Quick Answer: For most barns, the Camplux BW264-N (2.64 GPM, 68,000 BTU) is the best tankless water heater — it fires on 2 D-cell batteries with zero electrical hookup, so a winter power outage can’t disable it the way one can disable a permanently plumbed unit’s freeze protection. For a heavier wash rack, the Eccotemp L10 steps up to 3.0 GPM on the same battery-only setup. If your barn already has real electrical service and you’d rather skip propane, the Rheem RTEX-13 is a 13 kW electric option rated up to 3.17 GPM. The mistake most barn owners make isn’t picking the wrong GPM — it’s assuming a whole-home unit’s “freeze protection down to -30°F” marketing claim still holds once the power is out, which per Rinnai’s own guidance it doesn’t.
Most tankless buying guides for an outbuilding start with GPM and BTU. For a barn, the first question should be power reliability, because a barn is one of the more likely places on a property to lose electricity in exactly the kind of winter storm that also threatens to freeze your plumbing. This guide covers the three realistic setups — battery-only propane, a step-up battery-only propane for heavier use, and electric for barns with existing service — and explains why the “built-in freeze protection” spec on a whole-home unit is less reassuring in a barn than it sounds.
The freeze-protection catch most barn buyers miss
Rinnai’s own freeze-protection guidance explains that its units’ built-in freeze protection relies on continuous electric power to run the internal heating elements and sensors that keep water from freezing inside the unit — and that’s precisely why Rinnai sells a separate mechanical Freeze Protection Drain-Down Kit as a backup, so the unit drains itself automatically if power is lost. That single fact flips the usual logic of buying a bigger, more feature-rich whole-home unit for a barn. A house with buried service, a generator, or a utility company that prioritizes residential restoration is a relatively safe bet for an electronically freeze-protected heater. A barn fed by an older overhead drop, with no backup power and often the last structure reconnected after a storm, is close to the worst-case scenario for that same protection.
The practical fix barn owners actually use isn’t a better freeze sensor — it’s sidestepping the dependency on power altogether. A battery-ignition propane unit like the Camplux BW264-N or Eccotemp L10 doesn’t need grid power to run at all, and when temperatures drop near freezing between uses, the standard move is simply to drain it and bring it inside, the same way you’d treat a garden hose. That’s a more reliable posture in an unheated outbuilding than trusting a sensor that stops working the moment the lights go out.
Our top picks at a glance
| Model | Best for | Fuel / Power | Flow / BTU | Power needed | Price |
|---|---|---|---|---|---|
| Camplux BW264-N | Best overall for most barns | Propane (LP) | 2.64 GPM / 68,000 BTU | 2 D-cell batteries | ~$240–300 |
| Eccotemp L10 | Best for a heavier wash rack | Propane (LP) | 3.0 GPM / 75,000 BTU | 2 D-cell batteries | ~$319–399 |
| Rheem RTEX-13 | Best electric (barn has a sub-panel) | Electric 13 kW · 54A | Up to 3.17 GPM | Dedicated 240V circuit | ~$255–365 |
1. Camplux BW264-N — Best Overall for Most Barns
Camplux 2.64 GPM Portable Propane Tankless Water Heater (BW264-N)
- Fires on 2 D-cell batteries with zero wiring or outlet needed — the pick for a barn or run-in shed that has a propane tank and a hose bib but no reliable, backed-up electrical service.
- CSA safety certification with a flame-failure device and overheat protection built in, the same model this site already recommends for cabins and off-grid outdoor showers.
- 2.64 GPM at 68,000 BTU clears the real-world flow most single-fixture wash racks need, well ahead of the roughly 1.4–1.5 GPM dedicated portable equine-washing systems target.
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The BW264-N is the right default for a barn because it needs nothing from the building except a propane tank and a water line — no circuit to run, no panel capacity to check, and no electronic freeze sensor that stops working the moment a storm takes the power out. It’s outdoor-rated only, so the plan is to drain and store it once temperatures drop near freezing between uses, not to leave it plumbed in and hope. See our full Camplux lineup for the RV-permanent and ultra-light options if your setup differs from a straightforward wash rack.
2. Eccotemp L10 — Best for a Heavier Wash Rack
Eccotemp L10 Portable Propane Tankless Water Heater
- Same battery-only, zero-electricity setup as the Camplux above, but with more BTU and GPM headroom for a barn washing several horses back to back or running a hose and a utility sink at once.
- 75,000 BTU at 3.0 GPM is enough for one shower, an outdoor wash-down station, or a bunkhouse sink, per Eccotemp's own spec sheet — but it isn't built or vented for whole-barn plumbing to multiple rooms.
- Like the BW264-N, it's a drain-and-store unit for winter, not a permanently plumbed, freeze-sensor-dependent install.
If one horse at a time isn’t your reality — a boarding barn with several wash stalls in rotation, or a wash rack that also feeds a utility sink — the L10’s extra GPM over the BW264-N buys some margin without giving up the no-electricity advantage. See our full Eccotemp lineup for the whole-home Builder Series if you’re also trying to supply a barn apartment or tack room with full plumbing, not just a wash rack.
3. Rheem RTEX-13 — Best Electric for a Barn With a Sub-Panel
Rheem RTEX-13 13 kW Electric Tankless Water Heater
- The right call if your barn already has a sub-panel with real amperage and you'd rather not manage a propane tank, refills, or outdoor-only winterizing.
- Up to 3.17 GPM per Rheem's spec — in the same range as the two propane picks above, enough for one fixture or a warm-climate wash-rack hose, per Rheem's own point-of-use guidance.
- Needs its own dedicated circuit and 54A of panel capacity — get an electrician to confirm your barn's sub-panel has the headroom before you buy, since many older barn services don't.
Electric only makes sense for a barn when the electrical work is already done — a sub-panel with spare 240V capacity turns the RTEX-13 into a simple point-of-use install with no propane logistics at all. The tradeoff is the same freeze-protection dependency on power described above: if your barn’s electrical service is itself the thing most likely to go out in a storm, an electric unit doesn’t solve that problem the way the battery-only propane picks do. See our full point-of-use water heater guide for the 120V mini-tank alternative if 3.17 GPM is more than your single wash sink actually needs, and our full Rheem lineup if you need more flow than one point-of-use unit can deliver.
How to choose by what your barn actually has
- Propane tank, a hose bib, and no reliable backed-up power: the Camplux BW264-N — zero electrical dependency, lowest cost of the three.
- Same setup, but washing several horses or fixtures back to back: the Eccotemp L10 — more GPM and BTU on the same battery-only design.
- Existing sub-panel with real 240V capacity, no interest in propane: the Rheem RTEX-13 — but confirm your electrician can clear 54A before you order it.
- Full plumbing to a barn apartment or tack room, not just a wash rack: size up to a whole-home unit and read our tankless water heater sizing guide first — and if it’s a permanently plumbed install, ask about Rinnai’s mechanical Freeze Protection Drain-Down Kit as backup redundancy rather than relying on the electronic sensor alone.
- Before you buy anything: check how reliable your property’s power actually is in a winter storm — that answer matters more to a barn install than it does to a house.
The bottom line
For most barns, the Camplux BW264-N is the best tankless water heater — 2.64 GPM, 68,000 BTU, and zero dependency on the power that a winter storm is most likely to take out first in a detached outbuilding. Washing more than one horse at a time, the Eccotemp L10 steps up to 3.0 GPM on the same battery-only design. Already have a sub-panel with spare capacity and no interest in propane? The Rheem RTEX-13 covers a single wash-rack fixture at up to 3.17 GPM. Whichever you pick, remember that a whole-home unit’s “freeze protection down to -30°F” claim — per Rinnai’s own guidance — assumes the power stays on, which is a weaker bet in a barn than in a house.