DIY Heating Plumbing Tips 1 - Underfloor Heating Design And Installation Guide


What Size Pipe Should I Use?

  • You should use a 16mm multi layered composite pipe (MLC) for underfloor heating as it incorporates an aluminum/aluminum layer within that acts as an oxygen barrier

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What is The Spacing Distance For The Clips?

  • The underfloor heating pipe clips should be spaced 1 meter apart. The pipes can also be tied to meshing layered on top of the insulation

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Where Do I Install The Edge Insulation?

  • The edge insulation is installed around all the perimeters of each room (solid and screed floors) with underfloor heating to prevent side heat loss, and to keep the heat contained within it's zone. Generally this is installed by the builder, however, you can purchase 20mm edge insulation from any builder's merchant

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How Will I Know The Length Of The Loop?

  • Each pipe loop (coil) comes in 100 meter maximum coil length which is marked every meter so enabling you to check the length of each loop
  • The 100 meter maximum coil length is linked to the head pressure from the pump which is only capable of pressurizing water through 100 meters of pipe
  • 100 meters of MLC pipe covers approximately 25m2, but don't forget to take into account the length of the flow and return feeder pipes from the manifolds to each room

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What Type Of Insulation Should I Use?

  • You can use polystyrene or polyurethane. Polyurethane out performs polystyrene and because of it's greater density you can use clips or rail clips. If you have enough space and are able to, use 50mm, if not then 30mm is the minimum recommended thickness
  • If you use polystyrene insulation a thickness of 50mm is recommended and as it has less density - a wire mess is placed on top of the insulation to which the pipe is tied

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What Pipe Spacing Do I Use For The Design Layout?

  • For new well insulated homes a spacing of 300mm (pipe center to pipe center) is recommended. For existing and older homes that are not well insulated then 200mm spacing should be used
  • You should always try to use the 100 meter of pipe whatever the size room rather than cutting the pipe, e.g, 300mm spacing in a room sized 23m2 and 200mm spacing in a room sized 15m2 as this would be a cost effective way of using MLC pipe. In the larger room the water flow rate can be adjusted to compensate for the wider pipe spacing. The 200mm spacing in the smaller room translates into a faster heating

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What is The Best Type Of Floor Finish?

Tile floor finish is the best for heat transfer as it is a good conductor of heat. If you choose carpet then a Tog value of less than 1.5 is recommended (Tog is the thermal resistance of a textile, the higher the value the higher the resistance)

Timber floors should have a moisture content of less than 10% this is to prevent shrinking; otherwise it should be left to naturally dry

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How should I Lay Out The Pipe - What Order?

The pipe should be laid in accordance to heat output importance which is simply:

  • Cold spots first like external walls
  • Internal walls second

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What distance should The Pipe be from The External Wall?

  • The pipe should be 100mm from the external wall
  • Areas of full length glazing can benefit with a few rows of 100mm spacing to off-set the increased heat loss from those areas of floor to ceiling glazing

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What Should The Flow Temperature and Temperature Difference Be?

  • The Flow temperature can vary between 35 and 60°C depending on your building heat loss and flooring type. The flow temperature (for underfloor heating systems using thermostatic mixing valves) for screed floors should be about 43°C and 55°C for timber/timber suspended and floating floors
  • The temperature difference between the flow and return pipes can range from 5 to 10°C

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How Does The Manifold Work?

  • The Manifold distributes the heated water to each room. The flow rate is controlled by the flow gauge on the flow pipe which can be adjusted manually (normally full flow rate is used with 100 meter pipe and half the flow rate if 50 meter or pipe is used)
  • If you wanted individual room control, thermostatic actuators wired to the room timers can be fitted to the return manifold.

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How Do I Fill The Underfloor Heating System?

  • The system is filled by using mains water pressure and vented (purged) of air
  • This is done through the end caps on the manifolds.
    • All the circuit valves on the manifolds should be closed
    • The flow end cap should be connected by a hose to the water main
    • The hose connected to the return end cap should be placed in a bucket by an external drain (the use of the bucket will enable you to see when the system is free of air as air bubbles will easily be seen)
    • Then one by one the flow and return valves are opened, the circuit purged of air and closed
    • Purge flow and return manifolds and close off, closing the return manifold first, then the flow manifold, and finally the water main outlet

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How is The System Tested?

  • The system should be tested before the screed and floor is laid at an air pressure of 6 bar (600kpa) for 24 hours. You are looking for air leaks which you will detect by a fall in pressure.

Note: When using screed flooring the screed must be allowed to dry for a minimum of 4 to 6 weeks before the heating is operated. As the system is used for the first time, the mixing valve must be set to minimum setting to let the moisture in the screed to dry out. The temperature should be increased by two degrees every day until the mixing valve is set at 43°C or 45°C.

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How Long Will A Multilayer Composite Pipe Last?

  • Multilayer composite (MLC) pipes normally have a 10 year manufacturer guarantee, but in fact can last 50 years or more if correctly installed

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What Are The System Components?

  • Apart from the manifolds and the underfloor pipe there is:
    • A 2 port motorized valve
    • A Pump
    • A 3 or 4 port mixing valve
    • A Programmable room thermostat - and individual room timers if needed

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What Size Pump Should I Use?

  • For floor areas up to 250 square meter use a pump that can deliver a 60 kpa head pressure, and for floor areas larger than 250 square meter use a pump with 80 kpa head pressure

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