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Hydronic underfloor or radiators, which is best?

16 Nov
Hydronic underfloor or radiators, which is best?
News, Hydronics

Best form of heating:

The best form of heating is underfloor because it is delivered at over 30 degrees lower heat at just 26 degrees underfoot, which provides a comfortable, luxuriant warmth underfoot and is sufficient to make your whole house warm due to the larger surface area. Just like a cat lying on the bonnet of a car that’s just arrived home in winter, it doesn’t matter much if the space above your head is cold to feel warm because you are close to the heat source. This method of heating is particularly good for homes with high ceilings and large air volumes. 

If you are renovating your home then it may not be possible to install underfloor heating coils therefore wall radiators maybe the only option. Radiators are also easier to install if you have a suspended floor because you can usually run the water pipes to the radiators under the floor easily. 

Underfloor + Radiator Hydronic Heating:

Sometimes a combination of underfloor and radiators makes sense such as a renovation of a period home where there is an original suspended floor and a new extension built on a concrete slab. In this case, you will need to deliver the hydronic water at two different temperatures, around 60 degrees to the Radiators and around 40 degrees to the underfloor circuits which will conduct heat to the floor surface at 26 degrees. You can increase the water temperature to radiators above 60 degrees but this puts more pressure on your heating pipes and valves, wears the system more quickly and may scold toddlers who touch the radiators. It is better to have larger radiators and more temperate water.

Underfloor heating distributes heating and cooling evenly across the whole floor by radiating or absorbing heat whereas radiators rely on air convection to transfer heating and cooling to the middle of the floor and this can create differences in the feel of the heating and cooling across the whole floor.

Few Considerations:

  • Furnishings and windows: You need to find a space to put the radiators. If you have sash windows with space underneath, this can provide an ideal location for wall radiators. However, if you have windows that go down to floor level, this may compromise your options for furnishing your room and if you position couches or chairs against the radiators, this may create problems with your furniture, especially if the hydronic water temperature is above 60 degrees.
  • Hydronic Cooling: Underfloor will have a better cooling effect because of the larger surface area. Hydronic cooling can be provided by a heat pump operating in reverse mode, similar to an air conditioner except it is cooling the hydronic water which is making the floor cool and enabling it to absorb heat from the air above. Hydronic cooling works well because water is 3300 times more effective than air at absorbing and carrying heat. 
  • Air Movement: If you move air gently across the floor with a fan or some form of air movement, this will enhance the cooling effect. Ceiling fans are ideal because they move the air gently across the cool floor and make you feel about 4 degrees cooler at the same time. Similarly, radiators can take cold water and absorb heat but they have a smaller surface area which makes them less effective at doing this.
  • Fan Coils: A radiator coupled with a fan to draw the warm air through will be more effective at cooling because it speeds up the heat transfer process by convection. These radiators are called fan coils and may be an option where there is limited space and underfloor heating/cooling is not possible. A fan coil can also be placed inside drop ceilings above bathrooms or wardrobes just like a concealed air conditioning indoor unit. A fan coil can also dehumidify because it can take colder water below the dew point and catch the condensation drips in a tray that is taken out to a drain point.

Efficiency:

If you are generating most of your power from solar PV panels, then efficiency of power use is an important consideration.

For a heat pump, it is more efficient if the temperature in both heating and cooling modes is more temperate. For instance, a good heat pump in heating mode using 1kW of power can deliver 4.5kW of underfloor heating in a cold southern climate in winter, whereas the same amount of power will deliver about 3.8kW of heating through radiators.

Finally, for both methods of hydronic heating and cooling, reducing your heating and cooling load is a key consideration. If you can reduce the heating or cooling requirement, then you can reduce the size of the heat pump, reduce the size of your radiators and/or make the water more temperate and improve efficiency.

 

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