stovesonline telephone contact logo 0845 226 5754

Stoves for Airtight Houses

New-build houses are becoming increasingly well-insulated and therefore more air tight. This is topical when it comes to installing a woodburning stove or solid fuel stove in an airtight or passiv house.

Here are some examples of standards in building highly insulated airtight homes. Buildings which meet these standards will be warm in winter, cool in summer, and be cheaper to run.


The Passiv Haus

Passiv Haus is a German standard relating to the energy consumption of the building. Passiv Haus (or Passive House) is often used as a wide term to describe low energy buildings, but that is really an inappropriate use for the term. To be a passiv haus, strict criteria must be met regarding energy performance.

Carbonlite

AECB's Carbonlite standard - they are a sort of UK passiv haus equivalent. The standards are expressed in terms of energy use and CO2 emissions per square metre and year - measured in kWh and tonnes respectively.

UK Code for Sustainable Homes

The government's Code for Sustainable Homes. A New-build has to meet the minimum requirements of Code 3, Code 6 being the highest. The Code for Sustainable Homes is environmentally aware and covers a broader range of categories than the others above - standards of material sustainability, water recycling, bike access, biomass heating, pollution are all included.


How do these air tight standards affect the installation of solid fuel stoves and flues?

Stove sizing

One of the main differences between an airtight or passiv house and a 'normal' house is the heat requirement. A highly insulated, new-build house built to Code 6 standards may only need 1-3kW of space heating input in the coldest seasons.

This of course depends on the size of the building, location, aspect etc. For visual impact a larger looking wood burning stove may be required, but the kw output will need to be low. If you have a 10kW solid fuel stove, and you only put 2kW worth of wood in it, you will only get 2kW out. It is however better to have a smaller stove burning harder, than a high kw output stove that you have to 'slow burn'. There are large size woodburning stoves that have good controllability and give a wide range of heat output, ideal for air tight, well insulated houses.

Combustion air

Another consideration is the ventilation requirement for the woodburning stove. Building Regs stipulate that 'Combustion appliances shall be so installed that there is an adequate supply of air to them for combustion, to prevent overheating and for the efficient working of any flue' - Requirements J1, Approved Document J.

This means that instead of the solid fuel stove drawing the combustion air from the room, it ideally needs to have an air supply duct drawing fresh air from the outside connected to the body of the stove itself. Not all stoves have this option; here is a list of stoves that take a direct air supply.

You may wish to talk to us about whether you need partial, total, or 100% direct air for your woodburning stove. If it is a very air tight house, or even an extension to an existing house, built to passive house standard or similar, look at 100% direct air stoves.

MVHR

Mechanical Heat Recovery and Ventilation is very often used in new build houses. This essentially involves mechanically blowing air into the house through heat exchangers. This means that you can slightly over-pressurise the stove room, so that when you open the door of the stove to reload, you should not get smoke coming into the room. An MVHR system may, for example, supply 12000mm2 of vent free area into the stove room. This would in theory be enough to supply a 21kW stove with all it's combustion air requirement.

To use a stove in a property with MVHR, there must not be a negative pressure in the room that the stove is to be installed. A stove with total direct air must be installed, these stoves take all of the air required for combustion from the outside. We do however recommend consulting the HETAS installer or local building inspector to confirm that they are happy to certify the installation before placing an order.

Pressure Testing

Airtight buildings very often have to have a pressure test. In other European countries they tend to complete the pressure test, then install the stove and flue. Sometimes Building Control insist the wood stove and flue are in place before the pressure test is carried out. This should involve blocking off all 'holes' in the skin of the building, including the direct air supply duct to the woodburning stove and the flue. Sometimes the flue is not blocked off for the test, this means you will get very small leakage of air through the appliance (even 100% air-sealed stoves will leak a tiny amount of air) and through each join in a twin-wall flue system. This is not regarded as a problem by any of the designers and architects we have spoken to.

A Discussion of Building Regs

Some Building Control Officers and Approved installers will insist on a 'non-closeable' room vent in the wall as well as the direct air supply to the solid fuel stove. There is an argument for this being detrimental to the design and operation of the new build house; as if you have spent a great deal of time money and effort to make your house air tight, why would you want to put a big hole in the wall?

The argument boils down to this:

Building Regs suggest an OPEN FLUED APPLIANCE must have a 'permanently open air supply' to it. Refer to section 1.2, and diagram 8, pages 17/ 18 of Approved Document J.

Some woodburning stove installers feel that because the stove door has to be opened to the room to refuel, it has to be classed as an 'open flued appliance'.

Approved Document J makes no reference to refuelling in this instance.

The definition of an OPEN FLUED APPLIANCE is 'one which draws it's combustion air from the room or space within which it is installed...'. See Section 0 - 04.33. Page 15 Approved Doc J.

The definition of a ROOM-SEALED appliance is 'an appliance whose combustion system is sealed from the room in which the appliance is located and which obtains air for combustion from a ventilated uninhabited space within the building or directly from the open air outside the building....'. See Section 0 - 04.38. Page 16 Approved Doc J.

So, after all that, what is the conclusion?

It is always down to the stove installer to interpret Approved Document J into a safe, sensible, and efficient installation. This information is simply here to inform you of some of the potential pitfalls.

There is an Amendment to Approved Document J on it's way soon which will clarify these points for everyone.


stovesonline saving on C02 stovesonline work with the international tree foundation. We look after 2 trees for every stove we sell stovesonline are members of regensw
you can pay for your stove with us by Paypal pay for your stove by visa pay for your stove by mastercard pay for your stove by maestro pay for your stove by delta card


Stovesonline Ltd, Flightway, Dunkeswell Business Park , Dunkeswell , Devon , EX14 4RD
0845 226 5754, info@stovesonline.co.uk, Contact Us
© Stovesonline Ltd. VAT: 801261871, Company: 04636920. Registered in England, UK