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Warm Water Underfloor Heating
Frequently asked questions
and answers
1. How do I connect my underfloor heating system to the boiler?
The underfloor heating system should be connected to the boiler through the manifold. The manifold controls the heat requirement for the underfloor system by blending hot water from the boiler with cooler returned water from the floor circuits. Most boilers have a high output temperature (80-85°C) to cater for the other heat requirements of the dwelling (e.g. hot water cylinder, radiators and towel rails), which means that they should not be connected directly to the underfloor system.
2. Why do I need another pump on the manifold?
The pump circulates the water within the underfloor heating system and will continue to operate after the injector valve has closed and hot water is no longer being mixed with the return water. It is also required where the pump on the boiler would not achieve the required flow rates in the system.
3. Where should the manifold be positioned?
The manifold can be positioned virtually anywhere in the building, as long as there is enough heat output to supply the demand. However it is preferable to site the manifold centrally in the building to ensure pipe runs to circuits are kept to a minimum.
4. Will putting carpet over the underfloor heating have an effect on it?
Yes, carpet will slow the heat transmission down because of its thermal resistance. However this should not significantly affect the overall performance of the system. It is important that carpeting is specified as a requirement during the design of the system and that the correct underlay is fitted; this preferably should have a tog rating of less than I.
5. Will underfloor heating work with laminate flooring?
Yes, however care should be taken when selecting laminate underlay. The manufacturer’s advice should be sought regarding suitability for use with underfloor heating, as some laminate underlays are highly insulating.
6. Can underfloor heating be installed on a pressurised sealed system?
Yes, it can be installed on any sealed or open vented type system.
7. How long does underfloor heating take to work?
Normally from cold, a typical solid floor system will take 3-5 hours to reach temperature. However when the system is operational, it will only lose on average 4°C in an 8 hour period, therefore it will only take a couple of hours to reach operating temperature in normal operation.
8. What type and thickness of floor insulation should be used?
Any board type of insulation can be used. However the foiled high-density polyurethane foam is likely to suffer less site damage due to the high compressive strength. Pipe fixing staples also hold very firmly into this type of insulation. The thickness of insulation required is calculated to achieve a U-value of 0.25, which is the minimum permitted by the Building Regulations. Insulation thickness will therefore be different for every building and should be calculated when designing the building.
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9. What type of screed do I use?
In most cases normal sharp sand and cement mix can be used for a standard 75mm screed. If the screed is to be less than 75mm other options should be considered. Advice should be sought from a screed manufacturer as additives and fibres can be added for additional strength and flexibility. For very thin screeds a special mix is required, however there is a possibility that the floor temperature will not be even, with warm strips above the pipe centres.
10. Do I need to add a plasticizer to the screed mix?
No, however it is important when screeding an underfloor heating system that the screed envelopes the pipe fully for it to work to its full potential. Screed is normally installed very dry, therefore care must be taken to avoid air pockets around the UFH pipe. Adding a plasticizer to the mix can help the screed flow better, thereby avoiding air pockets. Screed as a wet mix should be avoided because this can cause shrinkage and cracking when drying out. It is advisable to seek expert advice from a screed manufacturer.
11. What is the edge insulation strip for?
Edge insulation strip serves two purposes. Firstly it forms an insulation barrier around the floor slab and therefore prevents heat loss to surrounding walls. Secondly, it acts to fill the expansion gap around the slab, allowing the floor to expand and contract as it warms up and cools down.
12. What is the conduit used for?
On screeded installations the conduit is installed over the underfloor heating pipes, where they cross into adjoining rooms (generally at doorways). This is important because if a room is heated and an adjacent room is not, the floors expand in different directions and the pipe passing through the doorway could be damaged. The conduit pipe can also be used to sleeve underfloor heating pipe when it passes through an area that is not to be heated, e.g. under kitchen units.
13. What pipe spacing should I use?
Giacomini underfloor heating systems are individually designed. Please refer to your design data sheet or call our design office.
14. How is the system controlled?
Electrical actuator heads are fitted to each underfloor heating pipe circuit. These actuators are controlled either by a central thermostat or individual room thermostats, linked together with a time clock through a wiring centre. A weather compensation circuit may also be incorporated in the system to adjust for outside temperature variations.
15. How much water will there be in an underfloor heating system?
An 18mm pipe will contain .154 litres per lin metre of pipe. In addition there will be an amount of water in the manifold and pump.
16. Can I put a manifold in the floor and feed up?
Yes, however air locks may occur.
17. Can corrosion inhibitors be used in the system?
Yes, Giacomini recommend the use of corrosion inhibitors such as Sentinel 100 or Fernox MB in all systems.
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