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Best Tankless Water Heaters, Compared on What Your Permit Will Need
Electric and gas tankless water heaters compared on the paperwork behind the permit: circuits and panel size, gas line and venting, safety certification, and who the maker says must install it.
Updated Oct 5, 2026
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Replacing a water heater usually needs a permit, and switching from a tank to tankless can widen it. An electric tankless unit often needs new high-amp circuits and sometimes a bigger electrical service. A gas unit may need a larger gas line and a new vent. Those hookups, not the heater itself, decide how much work and inspection the job involves.
Key takeaways
- Check the rule for your address before you order. Water heater work is permitted in most places.
- For electric tankless, compare the maker's breaker and main-service sizes with your panel first.
- For indoor gas tankless, the vent is new work. Outdoor units skip the vent pipe.
- Most makers say a licensed electrician, plumber or gas installer must do the install, or the warranty can be void.
How we compare tankless water heaters
We did not test these heaters. We read each maker's spec sheets and installation manuals, checked the safety certifications they name, and checked that each Amazon listing is sold by Amazon itself.
Our picks
- 1Best whole-house electric
Stiebel Eltron Tempra 24 Trend
Model Tempra 24 Trend
Permit paperwork: CompleteA whole-house electric tankless heater with the most complete paperwork here: flow at stated temperature rises, breaker and wire sizes, the minimum main service, and a manual that names who must install it.
Why we picked it: Stiebel publishes everything a permit needs in one tech sheet, including a 150-amp minimum main service, and the manual names a licensed electrician and plumber.
Permit paperwork
- Yes:Safety certification named (UL 499, CSA C22.2 No. 88)
- Yes:Installation manual published
- Yes:Spec sheet published
- Yes:Electrical or gas and vent requirements published (Breakers, wire and service size)
- Yes:Flow published at a stated temperature rise
- Yes:Maker says who must install it (Licensed electrician and plumber)
Specs
- Type
- Electric, whole house, indoor
- Flow
- 3.0 GPM at a 54°F rise; 2.25 GPM at 73°F (240 V)
- Hookup
- 2 x 50 A double-pole breakers, 2 x 8/2 AWG copper
- Service
- 150 A main service minimum (maker)
- Warranty
- 7 years leakage, 3 years parts
Maker documents
Check price on AmazonChecked 2026-10-05 - 2Best indoor gas
Rheem RTG-70DVLN-3 Indoor Natural Gas
Model RTG-70DVLN-3
Permit paperwork: CompleteAn indoor natural gas unit for replacing a tank in the same spot. Indoor gas means a new vent, which is the part an inspector looks at closest, and Rheem publishes the vent and gas line limits.
Why we picked it: Rheem publishes the vent length and gas line limits that an indoor install depends on, and flow at three temperature rises.
Permit paperwork
- Partly:Safety certification named (Design-certified mark, no listing number)
- Yes:Installation manual published
- Yes:Spec sheet published
- Yes:Electrical or gas and vent requirements published (Gas line and vent length published)
- Yes:Flow published at a stated temperature rise
- Yes:Maker says who must install it (Qualified installer, service agency or gas supplier)
Specs
- Type
- Natural gas, indoor, direct vent
- Flow
- 7.0 GPM at a 35°F rise; 4.5 GPM at 67°F
- Hookup
- 1/2 in. gas line up to 24 ft where code allows; vent run up to 43 ft
- Warranty
- 15 years heat exchanger, 5 parts, 1 labor
Maker documents
Check price on AmazonChecked 2026-10-05 - 3Best outdoor natural gas
Rheem RTG-84XLN-3 Outdoor Natural Gas
Model RTG-84XLN-3
Permit paperwork: CompleteAn outdoor natural gas unit, so there is no vent pipe to run through the house. That usually makes for a simpler install, though the gas line and water lines still need the right sizes and a permit.
Why we picked it: No vent pipe through the house, the highest flow in this list, and the same complete Rheem paperwork.
Permit paperwork
- Partly:Safety certification named (Design-certified mark, no listing number)
- Yes:Installation manual published
- Yes:Spec sheet published
- Yes:Electrical or gas and vent requirements published (Gas line limits published; no vent needed)
- Yes:Flow published at a stated temperature rise
- Yes:Maker says who must install it (Qualified installer, service agency or gas supplier)
Specs
- Type
- Natural gas, outdoor, no vent pipe
- Flow
- 8.4 GPM at a 35°F rise; 5.1 GPM at 67°F
- Hookup
- 1/2 in. gas line up to 24 ft where code allows
- Warranty
- 15 years heat exchanger, 5 parts, 1 labor
Maker documents
Check price on AmazonChecked 2026-10-05 - 4Best for propane homes
Rheem RTG-70XLP-3 Outdoor Propane
Model RTG-70XLP-3
Permit paperwork: CompleteThe propane version of Rheem's outdoor unit, for homes without natural gas. Propane line sizing and the tank connection are gas work, so plan for a licensed installer.
Why we picked it: The outdoor RTG in a propane version, with the same published flow, gas line and installer requirements.
Permit paperwork
- Partly:Safety certification named (Design-certified mark, no listing number)
- Yes:Installation manual published
- Yes:Spec sheet published
- Yes:Electrical or gas and vent requirements published (Gas line limits published; no vent needed)
- Yes:Flow published at a stated temperature rise
- Yes:Maker says who must install it (Qualified installer, service agency or gas supplier)
Specs
- Type
- Propane, outdoor, no vent pipe
- Flow
- 7.0 GPM at a 35°F rise; 4.5 GPM at 67°F
- Hookup
- 1/2 in. gas line up to 24 ft where code allows
- Warranty
- 15 years heat exchanger, 5 parts, 1 labor
Maker documents
Check price on AmazonChecked 2026-10-05 - 5Best point-of-use electric
Rheem RTEX-11 Point-of-Use Electric
Model RTEX-11
Permit paperwork: LimitedA small electric unit for one or two fixtures, such as a far bathroom or a kitchen. It still needs its own 50-amp circuit, which is electrical work that usually needs a permit.
Why we picked it: A single 50-amp circuit and a 100-amp panel are enough, which makes it a practical way to add hot water at one far fixture.
Permit paperwork
- Not found, ask the maker:Safety certification named (not found, ask the maker)
- Yes:Installation manual published
- Yes:Spec sheet published
- Yes:Electrical or gas and vent requirements published (Breaker, wire and panel size)
- Partly:Flow published at a stated temperature rise (Maximum flow, no stated rise)
- Not found, ask the maker:Maker says who must install it (not found, ask the maker)
Specs
- Type
- Electric, point of use, indoor
- Flow
- Up to 2.68 GPM, depending on incoming water temperature
- Hookup
- 1 x 50 A double-pole breaker, 6 AWG copper (46 A at 240 V)
- Service
- 100 A household panel (maker recommendation)
- Warranty
- 5 years heating chamber, 1 year parts
Maker documents
Check price on AmazonChecked 2026-10-05
Side by side
| Product | Paperwork | Type | Flow | Hookup | Service | Warranty |
|---|---|---|---|---|---|---|
| Stiebel Eltron Tempra 24 Trend | Complete | Electric, whole house, indoor | 3.0 GPM at a 54°F rise; 2.25 GPM at 73°F (240 V) | 2 x 50 A double-pole breakers, 2 x 8/2 AWG copper | 150 A main service minimum (maker) | 7 years leakage, 3 years parts |
| Rheem RTG-70DVLN-3 Indoor Natural Gas | Complete | Natural gas, indoor, direct vent | 7.0 GPM at a 35°F rise; 4.5 GPM at 67°F | 1/2 in. gas line up to 24 ft where code allows; vent run up to 43 ft | Does not apply | 15 years heat exchanger, 5 parts, 1 labor |
| Rheem RTG-84XLN-3 Outdoor Natural Gas | Complete | Natural gas, outdoor, no vent pipe | 8.4 GPM at a 35°F rise; 5.1 GPM at 67°F | 1/2 in. gas line up to 24 ft where code allows | Does not apply | 15 years heat exchanger, 5 parts, 1 labor |
| Rheem RTG-70XLP-3 Outdoor Propane | Complete | Propane, outdoor, no vent pipe | 7.0 GPM at a 35°F rise; 4.5 GPM at 67°F | 1/2 in. gas line up to 24 ft where code allows | Does not apply | 15 years heat exchanger, 5 parts, 1 labor |
| Rheem RTEX-11 Point-of-Use Electric | Limited | Electric, point of use, indoor | Up to 2.68 GPM, depending on incoming water temperature | 1 x 50 A double-pole breaker, 6 AWG copper (46 A at 240 V) | 100 A household panel (maker recommendation) | 5 years heating chamber, 1 year parts |
Electric tankless: check your panel first
Whole-house electric tankless heaters draw a lot of current. Stiebel's own tech sheet, for example, recommends at least a 150-amp main service for the Tempra 24, 200 amps for the larger Tempra 29, and 300 amps for the Tempra 36. If your panel is smaller, the job may include a service upgrade, which is its own permitted electrical work. Point-of-use units need far less.
Gas tankless: the gas line and the vent
Tankless gas heaters burn more gas at once than most tanks, so the existing gas line may be too small. Rheem, for example, says a half-inch line works for its RTG models only up to 24 feet, and only where local code allows. Indoor units also need a vent run to the outside, which the inspector checks. Outdoor units avoid the vent but still need the gas and water connections done to code.
Indoor or outdoor?
Outdoor gas units suit warm climates and save the vent work. In freezing climates, ask your installer about freeze protection and where an outdoor unit can sit. Indoor units keep everything inside but add the vent.
What to hand your installer
Send the model number, spec sheet and installation manual before they quote. They need the breaker and panel sizes, or the gas input and vent length, to price the job and pull the right permit.
Also considered
Products we looked at and left out, as of Oct 5, 2026. No links, because we would not recommend buying them through us.
Rinnai V53DeN and V53DeP outdoor gas
Their Amazon listings were sold by a reseller (eFaucets), not Rinnai or Amazon.
Stiebel Eltron Tempra 29 Plus
Its Amazon listing was sold by a reseller (Big Frog Supply), not Stiebel or Amazon. It also calls for a 200-amp main service.
Before you order, check your address
Permit rules change from one city to the next. The free check tells you what your building department requires, the documents to prepare and who to call.
Check my projectFrequently asked questions
- Do I need a permit to install a tankless water heater?
- In most places, yes. Water heater replacement is usually permitted plumbing work, and tankless conversions often add electrical or gas and vent work. Check your address for the local rule.
- Will a tankless water heater need a bigger electrical panel?
- Whole-house electric models often do. Compare the maker's recommended main service, such as 150 amps for the Stiebel Tempra 24, with your panel before you buy.
- Can I reuse my old gas line and vent?
- Sometimes not. Tankless gas heaters can need a larger gas line, and a tank's vent is usually not approved for a tankless unit. Your installer checks both against the maker's instructions and local code.
- Did you test these water heaters?
- No. We compared what each maker publishes in its spec sheets and manuals, and checked that each Amazon listing is sold by Amazon. Our ratings describe the paperwork, not performance.
- Can I install a tankless water heater myself?
- Check both your local rules and the maker's terms. Stiebel says its heaters must be installed by a licensed electrician and plumber, and Rheem says installation must be done by a qualified installer, service agency or gas supplier.
- Why are the prices not listed?
- Prices change often, so the buttons take you to Amazon for the current price. PermitRoadmap earns a commission on qualifying purchases, which does not change our ratings or the permit information.
PermitRoadmap is an independent informational service and is not affiliated with any city, county, state agency, or permitting authority. Results are informational and do not replace confirming requirements with the local permitting authority.