How to choose a convector for a panoramic window
By a panoramic window, cold air slides down the glass and “flows” along the floor. The convector must intercept this stream at the glass line, so it is placed along the window rather than somewhere nearby: a short section to the side will leave a cold track in the middle.
What length is needed
A reference: a length close to the glazing width. This is a starting point, not a calculation. How much heat the room needs is calculated by an engineer from the heat losses, while the calculator on the site gives only an approximate selection.
A short section also gives less per metre. S/C 90, natural convection, one heat exchanger, 85/75: 303 W at 1000 mm, 770 W at 2000 mm and 1238 W at 3000 mm. One 3000 mm casing gives 15% more than two of 1500 mm (1238 versus 2 × 537 = 1074 W). Where the window and the installation allow, a long unit is more efficient than a row of short ones. In the tables the lengths reach 3000 mm; wider glazing is covered by several units in a line.
If the floor is already finished, see what to use instead of an in-screed convector. A calculation with an example is in the material on choosing a convector for a panoramic window.
Natural or forced convection
If the room is heated by something else and the convector only cuts off the cold from the glass, natural convection is enough: it is silent. If it must heat the room itself, a version with a 24 V DC fan is needed. Here are S/C 90 and SV 90, 3000 mm long, one heat exchanger, W:
| Mode | Natural | Fan 30% | Fan 50% | Fan 100% |
|---|---|---|---|---|
| 85/75 | 1238 | 1846 | 3035 | 4554 |
| 65/55 | 825 | 1417 | 2203 | 3170 |
| 45/35 | 412 | 916 | 1394 | 1910 |
| Noise, dB | — | 19,8–24,3 | 25,4–29,0 | 40,5–46,0 |
The noise is given per the datasheet for lengths 1000–3000 mm; the S/C 90 fan consumption is 10–20 W. At 45/35 a fan at 30% more than doubles the output: 412 → 916 W. Our position: better a fan with a reserve at low speed than natural convection at the limit, and the 24 V line, the power supply and the thermostat are built in before the screed is poured.
Heat pump and condensing boiler
Carrera’s tables have three modes: 85/75 for a classic boiler, 65/55 for a modern boiler, 45/35 for a heat pump. Take 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). Even 3000 mm of the same unit gives only 337 W at 45/35. So on a heat pump the output is taken from the 45/35 row, not from the catalogue, and it is usually a version with a fan. Details in the review of a convector at 45/35.
Which series fits into the screed
The casing height must fit into the screed together with the layer under the unit, so the series is chosen by the actual depth under the glass. All the series are gathered on the in-floor convectors page, and here is what matters specifically for glazing:
| Series | Casing height, mm | Width, 1 heat exchanger, mm (natural / with a fan) | Fan consumption |
|---|---|---|---|
| M/C 65 | 65 | 230 / 250 | 15–30 W |
| S/C 90 | 90 | 230 / 250 | 10–20 W |
| 4S | 110 | 180 / 200 | 10–20 W |
| S/C 120 | 120 | 230 / 280 | 30–60 W |
For pools, winter gardens and SPAs there is Hydro, 105 and 120 mm high. The decision on the series is made before the concrete work.
What goes wrong and when a convector is not suitable
- A short unit in the middle. The watts add up on paper, but a cold track remains at the edges of the glass.
- A catalogue figure on a heat pump. S/C 90 at 2000 mm: 770 W at 85/75 and 256 W at 45/35. The shortfall shows on the glass in the very first winter.
- A floor-length curtain or a sofa over the grille. Warm air doesn’t rise along the glass, and the curtain disappears.
- Condensation at the bottom of the glass in frost. Often it’s a weak or blocked flow, not a window defect; how to tell is described in the material on condensation on panoramic glass.
- The screed is poured or thinner than 65 mm. An in-floor unit is out; what remains is a floor-standing FRH or a skirting BR.
How to check that the curtain works
- In frost, when the system has reached its mode, compare the lower edge of the glass in the middle and near the edges with your hand or a non-contact thermometer. A cold spot means the curtain doesn’t reach there.
- The glass doesn’t fog up at normal room humidity.
- The fan at night speed can’t be heard. If it can, and it only heats at high speed, the output is insufficient.
- The output is taken from the row for your mode, and the supply and return are given in writing by the designer.
Is one convector enough for the whole window?
By length — up to 3000 mm in Carrera’s tables; wider, several units are placed in a line. By output it depends on the heat losses and the coolant mode, so the configuration is calculated by an engineer.
The window is already in, the screed isn’t yet — is that OK?
That’s the best moment. Send the glazing dimensions, the ceiling height, the coolant mode and the future screed depth: the casing will be set to the right depth, with no rework.
Can the convector be covered by a curtain or a sofa?
No. A cabinet or sofa over the grille blocks the heat flow, and a floor-length curtain keeps it behind itself. The curtain along the glass then doesn’t form.
Is a fan needed by a panoramic window?
Not always. It’s decided by the unit’s role and the supply: at 45/35 even 3000 mm of S/C 90 without a fan gives only 412 W. At 85/75 the same 3000 mm gives 1238 W, and for a curtain from the glass that may be enough.