A. Yes, wall mounted or floor mounted, gas or oil fired, combination boilers or standard boilers can be used, but the biggest advantage in efficiency will be obtained when a condensing gas or oil fired type is used as these boilers can take advantage of the lower return water temperatures occurring on underfloor heating systems.



Q. I am designing an apartment complex where space is at a premium. What is the smallest boiler I can use for underfloor heating?

A. There is an electric boiler on the market, that measures one metre long by 90mm square, that will run an underfloor heating system. It only weighs 9kg and is available in sizes 6kw, 9kw, 11kw and 12kw.



Q. What are the main components of an underfloor heating system?

A. Boiler, pipework, manifolds and the control system.



Q. What pipe do you use for underfloor heating systems?

A. Multilayer pipe which is aluminium sandwiched between layers of PEX pipe. All pipes should incorporate an oxygen barrier to prevent oxygen ingress into the system.



Q. Do underfloor heating systems operate at a lower temperature than a radiator system?

A. Yes, radiator systems will operate at a boiler flow temperature of 82°C and a temperature drop of 11°C, but an underfloor heating system will run at temperatures in the range of 35°C to 60°C depending on floor conditions and the type of building.



Q. Why do I need to use manifolds?

A. All the buried pipework in underfloor heating systems should be in continuous loops without joints. The flow and return from each loop of pipe is brought back to manifolds where the flow of water can be monitored and controlled. Individual rooms or areas can have their own room thermostats for local temperature control wired to low voltage actuator heads on the flow control valves. The advantages of using manifolds are that areas which are not required to be heated can be shut off, local modifications and additional pipe loops can be added without the need to drain the entire system, and the system can be balanced quickly and efficiently.



Q. What is the maximum loop length?

A. The maximum loop length of 100m must be used in all installations. It is not advisable to make the loops longer than 100m. The reason for this is due to the head pressure from the pump, the pump used is only capable of pressurising water through 100m of pipe. 100m of pipe will cover an area of approximately 25m2. For commercial installations where larger diameter pipe is used, the maximum is 140 metres.



Q. What are the lengths of each loop?

A. The pipe is marked every metre. This makes it very easy to check the length of each loop. When laying the pipe it is important to mark how long each loop is, this is to allow the flow gauges to be easily adjusted to the right levels The maximum length of a loop for domestic installations is 100 metres. For commercial installations the lengths can be longer, up to 140 metres, but a larger diameter pipe is used and the very large systems have booster pump sets.



Q. What type of insulation is to be used?

A. Use 50mm high density insulation below the pipes and 65 - 75mm of screed on top of the insulation. All installation work must comply with current Building Regulations. The mixing valve needs to be set at minimum temperature when commissioning the system. Increase the temperature by 2 to 3 degrees everyday. This will avoid the screed cracking.



Q. What is the water flow temperature?

A. The water flow temperature will vary between 35-60°C, depending on the heat losses from the building. If the system operates with thermostatic mixing valves, use 43°C temperature for screeded floors and 55°C temperature for timber suspended and floating floors.



Q. What is the heat output?

A. Maximum heat output from screeded floors is approximately 100 W/m2, the maximum heat output from timber suspended floor and floating floor is 70 W/m2. With there being higher standards of insulation in new buildings, average heat requirements for many buildings are now below 60 W/m2. For small bathrooms it is standard practice to also install warm water towel rails to give extra heat output as these areas are usually not very large.



Q. How do you fill the underfloor heating system?

A. The system should be filled with water and fully vented of air. This can best be achieved using mains water pressure through the two end caps on the manifold. All valves should be closed and the flow end cap connected with a hose to mains water, with the return end cap connected to a hose laid to waste water point. One by one flow and return valves are opened and closed on loop purging them of air.



Q. What is the working life of our pipe?

A. Our pipe has one of the highest approvals in the world from the Water Research Council (WRAC); 10 bar pressure and 95°C temperature. Our pipe is guaranteed for 50 years. When correctly installed and run, our pipe should have a working life in excess of between seventy years and one hundred years, provided that no oxygen has seeped into the pipe and that the system has not been run at excessive temperatures.



Q. Can you combine an underfloor heating system with radiators?

A.Yes, but there must be filters installed to avoid sludge from the radiators blocking the underfloor pipes.



Q. What is the required spacing between pipes on an underfloor heating circuit?

A.We recommend pipe centres of 200mm. Within 500mm of an external wall, pipe spacing should be reduced to 100mm



Q. Why should pipes be spaced closer together adjacent to external walls?

A. This is necessary to offset heat losses through glazing, external doors, patio doors etc.



Q. Why do I need to put insulation below the underfloor heating circuit?

A. Insulation will reduce heat loss through the floor construction, resulting in lower fuel bill. Also, the insulation assists in deflecting heat upwards resulting in quicker warm up periods and assisting in producing a constant floor surface temperature. Insulation is also essential to produce a floating slab construction.



Q. What does ‘floating slab construction’ mean?

A. The screed containing the underfloor heating circuits is separated by insulation underneath and around the perimeter from any part of the building structure. This allows the screed to expand and contract during the operation of the underfloor heating system without cracking or breaking up. This method of floor construction is called a ‘floating slab’

Q. What is a control pack?

A. A control pack consists of a pump, thermostatic mixing valve, zone valve and isolating vales combined with pipe fabrication to enable the control pack to connect directly to the manifolds



Q. What does a control pack do?

A. Thermostatic mixing valve – the thermostatic mixing valve ensures that the water circulates through the underfloor heating circuit at a constant temperature of 43 degrees C. This results in a floor surface temperature that is even and does not exceed 29 degrees C, or 27 degrees C for wooden floors.

Zone valve – the zone valve allows the underfloor heating system to be isolated via a programmer or room thermostat. The zone valve can also be utilised to send a signal to the boiler to fire when open.

Pump – the pump circulates water through the underfloor heating system. It also creates a head pressure, which overcomes the resistance created by the circuit, vales and manifold.