Why 12V Electric Heaters Fail in Real RV Use

Most 12V heaters sold for RV and campervan use are a bad fit for the job. Not because they're poorly made, but because the math doesn't work. A typical 12V outlet in a van is fused at 15A. That's 180W max. Run it for an hour and you've pulled 15 amp-hours from your battery bank. A 200Ah lithium setup gives you maybe 10 hours before you're at 50% depth of discharge, and that's if you're not running anything else. Most people are.

So when a distributor asks me to quote a 12V heater for campervans, I ask what wattage they're targeting. If they say 300W or 400W, I tell them to check the fuse box first. A 400W draw at 12V is 33A. That's a 40A circuit. Most vans don't have one.

What Actually Works in a Van

The honest answer is that 12V electric heaters are niche. They work for small spaces with good insulation and a big battery bank, or for short bursts while driving when the alternator is charging. For overnight heating, you're better off with a diesel heater or a propane unit. That's not what buyers want to hear, but it's true.

Where 12V makes sense: keeping the chill off a small campervan while you're parked and plugged into shore power, or as a supplemental heater in a truck cab. I've seen 150W to 200W units work fine for that. Anything above 250W starts to demand real electrical infrastructure.

If you're sourcing for the RV market, look at 12V heaters with a low wattage electric heater design, 150W to 200W, and a built-in thermostat. The thermostat matters more than the wattage. Without it, you're just dumping heat until you manually shut it off. With it, the heater cycles and your battery lasts longer.

The 12V vs 120V Question

Here's where buyers get confused. A 1500W 120V heater pulls 12.5A from a standard household circuit. That same 1500W at 12V would pull 125A. You'd need 4/0 gauge wire and a dedicated 150A circuit. Nobody does that in a van.

So the real comparison isn't 12V vs 120V. It's 12V vs 120V through an inverter. If you're running a 2000W inverter, you can power a 1500W 120V heater. But the inverter itself draws about 10% overhead, so your 1500W heater actually pulls closer to 1650W from the battery. That's 137A at 12V. Still a lot.

For most campervan builds, a 500W to 800W 120V heater through an inverter is the sweet spot. It'll take the edge off a small space, and it won't destroy your battery bank in two hours.

What to Look For When Sourcing

If you're a distributor or private-label brand looking at 12V heaters, here's what I'd check:

• Fuse rating. The heater should have an inline fuse or a clearly marked amp draw. If the supplier can't tell you the amp draw at 12V, walk away.
• Thermostat type. Mechanical thermostats are cheaper and more reliable. Digital ones are nicer but add cost and a point of failure.
• Cord length and gauge. A 12V heater pulling 15A needs at least 14AWG wire. 16AWG will get hot. I've seen it.
• Certification. For Europe, you need CE and RoHS. For the UK, UKCA. For North America, ETL or UL. Don't accept "CE compliant" without a test report.

MOQ for a custom 12V heater is typically 200 pcs. Lead time runs 15 to 45 days depending on whether you're using an existing housing or tooling a new one. If you want a private label electric heater with your own logo and packaging, add a week for artwork approval and a week for production samples.

The Honest Takeaway

12V electric heaters are a hard sell for anyone who actually lives in their van through winter. They're fine for occasional use, for keeping the edge off, or for truck cabs. But if a customer tells you they want to heat a campervan overnight on battery power alone, steer them toward a diesel heater. You'll lose the heater sale, but you'll keep the customer. And they'll come back for the 120V units you sell for garage and workshop use, where the math actually works.

If you're sourcing 12V heaters, focus on the 150W to 200W range with a thermostat and a clear amp rating. That's the honest product. Everything above that is a battery killer with a nice label.