Stove and Liner Regulations
Is the construction hearth suitable?
The construction hearth is the area below the decorative hearth. Hearths should be constructed of suitably robust materials and to appropriate dimensions such that, in normal use, they prevent combustion appliances setting fire to the building fabric and furnishings, and they limit the risk of people being accidentally burnt. The construction hearth should be 125mm thick.
If the appliance is not sitting in a fireplace recess and it has been independently certified that it cannot cause the temperature of the hearth to exceed 100oc then a construction hearth may not be required but a non combustible decorative hearth of at least 12mm thick will still be required to Hetas guide part 3 and Document J building regulations sizes.
If it cannot be proven the heat below the appliance will not reach 100oc the minimum size would be 840mm square.
Is the decorative hearth suitable?
The decorative hearth should show a difference in height from the floor of at least 12mm to provide a warning to the building occupants and to discourage combustible floor finishes such as carpets from being laid to close to the appliance. Again there are specific distances from the appliance for the finish size of the hearths which can be found in Document J building regulations.
The basic requirements for a decorative hearth under a stove would be at least 150mm deeper from the rear of the stove and 150mm wider either side of the stove and 225mm from the front of the stove if it is a closed appliance or 300mm from the front of the stove if it is an open appliance or one that can be used with the doors open. These sizes can be found in Document J building regulations.
If the existing decorative hearth is flush to the floor then a suitable fender will be requires to provide the protection.
Is the chimney sound to use for gas or solid fuel?
Current regulation BS5871 part 3, BS5440 Part 1, BS6461 and Document J building regulations state that prior to any appliance being fitted, the chimney must be tested and swept to ascertain whether it is safe to use for either gas or solid fuel. We have a list of registered chimney sweeps that we use to carry out these tests. The result will either be a pass or failure due to the chimney leaking or being blocked. Minor repairs can sometimes solve the problem but in most cases where the chimney fails the test re-lining is required. Information on re-lining chimneys can be found in Document J building regulations and Hetas guide part 3. If the chimney is sound then the sweep will give you a working opening size which is the size we would work to for calculating slips or a final opening size.
If the chimney fails the integrity test then the flue will have to be re-lined.
We use a flexible flue liner for this which complies with current regulation and Document J building regulations. The liner is installed from the top of the stack once the chimney pot has been removed. Access to the stack has to be safe and in most cases a scaffold would be required. You would be responsible for arranging the scaffold if required.
The liner is terminated at the appliance end either by a specially made gather or a plate installed above the chamber or directly onto a register plate if a stove is being installed. The liner is then either insulated using vermiculite insulation or sealed to form an airtight seal between the top and bottom of the lining. The chimney pot is then replaced and a suitable terminal fitted.
As lining a chimney reduces the amount of surface area the chimney may not perform as it used to. Therefore we will carryout a spillage test to ascertain the new working opening size of the fireplace. The opening can be reduced by either new slips, or a glass header slip. If you require a larger opening size than the one calculated then you would have to have a fan system installed to pull the gases from the fireplace opening. (see fan systems)
Fans are used for either gas or solid fuel fires to increase the draw and allow a larger opening size than one calculated.
The fans are mounted on the top of the stack once the chimney pot has been removed. Unless there is already a route for the cable to power the fan we would use a heatproof Pyro cable down the flue to the fireplace chamber where it will be terminated in the final position of the fan controller. Access to the stack may require a scaffold to work safetly which you will supply.
For gas the fan has to comply with BS5871 regulations which state that there must be a fail safe device installed which will cut the supply of gas to the fire if the fan stops or there is a power cut. We install a gas solenoid valve in the gas line which provides this requirement.
For solid fuel there is not a requirement but we do have a system which will start a fan if heat is detected by the fire re-starting after it has been put out. This is an optional extra.
Fans are also used where there is no chimney and a flue system is installed. This is usually when a customer requires a new fireplace on or near an external wall in a room with no chimney. A fake breast is constructed and a flue system incorporated. The flue would normally run to ceiling height where it would turn 90 degrees and then exit through the external wall and terminate into the fan.
There are regulations which dictate where the fans can terminate which you can find in Document J building regulations and bfga.
All other regulations have to be followed for hearths and ventilations etc.
Gas and solid fuel appliances both need ventilation in the room of the appliance or if an internal room then through room ventilation would be required.
For a gas fire you are allowed 35cm2 of adventitious air which equates to 7kw of gas. Any gas fire under 7kw does not normally require additional ventilation in the room unless specified by the manufacturer. Over 7kw you would require 5cm per kw so an 11kw gas fire would require 20cm2 additional ventilation. This is worked out by 11kw – 7kw addventitous allowance = 4 kw x 5cm = 20cm2.
If you have two appliances in the same room then you would add the appliance kw together then deduct the adventitious allowance then x by 5cm2. Unless the manufacturer states otherwise.
All solid fuel and wood fired appliances require an adequate supply of air to ensure that the efficient combustion of the fuel occurs and the chimney functions correctly. Failure to provide sufficient air for combustion and ventilation into the room in which the appliance is installed can have very serious consequences. Smoking back will occur and the poor combustion of the fuel will increase levels of soot deposit and carbon monoxide which is a serious health hazard. Table 2.1 on page 24 of Document J building regulations gives values for the total free area of permanently open vents for several fireplace openings.
For solid fuel the calculation is slightly different to gas. You are allowed only 5 kw adventitious allowance and any appliance over 5kw would require 5.5cm2 per kw over.
If you are thinking of having a stove then it is not acceptable for one to be sited in a room that has an extractor fan fitted (unless it is re-circulating).