Heating & appliances
Propane tankless water heaters
A propane tankless water heater lights its burner only while hot water is flowing, so it skips the standby loss of a storage tank and will not run out partway through a shower. Size it by how many gallons per minute your household draws at once and by the winter temperature rise, and have the gas line, venting and electrical supply checked before the unit is ordered.
Updated · American River Gas office, Newcastle
What happens when you open the hot tap
Cold water starts moving into the heater, a flow sensor sees it and fires the burner, and the water picks up heat as it passes around the heat exchanger. It leaves at the temperature you set. Exhaust goes out through a dedicated sealed vent. When you close the tap, the burner shuts off. That on-demand cycle is described in ENERGY STAR's guide to whole-home gas tankless heaters.
Because nothing sits in a tank staying hot all day, there is no fuel spent keeping stored water warm. ENERGY STAR also lists practical perks: the units are small and wall-mounted, outdoor models free up indoor space, and there is no tank to leak and flood a garage.
Sizing by gallons per minute
Storage heaters are sized by gallons in the tank. Tankless heaters are sized by how much hot water they can produce per minute (GPM). Add up the fixtures your household really runs at the same time. ENERGY STAR gives these average flows as a starting point:
- Shower or bathtub: about 2.5 GPM
- Clothes washer: about 3.3 GPM
- Kitchen or bathroom sink: about 2.2 GPM
- Dishwasher: about 1.3 GPM
Why winter is the month that matters
Using those averages, two showers and a dishwasher at once come to roughly 6.3 GPM. The heater's real output, though, depends on how many degrees it has to raise the water. Incoming water is colder in winter, so the same heater delivers fewer gallons per minute in January than in July. Homes on wells should ask the installer to use a realistic winter inlet temperature. A plumber should confirm the final size, as ENERGY STAR advises, and larger homes sometimes use two units side by side.
Condensing or standard?
ENERGY STAR certified gas tankless heaters add a second heat exchanger that pulls extra heat from the exhaust, and ENERGY STAR says they use 9 percent less energy than a conventional tankless model. Cooling the exhaust that far makes water condense out, so these condensing units vent through PVC pipe and need a drain for the condensate. A standard (non-condensing) unit uses a different, heat-rated vent. Where the heater can go, and how the vent and drain will run, often decides which type fits your house.
What a tankless heater asks of your propane system
A whole-home tankless heater only burns while water flows, but when it runs it wants a lot of gas at once. That puts the spotlight on the gas line size and the regulator, and in a home that also runs a furnace, range and fireplace it can change what tank size makes sense. ENERGY STAR tells buyers to have the installer confirm the existing gas line is big enough, that power is available near the heater, and how exhaust will be vented.
Call us before the plumber orders the unit. We can look at your tank, regulator and line and tell you whether anything needs to change. The new connection gets a leak test, and the heater needs its own shut-off valve within 6 feet. Propane is heavier than air, so California's Mechanical Code limits propane appliances in pits, basements and similar low spots, as Placer County's appliance handout explains.
Power, freezing and outages
Tankless heaters use electricity for controls, ignition and, on many models, a combustion fan, so they stop during a power outage. If hot water during a PG&E shutoff matters to you, ask about a storage model with a standing pilot, which can keep heating without electricity. For an outdoor-mounted unit, read how the manual protects it from freezing on a cold night and whether that protection depends on power.
Living with one
ENERGY STAR puts the life expectancy of a tankless unit at about 20 years, longer than a typical storage tank. The heat exchanger does need care. Hard water leaves scale, so follow the manufacturer's descaling schedule, and have a qualified technician check the burner and venting. Some homes add a recirculation setup so hot water reaches far bathrooms sooner.
Plan ahead if you can. ENERGY STAR notes an installer may need time to order the right model and the job can take longer than a like-for-like tank swap, so shopping before the old heater fails gives you room to choose. Check the ENERGY STAR rebate finder for current incentives too.
Questions
Straight answers
What size propane tankless water heater do I need?
Add the flow of fixtures you run at once, such as about 2.5 GPM per shower, then size for your coldest incoming water. A plumber should confirm the final choice.
Do propane tankless water heaters work without power?
Generally no. Their controls, ignition and fans need electricity. If you want hot water during an outage, a storage model with a standing pilot may suit you better.
Will a tankless water heater need a bigger gas line?
Often. A whole-home unit has a large burner. Have the line and regulator checked before you buy, and call us to review your tank and system.
Does a tankless heater use less propane than a storage heater?
It avoids the fuel a storage tank spends keeping water hot all day, so it usually uses less for the same hot water. How much less depends on your household and the models compared.
Can I convert a natural gas tankless heater to propane?
Only if the maker offers a propane conversion for that model, installed by a qualified technician and followed by a leak test. Many models are also sold in a propane version from the factory.
Related
Keep reading
Sources: ENERGY STAR: whole-home tankless gas water heaters (buying guidance and GPM averages) (opens in a new tab) · ENERGY STAR: how whole-home gas tankless water heaters work (opens in a new tab) · ENERGY STAR: tankless water heater savings and benefits (opens in a new tab) · Placer County Building Services: propane appliances handout (California Mechanical Code 303.7.1) (opens in a new tab)
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