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Propane Tankless Water Heaters
Quick answer: Yes — many tankless models run on propane (LP) as dedicated LP units or with a manufacturer-approved conversion kit. Sizing math matches natural gas (GPM × rise). Propane holds about 91,500 BTU per gallon; a 180k BTU/h unit uses about 2 gallons per firing hour. A licensed gas fitter confirms supply.
Context: tankless without a gas main
Rural and off-grid homes often have no natural gas line but do have a propane tank. Propane tankless units bring the same on-demand hot water and high flow as natural gas models. The differences are fuel cost, tank and regulator capacity and the need for the correct LP-rated equipment.
Terms
- LP / propane model: a unit built or factory-configured for propane.
- Conversion kit: manufacturer-approved parts to convert a unit between fuels, installed by a licensed pro.
- Regulator: controls propane pressure from the tank; must handle the unit's full BTU/h.
- Vaporisation rate: how fast a propane tank turns liquid into gas; small tanks in cold weather may not keep up.
Propane vs natural gas (example)
| Factor | Propane | Natural gas |
|---|---|---|
| Energy content | ~91,500 BTU per gallon | ~100,000 BTU per therm |
| Example fuel price | $2.00–$3.50 per gallon | $1.00–$2.00 per therm |
| Example cost per million BTU | $22–$38 | $10–$20 |
| Supply | On-site tank, refills | Utility line |
| Unit sizing | Same GPM × rise math | Same |
Process: planning a propane install
- Size with the tankless size calculator and BTU calculator.
2. Buy the LP version or an approved conversion — never mix fuels.
3. Ask your propane supplier and a licensed gas fitter whether the tank, vaporisation rate and regulator support the unit's full BTU/h alongside other appliances.
4. Plan venting and location — see indoor vs outdoor.
5. Estimate yearly fuel with the worked example below.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 180,000 BTU/h unit, average 20 minutes of full-equivalent firing per day, propane at $2.75/gallon.
- Per day: 180,000 × (20 ÷ 60) = 60,000 BTU ÷ 91,500 ≈ 0.65 gallons.
- Per year: 0.65 × 365 ≈ 240 gallons ≈ $660.
- Same energy on natural gas at $1.50/therm: 21.9 million BTU ≈ 219 therms ≈ $330.
- Compared with a propane tank heater with standby loss, a tankless might save roughly 10–25% on fuel in this example.
Tank size considerations
Small 100-pound cylinders often cannot vaporise fast enough for a large tankless unit, especially in cold weather. Larger 250–500 gallon tanks are more common for whole-home tankless. Your supplier and gas fitter decide.
Mistakes to avoid
- Installing a natural gas unit on propane without the approved conversion.
- Undersizing the regulator or tank.
- Ignoring higher fuel cost when estimating savings.
FAQ
Is propane tankless efficient?
Yes; condensing LP models reach about 0.90–0.97 efficiency, avoiding standby loss.
Can I convert later to natural gas?
Some models allow approved conversion kits; a licensed pro must do it.
Does propane affect GPM?
No — the same BTU/h gives the same GPM at a given rise.
Will cold weather affect supply?
It can reduce vaporisation from small tanks; plan tank size accordingly.
Safety and code reminders
Gas, venting, combustion air, condensate disposal and high-amperage electrical work all carry real safety risks, including carbon monoxide, fire, scalding and shock. They are also governed by local code and permits that differ between towns and provinces or states. Treat every step on this page as preparation for a professional visit, not as instructions to do the work yourself. Keep the manufacturer's manual for your exact model, set water temperature with scald risk in mind (120°F is a common household target), and stop and call a licensed professional whenever something is unclear.
Quick reference: typical fixture flow rates
These example flow rates help you translate everyday use into the GPM numbers used throughout this site. Check the rating stamped on your own fixtures, as older fixtures often run higher.
| Fixture | Example hot-water flow |
|---|---|
| Low-flow showerhead | 1.5–1.8 GPM |
| Standard showerhead | 2.0–2.5 GPM |
| Bathroom faucet | 0.5–1.2 GPM |
| Kitchen faucet | 1.0–1.8 GPM |
| Dishwasher | 0.8–1.5 GPM |
| Washing machine (warm) | 1.0–2.0 GPM |
| Bathtub fill | 2.0–4.0 GPM |
Add only the fixtures that genuinely run at the same time. Running the dishwasher or laundry outside shower hours is the simplest way to stay within a unit's capacity.
Questions to ask a licensed installer
Bring these questions to every quote so you can compare them fairly. Good installers welcome them, and the answers often reveal hidden costs before work starts.
- What peak GPM and temperature rise did you size this unit for, and what inlet water temperature did you assume for winter?
- Is my existing gas line, meter or electrical panel large enough, and if not, what exactly needs upgrading and what does that line item cost?
- What venting route will you use, how long is it, and does it meet the manufacturer's instructions and local code?
- Does the quote include a permit, isolation (service) valves for future flushing, a condensate drain if needed, and removal of the old heater?
- What are the labour warranty and the manufacturer's heat-exchanger and parts warranty terms, and do they require registration or yearly professional service?
- How long will the install take, and will there be a period without hot water?
How to read the numbers on this site
Every figure on TanklessMath is a planning estimate. Ranges reflect typical North American examples as of 2026-10-29 and will differ with your region, home, fuel prices and installer. Equipment ratings vary by model, so always check the specification sheet for the exact unit you are considering. When our example and a licensed installer disagree, trust the installer who has seen your home.
Next steps
Write down your peak fixtures, coldest incoming water temperature, fuel type and possible locations, then ask at least two licensed installers to confirm sizing, venting, gas or electrical capacity, permits and local code. Compare written quotes line by line so the unit, labour, materials and upgrades are separated. Questions about this site: hello@charlandandco.com.
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