6kW or 10kW? Choosing Between Two Portable Gas Water Heaters
Buying Guides & Technical Comparisons Series | SEFFY Mobile Water Systems
Two portable gas water heaters sit on the shelf. Same body shape, same self-priming pump, same four-gas compatibility, same battery system. One is rated 6kW; the other is rated 10kW.
A camper takes the smaller one to a summer lake and is completely satisfied for a week. Another camper takes the same smaller unit up to a mountain stream in October, where the water comes out of the ground at around 6°C, and ends up with a lukewarm trickle he cannot call a shower.
Neither of them was lied to. The difference between those two trips is not the campsite and it is not the brand. It is a single number: the temperature rise the water needs.
This guide shows you how to work that number out for your own trips, and which of the two portable models handles it.
The Only Number That Matters: Temperature Rise
Heating water obeys one equation:
P = ṁ × c × ΔT
where P is heating power in watts, ṁ is mass flow in kg/s, c is the specific heat of water (4,186 J/kg·K), and ΔT is the temperature rise — outlet temperature minus inlet temperature.
To choose a model, you need two temperatures and one subtraction.
- Inlet: what the water is when it reaches you. A sun-warmed lake in summer might be 20°C. A mountain stream in October can be 5–8°C.
- Outlet: what you want at the shower head. Most people find 38–42°C comfortable.
Then ΔT = outlet − inlet:
- Summer lake: 20°C → 40°C = ΔT 20K
- Autumn stream: 6°C → 40°C = ΔT 34K
Now here is what the two models are built to deliver.
Flue Type — rated 6kW, hot water capacity 3 L/min at Δt=25K, maximum temperature rise 25K. Designed for warm inlet water and a light, compact travel pack.
Thermostatic — rated 10kW, hot water capacity 6 L/min at Δt=25K, maximum temperature rise 55K. Designed for cold inlet water and a full-flow hot shower.
Run the two trips through those numbers:
- The summer trip (ΔT 20K) sits inside the Flue Type's 25K ceiling. At roughly 3 L/min the shower is comfortable, and the smaller unit burns less gas doing it. The 6kW model is enough.
- The autumn trip (ΔT 34K) does not fit. The Flue Type tops out far below a comfortable shower temperature, so the water arrives warm at best. The Thermostatic's 55K ceiling covers the same 34K with room to spare, and it still holds its rated output when the air is cold.
That is the entire buying decision in one line: the colder your water source, the more temperature rise you need — and temperature rise is what separates the two models.
Figure 1. Inlet temperature is the number that decides the model. Water drawn straight from a stream in autumn can arrive at 5–8°C, which is what turns a temperature-rise problem into a model-choice problem.
What Else Actually Differs
Gas burn, and therefore how many canisters you carry. The Flue Type consumes a maximum of 360 g/h; the Thermostatic consumes up to 600 g/h. Put differently: a single 450 g butane canister yields roughly 75 minutes of flame on the smaller unit, against about 45 minutes on the larger one. Over a week of warm-water lake camping, that is the difference between roughly three canisters and roughly five.
Weight. 6.8 kg for the Flue Type against 8.5 kg for the Thermostatic. A 1.7 kg gap is trivial in a car boot and very noticeable when you are carrying the unit down to the water and back.
Cold-weather canister behaviour. The Thermostatic carries a patented canister anti-frost system that uses combustion waste heat to warm the gas canister, with exhaust temperature dropping to a safe 45°C. A canister that frosts loses internal pressure, and a propane appliance that loses pressure loses heat output — which is precisely the failure mode the larger unit was engineered to avoid.
Storage and packing. The Flue Type is the all-in-one travel set. Dedicated storage on both sides holds the shower head, the 3-metre shower hose and the 1.5-metre pump, and the unit ships with a 2-in-1 multifunctional water bag that unfolds into a generous 40L water bucket, then packs the machine inside afterwards to become a shoulder bag.
What both models share. Both run the same 25W self-priming DC pump across an applicable water pressure range of 0.025–0.4 MPa, so both draw directly from a jerry can, a drum, a bucket or a stream with no mains pressure and no plumbing. Both use the same 5200mAh lithium pack (about 3.5 hours to a full charge, up to roughly 150 minutes of hot water per charge), the same DC 12V system, and the same 490 × 215 × 315 mm body. Both accept four gas types — propane, LPG, butane and high-mountain blends — and both carry the patented smart starter with 20-minute reignition: switch the shower head off to lather up and the unit stays on standby for up to twenty minutes, then relights the moment you reopen it.
Read the third row first. Everything else in this table is a detail; the maximum temperature rise is the decision.
Four Questions That Settle It
1. What is your inlet water temperature?
Consistently above about 18°C (summer lakes, stored water in the sun) → the 6kW Flue Type is enough.
Below about 15°C (autumn and winter streams, groundwater, altitude) → take the 10kW Thermostatic.
2. Do you want a full 6 L/min shower, or is 3 L/min fine?
6 L/min at a genuine temperature → 10kW. The 6kW unit is rated for 3 L/min and that is where it performs at its best.
3. How many gas canisters are you willing to carry?
Fewer → the 6kW unit's 360 g/h burn stretches each canister by roughly two-thirds.
4. Will you be using it in cold air, where canisters frost?
Yes → the 10kW Thermostatic, whose canister anti-frost system exists for exactly that condition.
Takeaway for Buyers and Dealers
For buyers:
- Estimate your ΔT before you spend anything. It is two temperatures and one subtraction, and it decides the model.
- If your trips are consistently warm-weather and your water source is a lake, a tank or a container sitting in the sun, the 6kW Flue Type is the efficient buy — lighter, and gentler on gas.
- If you camp in autumn or winter, at altitude, or draw from a mountain stream, take the 10kW Thermostatic. Its 55K temperature rise is what keeps the shower hot when the inlet water is not.
- Whichever you choose, the unit needs a charged battery and a filled gas canister before it will start. Both. This is a cordless appliance, not a generator.
- Operate it outdoors or in a thoroughly ventilated exterior area only. Combustion produces carbon monoxide. And note that it is a bathing and cleaning appliance — the water it produces is not for drinking.
For dealers and retail staff:
- Sell by inlet water temperature, not by price point. The wrong model comes back as a "doesn't get hot enough" complaint, which is a fitting problem, not a product fault.
- Ask one question at the counter: what temperature is your water when it comes out of the ground? It separates the two models faster than any specification sheet.
- Lead with gas economy and weight for the 6kW model, and with temperature rise and the anti-frost system for the 10kW model.
- Set the same two expectations for both models — a charged battery and a filled canister — and state plainly that the appliance is for outdoor use and not for drinking water. Accurate expectations are what prevent both returns and unsafe use.
Specifications referenced in this article are for the SEFFY Portable Outdoor Gas Water Heater, models Flue Type and Thermostatic: Flue Type — rated heat load 6kW, hot water capacity 3 L/min at Δt=25K, maximum temperature rise 25K, maximum gas consumption 360 g/h, net/gross weight 6.8/8.3 kg. Thermostatic — rated heat load 10kW, hot water capacity 6 L/min at Δt=25K, maximum temperature rise 55K, maximum gas consumption 600 g/h, net/gross weight 8.5/10 kg. Both models — shower flow rate approximately 3 L/min, applicable water pressure range 0.025–0.4 MPa, 25W self-priming DC pump, DC 12V, 5200mAh lithium battery with up to about 150 minutes of runtime per charge, product dimensions 490 × 215 × 315 mm, compatible with propane, LPG, butane and high-mountain canisters. Heating calculations use the specific heat capacity of water at 4,186 J/kg·K.
