Sizing convection panel heaters: the method
A convection panel heats the air that passes over its element. Warm air rises out of the top grille, spreads across the ceiling and sinks as it cools, creating a slow loop of air around the room. To keep the room at your target temperature, the panels must replace the heat that escapes through walls, windows, floor, ceiling and drafts.
The planner estimates each room’s heat loss with the standard volume method:
Heat need (W) = L × W × H (m³) × (T_indoor − T_outdoor) (°C) × insulation factor × wall factor × window factor
The insulation factor is about 0.6 W/m³·K for a high-performance new home, around 1.2 for a typical older house and 1.7 or more for a drafty building. Rooms with more exterior walls and more windows lose more heat, so they get a higher multiplier. The result is rounded up to standard panel sizes, with roughly a 10% reserve so the room can recover after a door is opened.
Where to put the panels
- Under windows. The rising warm air blocks the cold downdraft from the glass. In rooms with two windows, two smaller panels usually feel more even than one large panel.
- On exterior walls, about 4–6 in (10–15 cm) above the floor, so air can enter at the bottom.
- Keep curtains, shelves and furniture away from the top grille, and never cover a panel with clothes.
- In bathrooms, use only panels rated for wet zones (for example IP24) and follow local zone rules.
Thermostats make the difference
Panels with a mechanical thermostat let the temperature swing by 1–2 °C, which wastes energy and feels less comfortable. An electronic thermostat holds the room within about ±0.2 °C, and a programmable or Wi-Fi model lets you lower the temperature at night and while you are out. The planner applies a typical saving of about 7% for electronic and 12% for programmable controls.
Common panel sizes
| Rated power | Typical width | Room it suits (average insulation) | Current at 120 V / 240 V |
|---|---|---|---|
| 500 W | ≈ 18 in / 45 cm | Small bathroom, hallway, 40–60 ft² (4–6 m²) | 4.2 A / 2.1 A |
| 750 W | ≈ 22 in / 55 cm | Small bedroom or office, 60–90 ft² | 6.3 A / 3.1 A |
| 1,000 W | ≈ 26 in / 65 cm | Bedroom, 90–120 ft² (8–11 m²) | 8.3 A / 4.2 A |
| 1,500 W | ≈ 33 in / 85 cm | Large bedroom or kitchen, 130–180 ft² | 12.5 A / 6.3 A |
| 2,000 W | ≈ 41 in / 105 cm | Living room, 180–240 ft² (17–22 m²) | 16.7 A / 8.3 A |
| 2,500 W | ≈ 49 in / 125 cm | Large living area, 240–300 ft² | – / 10.4 A |
Widths vary by brand and by low-profile versus standard-height models; check the spec sheet of the model you choose.
Wiring and circuits
Hard-wired panel heaters are continuous loads, so electrical codes generally limit them to about 80% of the circuit rating. A 120 V, 15 A circuit can carry about 1,440 W of heaters, a 240 V, 20 A circuit about 3,840 W, and a 230 V, 16 A circuit roughly 2,900 W. The planner groups your panels into circuits on that basis. Ask a licensed electrician to confirm wire sizes and breaker capacity before installation, especially when you add several kilowatts of heat to an existing panel.
Are convection panels expensive to run?
Like every electric resistance heater, a panel converts 100% of its electricity into heat. A 1 kW panel running for one hour uses 1 kWh, whatever the brand. What changes the bill is how many hours the elements are actually on, which depends on the room’s heat loss, the thermostat and your schedule. Panels are a good fit for well-insulated homes, apartments, extensions and rooms that are used part of the day. For a large, poorly insulated house used all day, a heat pump usually costs far less to run.