From PassivHaus to AECB Carbonlite, more and more people are making their homes ‘airtight’. Not only does making your home airtight make it incredibly energy efficient, but it can drastically increase the value of your property. But, what if you want to include a traditional log burner in your airtight house? Is it possible? Keep reading and Direct Stoves will tell you everything you need to know.
What is an airtight house?
If you’re unfamiliar with new building methods and technologies such as PassivHaus and MVHR, the idea of creating an airtight home may sound daft, dangerous even!
The reality is quite different however.
The basic principle of an airtight house is to create an air barrier line all the way around the building – including the walls, ceiling and floor.
Under methods such as PassivHaus, a ‘whole building’ approach is taken, where the housebuilder looks to insulate the property as much as possible using:
- Accurate design modelling using the Passive House Planning Package (PHPP).
- Very high levels of insulation.
- Extremely high performance windows with insulated frames and robust construction e.g. high-quality seals.
- Thermal bridge free construction – thermal bridges are areas of a building that have much higher levels of heat transfer than the surrounding parts.
- A mechanical ventilation system which will be able to recover large amounts of heat.
All of these things combine to create a home which strictly regulates the flow of heat in, out and around a building.
So, whilst not technically ‘airtight’, homes with this level of insulation performance have exceptional levels of thermal performance.
What are the different types of airtight home standards?
There are two main standards which define when a house is airtight.
This is a standard which originated in Germany and refers to homes which use very small amounts of energy. To be classed as a PassivHaus a property has to pass very strict building criteria. As such, not every airtight home is a PassivHaus, yet every PassivHaus is an airtight house.
Carbonlite is basically the UK’s version of PassivHaus. Established by the AECB (Association for Environment Conscious Building), Carbonlite sets out the steps required to create and maintain buildings which have extremely low energy use and CO2 emissions.
Can you use a log burner in an airtight house?
So, now that we’ve established exactly what an airtight house is, we arrive at the all important question – can you actually use a log burner in an airtight house?
The answer is yes; but with caveats.
There are several installation requirements which you will need to meet in order for your log burner to function safely.
In the next section, we’ll take a look at each of these installation requirements.
How to install a log burner in an airtight house
As you can imagine, installing a log burner in an airtight house is very different from installing one in a standard house.
This is primarily because of the issue of air permeability.
At present, UK Building Regulations require that homes have a maximum air permeability of 10 m3h-1m-2. This means that standard homes allow in sufficient air for a log burner to operate.
Airtight homes, by their very nature, do not. This means that you have to do several things during installation to ensure that the log burner will function properly.
Below are the key considerations you need to bear in mind in order to properly install a log burner in an airtight home.
Log burner heat output
The heat output of the log burner is an important factor. Why? Because, the higher the heat output, the more oxygen it will require to function.
Thankfully, because airtight homes have such high-thermal efficiency, they don’t require a huge amount of heating.
As such, a PassivHaus or AECB Carbonlite house will generally only require a log burner that has a heat output of between 1 and 3kW.
Of course, this is only a general rule. If you have a particularly large airtight home, then you may require a log burner with a higher heat output.
Other factors such as the aspect of your home, the amount of direct sunlight it gets throughout the day and other sources of heat (e.g. solar panels), will also affect what heat output you require from a log burner.
Combustion air supply
In an airtight home, it’s incredibly important that a log burner has a proper supply of air.
A proper supply of air will not only help the log burner burn properly, but it’ll keep things safe too.
So, in an airtight home, you don’t want the log burner to be drawing its air supply for combustion directly from the room in which it is installed.
Instead, a log burner in an airtight home needs to draw its combustion air supply from fresh air outside of the home. This should be done via a pipe or tube that is connected directly to the log burner body, which passes through an external wall to the air outside.
This is known as direct air supply (or external air).
It’s important to note that not all log burners can accommodate a direct air supply. So, if you’re buying a new log burner for your airtight home, be sure to buy one that is direct air supply (or external air) compatible.
You can view Direct Stoves’ range of log burners which are direct air supply compatible here.
DIBt tested log burners
Another thing you need to look for when selecting a log burner for your airtight home is whether or not it has been subjected to the DIBt test.
The DIBt test was developed in Germany and has been designed to test the effectiveness of a log burner’s room seal – particularly the airtightness of the log burner door.
A log burner which passes the DIBt test will be able to handle any air pressure changes that may occur as a result of the use of MVHR (Mechanical Ventilation Heat Recovery) technology in a property.
DIBt tested log burners will also feature a direct air supply, which makes them effectively 100% room sealed.
Note – it’s not essential that you buy a log burner which has been DIBt tested, (it’s the direct air supply that’s most important), it’s a big thing to look for if your airtight home will be using MVHR technology.
If you’re in the process of building your airtight home, then at some point just prior to completion it’s likely that you’ll have to subject your property to a pressure test.
Depending on where you live, your local authority building control department may insist that your log burner is installed prior to the pressure test being carried out.
The pressure test will involve blocking off all ‘holes’ in the skin of the building, including the direct air supply to the log burner.
Occasionally, however, the direct air supply will not be blocked off for the test. This will lead to a small amount of air leakage from the log burner, but this is not generally considered an issue in ensuring that your home is classed as ‘airtight’.
Note – the main takeaway here, is that you should check with your local building control department whether or not they will expect your log burner to be installed prior to a pressure test being carried out.
Mechanical Ventilation Heat Recovery (MVHR)
MVHR is a technology that involves mechanically blowing air into a property through heat exchangers. MVHR is used to provide fresh air into a building, whilst retaining the energy that has already been used in heating the building.
It’s because of this that MVHR is often used on airtight homes and other new builds.
However, MVHR technology can have an impact on the air pressure in a building. In some instances, it can lead to the creation of negative pressure in a room – something which would impair the function of a log burner.
If you do intend to use MVHR technology in your airtight home, then it’s essential that you use a log burner with a direct air supply. This means that regardless of the air pressure in a room, the log burner will still be able to function properly as it is drawing it’s air supply from outside the property. It is also useful to use a DIBt tested log burner if you think the MVHR will have a major impact on your property’s internal air pressure.
At present the Building Regulations stipulate that solid fuel burning appliances (such as log burners) require the installation of a non-closable air vent in an external wall of the room in which they are situated.
As you can imagine, adding a non-closable vent in an external wall would prevent a home from being airtight.
To get around this problem, and recognising that increasing numbers of airtight homes are being built, some changes have been made to the relevant standard – BS 8303.
According to HETAS, the UK-body that oversees regulations for log burner installations, the revised BS 8303 allows for log burners to be installed in airtight homes, without a non-closable air vent, provided that:
- “The log burner is installed with a dedicated external air supply kit, which is completed in-line with the manufacturer’s instructions, including consideration for the duct diameter, total length, air inlet terminal position and duct material specification.
- Appropriate risk assessment and commissioning procedures are undertaken to understand the property’s current ventilation and air tightness.
- Appropriate smoke tests are completed, including with any extract running and spillage tests when the door of the log burner is opened for refuel”.
Most local authority planning departments will also want to see that the log burner installation and the steps above have been carried out and signed off by a HETAS-qualified installer.
Note – the key takeaway here, is that it’s possible to install a log burner in an airtight home without adding non-closable air vents, provided the installation meets the requirements of BS 8303.
Carbon monoxide detector
You will also need to ensure that you have purchased a carbon monoxide detector to place in the room where the log burner will be installed.
Even though the log burner will be using a direct air supply and venting smoke and combustibles outside, you will be required to have a carbon monoxide detector in place at all times.
HETAS qualified installation
As you’ve probably picked up by now, a key theme running through all of these points is the importance of correctly installing a log burner in an airtight home.
Not only do you need to ensure that you buy the correct size log burner, with a direct air supply, but it also needs to be installed in a way which takes into account any MVHR technology in place as well as the stipulations of BS 8303.
That’s a lot to take into account and get right!
So, we’d strongly recommend that you always use a HETAS-qualified installer to install a log burner in an airtight home (many local authorities will insist that you use one anway).
HETAS installers are fully trained in the correct installation procedures for log burners in airtight homes and can do so in a way which will ensure your local planning officers will be kept happy.
To find your nearest HETAS-qualified log burner installer, use HETAS’ portal here.
The best log burners for airtight houses
Here at Direct Stoves we stock a massive range of log burners from all leading brands. As such, we have a large selection of log burners that are direct air/external air compatible.
Below we’ve highlighted a few of our most popular log burners that are direct air/external air compatible.
Note – if you are keen to check if a particular log burner has been DIBt tested, you will need to confirm this directly with the manufacturer.
Hamlet Solution 4 DEFRA-Approved Stove
The Hamlet Solution 4 is a highly-compact log burner, ideal for airtight homes where large volumes of heat output are not required.
Featuring a multifuel function, the Hamlet Solution 4 can not only burn seasoned wood, but also solid smokeless fuel too.
What’s more, the Hamlet Solution 4 comes with a 10-year warranty, is clearSkies rated for its low particulates and emissions and is DEFRA-approved, so it can be used in smoke control areas.
As you would expect from it being on this list, it is also external air compatible, with an external air kit available at an additional charge.
Woolly Mammoth 5 Widescreen Wood Burning Stove
The Woolly Mammoth 5 is a real ‘statement’ log burner thanks to its widescreen viewing window and sleek contemporary looks.
It’ll really look the part in your eco-friendly home. But it’s not just looks. The Woolly Mammoth 5 has some serious green-credentials too. Being EcoDesign ready, it burns exceptionally cleanly giving off minimal particulates and emissions.
It also features adjustable primary and secondary air intakes which work harmoniously with a pre-adjusted tertiary air supply to produce highly efficient combustion, reducing unnecessary refuelling and running costs.
Hunter Herald Allure 04 Wood Burning Stove
A neat, compact, yet powerful little stove, the Hunter Herald Allure will make a fantastic all-round log burner for your airtight home.
The Hunter Herald Allure is packed with features such as airwash, primary, secondary and tertiary air intakes and a whopping 81% efficiency. All of these features combine to create a log burner which will not only keep your fuel bills down, but which is environmentally friendly too.
If you want to elevate the Hunter Herald Allure so that it becomes a centrepiece of your living room, then there’s an optional stove bench which can provide a platform on which the log burner can sit. Pick from two stove bench sizes; 800mm and 1195mm.
To ensure that this log burner is suitable for your airtight home, make sure you add the optional direct air kit to your purchase.
Portway Luxima Wood Burning/Multifuel Stove
With a history that can be traced all the way back to the 1800s, Portway has a long-established reputation for building high-quality, innovative log burners.
The Luxima is no exception.
Portway stoves are noted for their efficiency. They are designed to maximise the length of a burn, meaning you’ll get a lot of prolonged heat from your firewood.
The Portway Luxima takes this approach to efficiency to the next level with a quaternary air supply, which not only means the Luxima burns with incredible efficiency, but can also be controlled with a high-degree of accuracy.
That’s not all. The Luxima also features a slim-depth design – which means it will take up minimal space in your home.
With a 10-year guarantee, this is a log burner which is quite literally guaranteed to give you years of reliable service.
Find a log burner for your airtight home here
As you can see, there’s many things that go into installing a log burner into an airtight home. But, as any long-term log burner user will tell you, the result is more than worth the effort!
If you’re going to be including a log burner in your airtight home, then explore our complete range of direct air compatible stoves here at Direct Stoves. The models listed above are just the tip of the iceberg!
Shop direct air compatible stoves at Direct Stoves now
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