Anyone renovating the living room or thinking about a heat pump soon arrives at the question of how the heat will get into the room: through the floor, through large low-temperature radiators or simply through the radiators that are already there. The answer depends less on taste than many people think. What decides it is the temperature at which your future heat source can supply the heating water, the insulation of the home, the build-up and finish of the floor, and how much renovation you are willing to take on along the way. This article sets the options side by side and shows the best order in which to make the decisions.
Why the heat source determines the choice
A traditional boiler heats the water to 60 to 80 degrees and supplies it to radiators sized for that. A heat pump works differently: it extracts heat from the outside air or the ground and brings it up to temperature with a compressor. The smaller the difference between the outdoor temperature and the flow temperature, the less electricity that takes. According to Milieu Centraal (the Dutch independent information centre on energy and the environment), heat pumps supply heating water at a maximum of about 45 to 55 degrees, and a hybrid heat pump works at 30 to 55 degrees, with the boiler stepping in when it is very cold outside. This is called low-temperature heating (LT). As a rule of thumb, the industry speaks of LT at a flow temperature of no more than 55 degrees, compared with 80 to 90 degrees for high-temperature heating.
At a lower water temperature, a radiator gives off less heat. A radiator that heats a room at 75 degrees will no longer do so at 45 degrees, unless it is much larger or the house is much better insulated. Underfloor heating doesn't have this problem: the entire floor is the emitting surface, so a flow temperature of 30 to 40 degrees is enough. That is why underfloor heating and a heat pump so often come as a package. But it is not a law: large LT radiators or fan convectors do the same with less demolition work, and in a well-insulated house even the existing radiators may be big enough.
Insulate first, then choose
The better a home is insulated, the less heat it needs and the lower the flow temperature can be, whatever the heat emission system. Milieu Centraal only considers a home suitable for a fully electric heat pump if it is at least reasonably to well insulated: roof and floor with a decent layer of insulation, insulated cavity walls and HR++ glazing. For underfloor heating, there must also be very good floor insulation under the ground floor, otherwise you end up heating the crawl space too. So insulation comes before the emission system, and the emission system before the heat source. Which insulation measures deliver the most is explained in Improving your energy label: which measures really count?
A simple test shows where you stand. Milieu Centraal advises setting the boiler's flow temperature to 50 degrees for a whole winter (only the heating water, not the hot tap water). If the house stays comfortably warm even during a cold spell, the existing radiators are probably big enough for a heat pump. If it gets cold, you first need more insulation or a larger emitting surface. Many installers carry out the same check with a heat-loss calculation per room; ask about it.
Four heat emission systems compared
| Feature | Wet underfloor heating (screeded or milled) | Dry-build underfloor heating | LT radiators / convectors | Conventional radiators |
|---|---|---|---|---|
| Flow temperature | Approx. 30 – 40 degrees; max. approx. 45 | Approx. 30 – 45 degrees | Approx. 35 – 55 degrees | 60 – 80 degrees; sometimes lower with good insulation |
| Suitable for a heat pump | Yes, ideal | Yes | Yes, provided they are sized correctly | Only if generously sized and with good insulation; otherwise hybrid |
| Warm-up time | Slow (hours); night setback pointless | Moderate; faster than screeded | Fast | Fast |
| Demolition work and build-up height | Milling: floor stays at the same height; screeded: new screed, several centimetres higher | No breaking-out or pouring; a few centimetres of build-up | Limited: new radiators on existing pipes, sometimes thicker pipes | None |
| Floor finish | Tiles ideal; wood, laminate, vinyl (PVC) and carpet only with low thermal resistance | Same; watch the maximum load and flatness | Free choice | Free choice |
| Cooling in summer | Possible with a suitable heat pump | Possible | Fan convectors: yes | No |
| Tradesperson | Installer plus floor layer or tiler | Installer plus floor layer | Heating engineer / installer | Heating engineer |
The temperatures in the table are indicative; the actual value follows from the installer's calculation. For underfloor heating, Milieu Centraal gives a water temperature of no more than 45 degrees, with 30 degrees often achievable, and a maximum floor surface temperature of 29 degrees in living areas and 33 degrees in the bathroom.
Underfloor heating: wet, milled or dry
With a screeded floor, the pipes are laid on studded panels or a tacker board and embedded in a new sand-cement or anhydrite screed. This is the standard method in new builds and in renovations where the floor is being opened up anyway. The drawbacks are the build-up height, from a few centimetres upwards, and the drying time of the screed before tiling or laying can start. Milling is the renovation variant: channels are milled into the existing concrete screed, and the pipes are laid in them and finished off. The floor stays at the same height and doors and skirting boards don't need adjusting, but the subfloor must be thick and sound enough, and milling creates a lot of dust and noise. Dry build uses insulation panels with pre-formed channels that the pipes click into, covered with gypsum fibreboards or a thin levelling layer. No wet material is involved, the build-up is limited and the floor responds faster, which makes it attractive on upper floors and timber floors.
The floor finish also determines whether the system works. Tiles and natural stone conduct heat excellently; Milieu Centraal calls them the ideal finish. Wood, laminate, vinyl (PVC) and carpet are possible, but only if the thermal resistance of the finish stays low (Milieu Centraal uses a maximum Rd of 0.15 m²K/W) and the manufacturer approves the material for underfloor heating. Thick solid wood moves and shrinks with the temperature changes, and thick carpet blocks the heat. So discuss the finish with the installer before the pipes go in, not afterwards. A tiler who knows there is underfloor heating underneath will choose a flexible adhesive and grout and observe the prescribed heating-up schedule before the floor is put into use.
Milieu Centraal advises against electric underfloor heating and infrared underfloor heating as the main heating: they are not economical. As comfort heating in a small bathroom it is a different consideration, but don't count on it as a replacement for central heating.
Radiators as an alternative: LT radiators and the hybrid intermediate step
Not everyone wants to, or can, open up the floor. In that case low-temperature radiators are the alternative: radiators with a much larger emitting surface, or fan convectors that use a small fan to release the heat into the air faster. They often fit onto the existing pipes and in the same place as the old radiator, although they are deeper or wider. Many types can also cool in summer if the heat pump supports it. A correctly sized LT radiator does at 45 degrees what the old radiator did at 75 degrees, and without any demolition work.
People who haven't yet insulated well throughout often choose a hybrid heat pump alongside the existing boiler first. According to Milieu Centraal this is almost always possible, even with the existing radiators, because the boiler steps in on the coldest days and for hot tap water. The hybrid option is therefore a logical intermediate step: you save gas straight away, and as soon as the insulation and the emission system are in order, the boiler can still be removed. What exactly a heating engineer, installer or plumber does in this process is explained in Plumber, installer or heating engineer: who do you call for what?
Hydronic balancing: mandatory and often forgotten
Whichever emission system you choose, it only performs if every radiator or underfloor heating circuit gets exactly the amount of water it needs. This is called hydronic balancing (waterzijdig inregelen). Without balancing, the radiators close to the boiler get too much water and those at the end of the pipe too little, so the boiler or heat pump has to run unnecessarily hot and the house heats up unevenly. Moreover, since the Dutch implementation of the European EPBD III directive in 2020, balancing has been a legal system requirement under the Besluit bouwwerken leefomgeving (Bbl, the Dutch Building Decree): according to RVO (the Netherlands Enterprise Agency), radiators in homes must be hydraulically balanced after the boiler is replaced, there must be thermostatic radiator valves with flow control and there must be a suitable room thermostat. An exception applies only if the installation does not allow flow control, or if the additional control equipment costs more than 20% of the boiler replacement. When you get a new boiler or heat pump, explicitly ask your heating engineer for the balancing report.
Which tradesperson, and in which order
The process starts with an installer or heating engineer who calculates the heat loss per room, chooses the heat source and sizes the emission system. With underfloor heating, an underfloor heating company or installer is added to lay the pipes and connect the manifold, plus a floor layer or tiler to take care of the screed and the finish. With LT radiators, the heating engineer is all you need. If you are planning a larger renovation, the order is: insulation, then pipework and underfloor heating, then the screed and its drying time, then the finish, and only after that the balancing of the heat source. How these steps fit into the schedule is explained in How long does a renovation take: lead times per job. If you reverse the order and first buy a heat pump for a house that still runs at 75 degrees, you pay twice.