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Space heating

see also

It is reckoned that in the UK, housing is responsible for about 25% of greenhouse gas emissions. Poor heating can render parts of dwellings virtually unusable, partly through discomfort due to cold and drafts and partly through the damage caused to contents through condensation, dampness, mould growth, etc. effectively reducing the house size because you can’t use parts of it. Couple this with rising energy costs and the danger of CO2 pollution and there is every reason to put a lot of thought into the design of the heating system.

Although zero carbon houses are possible (and set to be mandatory by the EU for new build by 2021 – see the EPBD), probably the best practical examples of low energy building are Passivhaus. The beauty with Passivhaus is that the heating load is so small that no conventional heating system such as central heating is required. Almost all the heat is derived from the activities of the occupants and from sunlight, with only a very small fraction of heat needing to be introduced into the incoming ventilation air.

Unless you have a large source of free non-polluting heat such as geothermal then the best type of heating is the least. This means large amounts of insulation and airtightness and also good heating controls.

The main issues around heating which need to be considered are –

Other points may be important such as whether a heating circuit can be split or metered differently should the house be divided up differently in the future, say into two smaller flats. See Flexible design

The maintenance aspect of heating can be considerable with costs currently running around £200 p.a. for a gas boiler if you have insurance and do scheduled maintenance.

The subject of cooling in summer may have some bearing on the heating system

Combined heat and power

This is mainly dealt with here because it is still an emerging technology. If you should decide to try it then you need to do several things

  • estimate carefully the likely energy use of your house for both electricity and heating
  • check you can do net metering. see Energy harvesting
  • get as much up-to-date information as you can from suppliers and ask to talk to some of their existing customers
  • remember you might need to allow extra space for the boiler
  • you may need space for a water accumulator
  • try to contact other people who have a wider experience of CHP use

It is becoming possible to generate electricity from a wood stove at the same time as getting heat. The Austrian SPM company have integrated a Stirling engine into a wood pellet stove. It produces up to a kilowatt of electricity. It is not clear whether development is still ongoing with this product

Stiirling engine generator

Stirling engine generator

See also the Sunmachine wood pellet generator

Hearths

see also Chimneys

The Building Regulations (Approved Document part J) stipulate what type of hearth is required for various stoves and heaters and other issues such as combustibility of the surrounding areas. Chimneys are also covered by the regs and it should be noted that if a stainless steel twin wall flue is used then (depending on the manufacturer) the specification will vary between different types of fuel such as gas, coal and wood.

The main sections of the Approved Documents, part J, dealing with hearths are

  • the definition of the word ‘hearth’, along with its function
  • walls adjacent to hearths
  • construction of hearths
  • bases for back boilers

Flues serving wood stoves have a tendency for tar to build up on the inside and then catch fire. This is more likely if the inside surface becomes cool due to the length of the flue or lack of insulation round the flue or burning damp wood. This is why a special type of flue is required for wood burning. It needs to be able to withstand quite a fierce fire which would never happen in a flue serving a gas fire.

Many stove suppliers and installers will give advice on this.

Very often you are forced to use a concrete hearth built into a floor and if the underside of this area is facing down into an unheated area such as a cellar then it is very important to insulate it heavily. Uninsulated, it will be a major heat loss downwards but if it is well insulated it can act as a heat store for any radiant or conducted heat coming off the appliance.

insulated hearth construction

 insulated hearth construction

Air supply to stoves

All combustion appliances require an air supply and wood burning stoves are no exception. As houses become more airtight, the correct design of air supply becomes more of an issue. Many stoves are now designed so that a combustion air supply pipe goes directly to the stove rather than the stove getting its air from the room. This also cuts down on cold drafts within the room. Recent developments with balanced flue wood pellet stoves mean you can locate the boiler on an external wall without a conventional flue or chimney just like a balanced flue gas boiler. See the Swedish Ariterm Arrow system.

Building Regulations

There are several Regulations which have a bearing on space heating:

Fire safety

With most forms of construction there will be implications concerning fire safety. These are covered in the Building Regulations and you can see examples of how to conform with these in Part B (Fire Safety)

Combustion appliances and fuel storage has a detailed section in the Approved Documents (part J) and this makes reference to several aspects of the design and construction of houses including:

  • the construction of chimneys and flueblock chimneys along with wall thicknesses
  • hearths, gathers, and bases for back boilers for gas fires
  • fireplaces including large and unusual ones
  • flues and their sizing including flues for gas appliances
  • flue heights and how flue outlets relate to roof design and adjacent buildings
  • ventilation and air supply for appliances (this has a large bearing on ventilation and air tightness generally).
  • fire resistance of construction close to an appliance
  • the testing and repair of old chimneys
  • storage of gas bottles and oil tanks

Combustion appliances and fuel storage has a detailed section in the Approved Documents (part J) and this makes reference to several aspects of the design and construction of houses including:

  • the construction of chimneys and flueblock chimneys along with wall thicknesses
  • hearths, gathers, and bases for back boilers for gas fires
  • fireplaces including large and unusual ones
  • flues and their sizing including flues for gas appliances
  • flue heights and how flue outlets relate to roof design and adjacent buildings
  • ventilation and air supply for appliances (this has a large bearing on ventilation and air tightness generally).
  • fire resistance of construction close to an appliance
  • the testing and repair of old chimneys
  • storage of gas bottles and oil tanks

Conservation of Fuel and Power  (Part L of the Regulations) concerns energy saving and it distinguishes between new dwellings (part L1A)  and existing ones (part L1B).

L1A has two key sections dealing with energy saving:

Section 4: Design standards

  • Target CO2 Emission Rate (TER)
  • Buildings containing multiple dwellings
  • Calculating the CO2 emissions from the actual dwelling
  • CO2 emission rate calculations
  • Secondary heating
  • Internal lighting
  • Buildings containing multiple dwellings
  • Achieving the target
  • Fabric standards
  • System efficiencies

Section 5: Quality of construction and commissioning

  • Party walls and other thermal bypasses
  • Thermal bridges
  • Air permeability and pressure testing
  • Alternative to pressure testing on small developments

 

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