Sizing a Wall-Mounted Panel Heater for a Large Room

A distributor in Norway asked me last month why his 1500W wall-mounted panels were coming back as "not hot enough" from customers heating 30-square-meter living rooms. That's a sizing problem, not a product defect. Here's how to get it right before you place a PO.

The only formula that matters

Watts per cubic meter. Not square meters, not "it feels right." For a typical insulated European home with 2.4m ceilings, you need roughly 30 to 40 watts per cubic meter to hold 20°C when it's -5°C outside. That's a real number from our test room in Foshan, not a brochure figure.

Run the math on that Norwegian case. A 30m² room at 2.4m is 72 cubic meters. At 35W/m³, you need about 2500W. He was shipping a 1500W panel and wondering why people complained. Two panels, or one 2500W unit, solves it.

If the space is a garage, workshop, or basement with no cavity insulation, double it. 60 to 70W/m³ is realistic. An electric heater for garage use is a different animal from one for a bedroom, even if the casing looks identical.

Convection vs oil-filled vs infrared

Buyers ask me this every week. Short answer:

• Convection panel (our wall-mounted line): fastest warm-up, 3 to 5 minutes to feel heat, dries air slightly, silent. Good for bedrooms, offices, bathrooms with IP24 rating.
• Oil-filled radiator: slow, 15 to 20 minutes to full output, keeps radiating after the thermostat cuts. Good for rooms with people sitting still for hours. Heavy. Freight cost matters.
• Infrared: heats objects and skin, not air. Good for a workshop where the door opens constantly, or a greenhouse. Useless for a whole-room average temperature claim.

For a silent electric heater in a bedroom, convection wins. For an electric heater for workshop use where you're standing at a bench in a cold building, infrared is often the honest answer.

Wattage tiers we actually build

Standard SKUs from our line:

• 500W / 750W — bathroom, small office, RV campervan
• 1000W / 1500W — bedroom up to 15m², home office
• 2000W / 2500W — living room, large bedroom, small workshop
• 3000W+ — industrial fan heaters, three-phase options

A 12V electric heater for a campervan is a different product category entirely. Don't let a buyer talk you into treating a 12V 200W unit as a room heater. It's a cab warmer. Be honest with them and you'll keep the account.

Thermostats, WiFi, and what buyers actually pay for

Mechanical thermostat: cheap, reliable, ±2°C swing. Fine for a garage.

Digital thermostat with 0.5°C accuracy: this is what "best electric heater with thermostat" searches are really about. Buyers want to see a number on a display. It sells.

WiFi smart electric heater: adds maybe $8 to $12 to our BOM depending on module. Sells at retail for $40 to $60 more. If your market is Amazon US or DE, it's worth stocking. If your market is a trade wholesaler selling to installers, skip it. Installers hate pairing apps.

Certifications and the paperwork buyers forget

CE and RoHS are table stakes. UKCA if you ship to Britain. ERP Lot 20 compliance is not optional in the EU — your heater must have a thermostat, a timer, and either open-window detection or adaptive start. We build all four into the digital models as standard. If a factory quotes you a cheaper unit without ERP, they're either lying or selling you old stock.

IP24 for bathroom units. IP44 if it's going anywhere near a shower zone. Don't confuse the two.

MOQ, lead time, and the honest numbers

Our standard MOQ is 200 pcs per model, mixed container okay. Lead time runs 15 days for a repeat order on a stock SKU, up to 45 days for a private label electric heater with custom housing, logo, packaging, and a new controller board. Tooling for a new injection mold adds 25 to 35 days on top and around $3,000 to $6,000 depending on size and finish.

If a buyer wants 50 units to "test the market," we point them at a trading company. It's not worth setting up a line for 50.

Running cost — the question your buyer will ask

A 2000W heater running 8 hours a day at 50% duty cycle uses 8 kWh. At €0.30/kWh that's €2.40/day, or about €72/month. Compare that to gas and the answer depends entirely on local tariffs. In the UK right now, electric is roughly 3 to 4 times the cost per kWh of gas. In France or Norway with cheap nuclear or hydro, it's much closer. Tell your buyers to run the numbers on their own tariff, not yours.

One honest takeaway

Most "my heater is weak" complaints are sizing errors, not manufacturing defects. Before you blame the factory, measure the room in cubic meters and check the insulation. If you're sourcing from an OEM electric heater manufacturer in China and the sales rep doesn't ask you about room size, ceiling height, and insulation before quoting wattage, find another factory. We ask because we've seen the returns.