In-floor convectors: how they work
What a convector is made of
Four assemblies. The casing lies in the screed: stainless steel (Inox), painted steel (Black) or anodised aluminium (Alum), depending on the series; in Hydro the casing is stainless steel with a drainage hole. The heat exchanger: a copper tube with fins, of cassette type, it can be pulled out of the casing for servicing. The grille is the only thing visible in the interior. In versions with the letter V a fan direct-current 24 V is added. Warranty: 10 years on convectors and 2 years on the electrical part.
| Series | Height, mm | Copper tube | Fan | Casing |
|---|---|---|---|---|
| M/C 65 | 65 | Ø 18 mm | tangential DC 24 V | Inox, Black |
| S/C 90 | 90 | Ø 22 mm | DC 24 V, Ø 43 mm | Inox, Black, Alum |
| 4S | 110 | four tubes Ø 12 mm | DC 24 V | Black |
| S/C 120 | 120 | Ø 22 mm | DC 24 V, Ø 60 mm | Inox, Black, Alum |
| Hydro | 105 and 120 | Ø 22 mm | DC 24 V | Inox, drainage |
In the names, V means a fan, and the number 2 an additional heat exchanger. So SV 90 is S/C 90 with a fan, and S2 is a version with two heat exchangers.
Where the heat comes from
The glass cools the air next to it, the air gets heavier and drops into the casing through the grille. There it passes the fins, is heated and rises along the glass: thus a thermal curtain is formed. This movement is powered by the temperature difference, so the output depends on the coolant.
M/C 65, 1500 mm long, natural convection, one heat exchanger: 445 W at 85/75, 293 W at 65/55 (34% less) and 146 W at 45/35 (67% less). The ratio is close to 3 : 2 : 1, like the difference between the average water temperature and the room air (60, 40 and 20 degrees at +20 °C). A classic boiler runs at 85/75, a modern one at 65/55, a heat pump usually at 45/35.
| M/C 65, 1500 mm, W | 85/75 | 65/55 | 45/35 |
|---|---|---|---|
| Natural convection | 445 | 293 | 146 |
| Fan 30% | 963 | 664 | 400 |
| Fan 100% | 2070 | 1443 | 874 |
What a fan adds
It drives air through the fins faster, so the same casing (M/C 65, 1500 mm) gives 2.2 to 6 times more, depending on the mode and speed. The price is sound and electricity. M/C 65 makes 19.4–22.8 dB at 30% and 45.0–51.0 dB at 100% (range by lengths 1000–3000 mm), consumes 15–30 W. The noise is damped by anti-vibration inserts in the heat-exchanger mount and the fan platform. The speed is controlled by a thermostat, and a power supply converts 230 V to 24 V; about this on the automation page. Which speed you actually need is covered in the material on the fan’s noise, output and electricity.
What can go wrong
- An air lock. The start of the unit is hot, the end is cold: the convector doesn’t heat along its whole length.
- A mode lower than the one selected. Selected for 85/75, but the pipe runs at 45/35: a threefold shortfall, see the table above.
- A covered grille. A carpet or furniture over the casing doesn’t let the warm air out.
- No 24 V, or the thermostat doesn’t switch the fan on. The V-version tables then don’t apply to you: they were calculated for speed.
- Dust. Cleaning is described in the list below.
An in-floor convector won’t suit in three cases. There is no screed or it’s thinner than 65 mm: then a floor-standing or skirting unit. There is no water heating: for glazing without it there is the electric SE series at 220 V. Water gets into the casing, as in a pool or during wet cleaning: then Hydro.
How to check that everything works
- Supply and return on the unit: a working convector takes heat from the water, so the return is noticeably cooler. Almost equal — a reason to call an engineer.
- Warm air comes out through the grille along its whole length, not only on the supply side.
- The fan spins evenly, without knocking, and changes speed per the thermostat.
- Once a season the grille is removed without tools and the casing is vacuumed.
- First season and “doesn’t heat”: the diagnostic order is in the material what to do if the convector doesn’t heat.
Does a convector work without a fan?
Yes. Natural convection needs no electricity and is silent, but gives less: at 45/35 only a third of 85/75. For glazing with large losses, a fan or a second heat exchanger is added.
Can the fan be heard at night?
At 30% speed it gives 19.4–24.3 dB depending on the series and length, at 100% 40.5–52.4 dB. The night speed is chosen so that the output is enough even at low speed.
Does such a convector heat the whole room?
It depends on the version. Per the manufacturer’s description, versions with a fan (SV, CV) are intended for the main heating of rooms with large glazing and large heat losses, while natural convection is more often an additional source. Whether it’s enough for you will be shown by a calculation.
Is a convector suitable for a heat pump?
Yes, but the output is taken from the 45/35 row, where without a fan a third of the boiler figure remains. So it’s usually a version with a fan; in more detail in the review of a convector on a heat pump.