t ‘on tap’ like gas. Apart from that they work in pretty much the same way as any other boiler.
Some examples of HDG pellet boilers
The Energy Saving Trust estimate that compared to an oil burner, a wood (pellet) burner will save you around 30% per year on fuel bills [1], and even more if switching from liquefied petroleum gas (LPG). However, there are even more reasons for switching to wood.
Why wood?
First: wood is a renewable resource, meaning that as long as we plant a new tree for every one we cut down, it shouldn’t run out. As such it’s easy to manage and this article assumes that any wood consumers are using a sustainable supplier. Currently in the UK we are growing more wood than we are using, which is good, although we are also importing a lot too; which is not so good. As I’m sure we are all painfully aware, fossil fuels (coal, oil and gas) are running low and the price of using them is ever increasing. Wood, being renewable, doesn’t seem to be suffering from this affliction and the prices are remaining pretty stable, meaning that switching to wood will reap instant rewards.
Second: wood is carbon neutral. Now; a few people recently have raised an eco-eyebrow when it’s mentioned that burning wood is carbon neutral, so here’s an explanation of why this is so: A tree will absorb exactly the same amount of carbon while growing as it releases when it is burned; this is called a closed carbon cycle. With many modern wood-fired boilers working at well over 90 percent efficiency, there is also little in the way of other emissions as well. This is totally different to an open fire where 80 percent of the heat goes up the chimney along with large amounts of smoke.
When dealing with wood we must also remember that it works on a much shorter cycle than fossil fuels. When fossil fuels are burned they release carbon that has been stored up underground over million of years, hence the massive extra amounts that are currently being released into the atmosphere. Wood, however, is recycling carbon that has been removed over the last few years – say 10’s of years at the most – thus maintaining a reasonably healthy carbon balance. Plus, the ash can then be used as a garden fertilizer; zero carbon, zero waste.
Different types of wood
If using a biomass boiler, there are many different fuels you can use, wood being just one of them. However, it’s wood boilers under discussion here, so, in terms of the different types of wood available, there are three main ones: logs, chips and pellets.
Some boilers can use all three types, whereas some are designed to use only one. It’s worth looking into the type of fuel you would wish to use before you choose your boiler. Here’s a quick round up:
Logs – What can I say? They’re logs, they burn. Logs are the heaviest to transport and quite bulky to store, but you may have a lot of trees within your property that need maintaining, thus giving you an ample supply of logs. Alternatively, you may be lucky like a friend of mine whose brother is a tree surgeon and keeps him stocked up with an ample supply of cut logs.
Wood chips – These are simply wood that has been chipped in the machines you see tree surgeons using. If you are canny enough you can get them for free by simply asking for some, but probably not in the quantities a boiler would require. They are easier to transport and store than logs, but will also need seasoning for maximum combustibility. They’re also relatively cheap.
Wood pellets These are my personal favourite of the bunch and would be my fuel of choice for a wood boiler. They are made from waste sawdust that is compressed and sealed using the natural lignin present in the wood. They have a low moisture content, high energy density, excellent heat output, low ash and are easy to store and handle. They are the most expensive to buy, but also the most efficient burners, which equals things out somewhat.
On the subject of pellets; I recently bought some ecologs for my fire, which are essentially log-sized wood pellets. I have to say they are by far the best fuel I have ever burned. They burn very hot and for a very long time. If pellets perform to the same standard then I can highly recommend them. Oh yes, and before you say it, I know it’s not very green having and open fire; but nobody’s perfect. If you do have a log burning stove why not consider a ‘Chimney Pillow‘ to reduce draughts and keep heat within the room?
The costs
The costs of installing a wood burner and how much it may save you in energy, carbon and money are covered below:
Typical boiler costs:
| Boiler Type | Estimated Cost |
| Condensing Gas or LPG Boiler | £500 to £600 |
| Condensing Oil Boiler | £1000 to £1100 |
| Solid Fuel (Coal) Boiler | £1400 |
| Coal or Wood Stove with back boiler to run 10 radiators | £600-£700 |
| Pellet Stove (without back boiler) | £1500 |
| Log/Pellet Boiler | £3500 |
In addition there is the cost of the flue and installation-typically in the range of £1000 to £1500 plus VAT depending on the type of heating system installed. There will also be the cost of fuel storage to consider.
Source: National Energy Foundation [2]
Typical fuel prices:
| Fuel Type | Price per unit | kWh per unit | Pence per kWh |
| Wood chips | £80 per tonne | 3,500 kWh/t | 2.3p/kWh |
| Wood pellets | £185 per tonne | 4,800 kWh/t | 3.9p/kWh |
| Natural gas | 3.9p/kWh | 1 | 3.9p/kWh |
| Heating oil | 63p per litre | 10 kWh/litre | 6.3p/kWh |
| LPG (bulk) | 52p per litre | 6.6 kWh/litre | 7.9p/kWh |
| Electricity | 13.0p/kWh | 1 | 13.0p/kWh |
Source: The Biomass Energy Centre [3]
As can be seen from the above, wood burners are expensive to install. However, they are the cheapest to run and result in less carbon emissions than other forms of boiler.
The savings
If switching from oil to wood, the savings would be £365 in bills and 4500kg carbon emissions per year. If switching from LPG, the savings would be £608 in bills and 3478kg carbon emissions per year. This assumes a UK average gas consumption of 16,000kWh per year [4] and that 95 percent of this energy is for space and water heating – only 5 percent is used for cooking.
Don’t forget that you can also make use of the renewable heat incentive (RHI) [6] where you will get up to 9 pence per kWh of energy you generate, depending on the size of boiler you install (an how well the RHI holds up under the spending review!).
Some other things to consider
If you already have an oil or LPG boiler and are considering switching to wood, or if you are going to install one in a new home, there are a number of factors to think about first:
- One of the issues of heating your home or business with wood is storage. As an example, a 5 tonne pellet storage tank will require approximately 3m x 3m x 2.3m, and will be filled up by a blower lorry. Obviously you’ll want the biggest tank you have space for, but smaller tanks are feasible. These would probably have to be filled by hand though.
- Another factor to consider is whether it would be convenient for you to load the boiler yourself or would want an all singing, all dancing model that has a large hopper attached to it that will supply the boiler as needed, constantly monitor and manage the temperature and make you a cup of tea in the morning. Remember when choosing your model – you get what you pay for.
- It’s relatively easy to convert an old coal-fired burner to run off wood pellets and conversion kits are available. In some cases you may simply need to make some alterations to the fuel feed supply. Note: Do get this confirmed by an expert before you go chucking wood into a coal burner as I don’t want be responsible for you setting fire to your house.
- ALWAYS buy fuel in bulk whenever you can. It will save time and money.
In summary then…
All the time that timber is being used as a building material and we are buying wooden furniture, there will be an ample supply of waste wood and sawdust. Wood is a far more environmentally friendly way to heat a house compared with any of the fossil fuels. It is a lot cheaper, a renewable resource and often utilises what would normally be a waste product.
If you are in the market for a big ole’ burner, do have a good look at what’s on offer and then embrace your caveman roots; heat your home with wood. Nice.
References
[2] http://www.nef.org.uk/logpile/pellets/cost.htm
[3] http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,59188&_dad=portal&_schema=PORTAL
[4] http://www.carbonindependent.org/sources_home_energy.htm
