What is very low temperature heating?
Very low temperature heating (in Dutch ZLTV) is a heating system that runs on flow water below about 35 °C. It goes a step further than low temperature heating, where the flow water is at most about 55 °C. A traditional boiler-and-radiator system often runs at 70 to 90 °C.
How does it work?
The cooler the water, the less heat each square metre of emitter gives off. To get enough heat into the room anyway, a very low temperature system needs a very large emitting surface:
- Underfloor heating across (almost) the whole floor.
- Wall heating or ceiling heating.
- Possibly fan coil units, which use a fan to extract extra heat from the cool water.
Ordinary radiators are usually too small to heat a room at these temperatures.
Why use it?
- Efficient heat pumps: a heat pump works more efficiently the lower the temperature it has to produce. Very low temperature heating is therefore a good match for a (ground source) heat pump.
- Comfort: large, lukewarm surfaces give even radiant heat without hot spots.
- Heat networks: in some new developments homes are connected to a low temperature network, with a heat pump in each home raising the temperature further.
What the building needs
The system only works well in a home with low heat demand:
- Good insulation of floor, walls, roof and glazing.
- Airtightness: draughts and gaps cause heat losses the system cannot keep up with.
- Controlled ventilation, preferably with heat recovery.
In a poorly insulated existing home it is often impossible to heat comfortably with water below 35 °C. So have a heat loss calculation done before choosing this system.
Practical points
- Slow response: underfloor heating reacts slowly. Large night-time setbacks make little sense.
- Floor finishes: thick rugs or insulating floor finishes reduce heat output.
- Cooling: many heat pump systems can also provide gentle cooling in summer through the same pipes.
Related terms
- Low temperature heating
- Underfloor heating
- Wall heating
- Heat pump
- Heat recovery ventilation
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