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Here is the awkward thing about this category: a conventional gas tank water heater is one of the few home appliances we would tell you not to buy online. It is a 150-pound freight item that arrives on a pallet, it is frequently damaged in transit, returns are painful, and every unit needs correct venting, a permit in most jurisdictions and — in most places — a licensed gas fitter to connect it. Local plumbing suppliers and big-box stores handle the delivery, the haul-away and the install as one transaction, and the price difference rarely justifies the risk.
What gas does make sense to buy online is tankless. Those are wall-mounted units in the 40-to-70-pound range that ship by parcel, and they are where the interesting engineering in gas water heating currently sits. So this page does two jobs: it ranks the gas tankless units with a credible ownership record, and it tells you honestly what to look for if a tank heater is the right answer for your house.
Top Picks at a Glance
Gas tank or gas tankless?
| Gas tank | Gas tankless | |
|---|---|---|
| Typical unit price | $600–$1,400 | $700–$1,800 |
| Typical installed price | $1,200–$2,500 | $2,500–$5,500 |
| Expected life | 10–12 years | ~20 years |
| Burner input | ~36,000–50,000 BTU/hr | 120,000–199,000 BTU/hr |
| Gas line | Usually the existing 1/2-inch | Frequently needs 3/4-inch or 1-inch |
| Venting | Existing flue often reusable | New stainless or concentric vent |
| Hot water | Runs out, then recovers | Continuous, limited by flow |
| Footprint | A closet corner | A wall |
| Annual maintenance | Flush the tank | Descale the heat exchanger |
The row that decides most real projects is gas line. A 40-gallon gas tank burns around 40,000 BTU per hour; a whole-house tankless unit burns four to five times that. A half-inch line sized for the tank very often cannot deliver enough gas at pressure, and upgrading the run from the meter — plus the new venting a tankless unit requires — routinely costs more than the heater. Get that assessed before you fall in love with a model.
Our #1 Pick: Rheem RTG-70DVLN-3
At 180,000 BTU per hour and a rated 7.0 GPM, the RTG-70DVLN-3 sits exactly where most households need it. Run the temperature-rise arithmetic and the case is clear: output flow equals BTU per hour divided by 500 times the rise in °F, so at a 70-degree rise — a northern winter, groundwater around 40°F, a 110°F shower — this unit still delivers roughly 5 gallons per minute. Two showers at once, in February. No electric tankless an ordinary residential panel can feed comes close to that.
Rheem's advantage over the newer entrants is not the hardware so much as what surrounds it: the widest parts and service network in American water heating. On an appliance expected to run for two decades, the question that matters in year nine is whether anyone can get a control board, and with Rheem the answer is yes almost anywhere.
The honest limitations are the category's, not the unit's. It is non-condensing, so it needs a Category III stainless vent rather than PVC and its efficiency sits around the low 0.80s UEF rather than the 0.90s a condensing unit reaches. It needs a gas line that can actually feed 180,000 BTU. And it needs annual descaling through isolation valves, which should be fitted at installation because retrofitting them is awkward. None of this is homeowner work: gas connections and venting are licensed, permitted work in most jurisdictions.
Check price on Amazon → (paid link)
The Ranked Field
Best for a typical three-bath home replacing a gas tank with tankless
- 7.0 GPM maximum, 180,000 BTU per hour
- Direct-vent indoor installation with a concentric vent kit
- Low-NOx burner meeting stricter regional air quality rules
- Freeze protection rated to −30°F and a digital remote control
Why buy it: the balance point of the gas tankless range — enough output for two simultaneous showers in a cold climate, from a brand with the widest parts and service network in America.
Best for large homes, four or more bathrooms, or a soaking tub that never fills fast enough
- 199,000 BTU per hour, 9.8 GPM maximum flow
- Indoor installation with a stainless Category III vent
- Commercial-grade heat exchanger with a 15-year exchanger warranty
- Compatible with recirculation controls for instant hot water
Why buy it: Rinnai are the longest-established tankless brand in the US market and the one plumbers most often install, which matters when you need a control board in year nine.
Best for warm and mild climates where mounting outside removes the venting problem entirely
- 8.4 GPM maximum, 180,000 BTU per hour
- Outdoor wall mount — no vent pipe, no combustion air calculation
- Built-in freeze protection down to −30°F with power connected
- Low-NOx burner and digital remote control
Why buy it: venting is the most expensive and most restrictive part of a gas tankless install, and hanging the unit outside deletes it — which is why outdoor models dominate in the South and West.
Best for maximum flow per dollar, if you are comfortable with a newer brand
- 199,000 BTU per hour with a rated maximum of 10.3 GPM
- Indoor installation with WiFi and app temperature control
- Digital display with error codes and a wired remote
- Stainless heat exchanger and overheat protection
Why buy it: top-tier output at roughly half the price of the established brands — the trade-off is a shorter track record and a smaller service network, which on a fifteen-year appliance is a real consideration.
Best for apartments, one-bathroom homes and additions
- 100,000 BTU per hour, 4.3 GPM maximum flow
- Compact indoor unit suited to a small utility space
- Digital display and constant-temperature control
- Lower gas demand than a 199,000 BTU unit, so the existing line may suffice
Why buy it: the gas-line question is the hidden cost in this category, and a 100,000 BTU unit is far more likely to run on the pipe you already have than a 199,000 BTU one.
Best for cabins, RVs, outdoor showers and washing the dog
- 1.32 GPM from a standard propane tank, 2 D-cell batteries for ignition
- Runs on 20-PSI regulated propane with a garden hose inlet
- Weighs around 12 lb with a carry handle
- Outdoor use only — no indoor installation under any circumstances
Why buy it: the only unit here you can carry, and the standard answer for an off-grid cabin or an outdoor shower where plumbing anything permanent is not on the table.
Quick Comparison
| Product | Best for | Rating | Price | Buy |
|---|---|---|---|---|
| Rheem RTG-70DVLN-3 High Efficiency Non-Condensing Indoor Tankless Natural Gas Water Heater, 7.0 GPM | Best Overall | — | Check (paid link) | |
| Rinnai RE199iN Non-Condensing Natural Gas Tankless Water Heater, 199,000 BTU, 9.8 GPM, Indoor | Best High Output | — | Check (paid link) | |
| Rheem RTG-84XLN-3 High Efficiency Non-Condensing Outdoor Tankless Natural Gas Water Heater, 8.4 GPM | Best Outdoor Install | — | Check (paid link) | |
| MIZUDO 199,000 BTU Natural Gas Tankless Water Heater, Max 10.3 GPM, Indoor, Non-Condensing | Best Value High Output | — | Check (paid link) | |
| Ranein Natural Gas Tankless Water Heater, Indoor, Max 4.3 GPM, 100,000 BTU | Best Small Gas Tankless | — | Check (paid link) | |
| Camplux 5L Portable Tankless Water Heater, 1.32 GPM, Outdoor Propane for Camping, RV and Off-Grid | Best Portable | — | Check (paid link) |
If a gas tank heater is the right answer, buy it on these specs
For a lot of houses it is the right answer — the venting exists, the gas line is sized for it, and a like-for-like replacement is a morning's work for a plumber. Buy it locally, and shop these four things rather than the price sticker.
- First Hour Rating, not gallons. FHR is how much hot water the unit actually delivers in the busiest hour, combining storage volume with recovery rate. Because gas recovers so much faster than electric, a 40-gallon gas heater frequently has a higher FHR than a 50-gallon electric one. Estimate your peak hour at roughly 20 gallons per shower, 10 for a dishwasher cycle and 7 for a sink shave, then buy an FHR that covers it. Our page on what size water heater you need works through the arithmetic.
- Venting type. Atmospheric (natural draft) units vent up an existing flue by buoyancy and are the cheapest to replace like-for-like. Power vent units use a blower and can vent horizontally through a wall, which is what you need when there is no usable chimney. Direct vent units draw combustion air from outside — the right choice in a tight, well-sealed house. You cannot freely swap between these categories without vent work.
- UEF, the efficiency figure. Uniform Energy Factor replaced the old Energy Factor rating in 2017. Standard atmospheric gas tanks land around 0.58 to 0.64; power vent models reach the high 0.60s to low 0.70s; condensing gas tanks exceed 0.80. Higher UEF costs more up front and returns it slowly — ENERGY STAR's water heater guidance is the neutral place to compare.
- Warranty length as a proxy for build. Six, nine and twelve-year versions of the same heater usually differ in anode rod mass and tank lining rather than in anything you can see. The longer-warranty model is generally the better-built tank, not just the better-insured one.
One more thing worth knowing: all residential gas storage water heaters sold in the US have been required to be flammable vapor ignition resistant since the mid-2000s, which is why a modern unit has a sealed combustion chamber and a flame arrestor plate at the base. It is also why a heater installed in a garage collects lint and dust at the intake screen and eventually starves for air — that screen needs cleaning, and a heater that keeps shutting down in a dusty garage is usually telling you exactly that.
How We Rank
We never buy or install these units. For gas water heaters the ranking priorities are: real output at realistic temperature rise rather than the best-case GPM on the carton; installability, meaning gas line demand and venting requirements, because those decide the true cost; parts and service availability over a twenty-year horizon, weighted heavily; and aggregated owner reports, read with the caveat that this category has a genuinely thinner review record than most consumer products, because gas water heaters are contractor purchases. Ratings come from verified Amazon listing data and refresh automatically. Prices were checked at the time of writing. Full method: how we rank.
The Field, Reviewed
1. Rheem RTG-70DVLN-3 — Best Overall
Covered above. Owners praise: genuinely endless hot water, quiet operation for a gas unit, the digital remote, and the reassurance of Rheem's service network. Owners gripe about: installation cost — venting and gas line together frequently exceed the price of the heater — and the annual descaling requirement that tank owners never had to think about. Check price (paid link).
2. Rinnai RE199iN — Best High Output
Nearly 200,000 BTU and a rated 9.8 GPM, which is genuine large-home capability: three showers in a warm climate, two plus a dishwasher anywhere. Rinnai have been in the US tankless market longer than anyone and are the brand plumbers install most often, which matters for parts a decade out.
Owners praise: output, build quality, the long heat-exchanger warranty, and compatibility with recirculation controls that eliminate the wait at distant fixtures. Owners gripe about: price, a gas line demand that very often forces an upgrade, and the Category III stainless venting a non-condensing unit requires. Check price (paid link).
3. Rheem RTG-84XLN-3 — Best Outdoor Install
The same engineering as our top pick with the single most expensive problem removed. Mounted on an exterior wall there is no vent pipe, no combustion-air calculation and no penetration through a finished ceiling — which is why outdoor tankless dominates in the South and West. Freeze protection is rated to −30°F, but it depends on the unit having power, so a winter outage in a genuinely cold region is a real risk.
Owners praise: a dramatically simpler and cheaper installation, 8.4 GPM of output, and reclaiming the indoor space entirely. Owners gripe about: freeze anxiety in cold climates, and a remote control that has to be run inside. Check price (paid link).
4. MIZUDO 199,000 BTU — Best Value High Output
Top-tier output at roughly half the price of the established brands, with WiFi and app control that the majors charge extra for. The honest counterweight is track record: this is a newer entrant, and on a fifteen-to-twenty-year appliance the question of who supplies a control board in year twelve is not academic.
Owners praise: the output for the money, the app control, and a clear digital display with usable error codes. Owners gripe about: documentation that reads as translated, and support that is a phone number rather than a national network. Check price (paid link).
5. Ranein 4.3 GPM — Best Small Gas Tankless
At 100,000 BTU this is roughly half the gas demand of the big units, and that is the point: a smaller burner is far more likely to run on the gas line already in the house. For a one-bathroom home, an apartment or an addition, 4.3 GPM is enough, and avoiding a gas line upgrade can halve the project cost.
Owners praise: the price, the compact body, and an install that did not require re-piping. Owners gripe about: output that is genuinely limited if two fixtures run at once, and the same newer-brand support caveat. Check price (paid link).
6. Camplux 5L Portable — Best Portable
A different animal entirely: a 12-pound propane heater with a garden hose inlet and battery ignition, for cabins, RVs, outdoor showers and washing dogs. It is outdoor use only — running an unvented propane appliance indoors is a carbon monoxide hazard, without exception.
Owners praise: genuinely hot water anywhere there is propane and a hose, quick setup, and the price. Owners gripe about: the burner cutting out in wind, the need for a proper 20-PSI regulator rather than a low-pressure camping one, and modest 1.32 GPM flow. Check price (paid link).
What Owners Actually Complain About
The install, not the unit. Overwhelmingly the top complaint in gas tankless. Venting, gas line sizing and permits together frequently cost more than the heater, and buyers who priced only the box feel misled.
The cold water sandwich. Turn hot water off and back on within a minute and a slug of cold water arrives between two hot ones. It is inherent to tankless, mitigated by a recirculation loop, and never fully eliminated.
Scale. The leading cause of premature failure. Hard water deposits on the heat exchanger, output drops, error codes appear. Annual descaling prevents it, and isolation valves make it possible — insist on them. If your water is hard, read how to test water hardness first.
Freight damage on tank heaters. The reason this page opens the way it does. A dented flue collar or a damaged jacket on a pallet-delivered tank is a genuinely miserable return.
Venting confusion. Buyers replacing an atmospheric tank with a power vent model, or a non-condensing tankless unit with PVC pipe, discover mid-project that vent categories are not interchangeable. Confirm what your installer intends to use before the old unit comes out.
Safety and permits
Gas appliances are the one area of home plumbing where the DIY answer is simply no. Gas connections, venting and combustion air are licensed, permitted work in most US jurisdictions, and the failure mode is carbon monoxide rather than a puddle. A working CO alarm on every level of the home is not optional in a house with gas appliances.
Permits and inspection requirements are set locally — check with your city or county building department before you buy, because some jurisdictions also require seismic strapping, an expansion tank, a drain pan with a piped discharge, or a specific T&P discharge termination. Our page on whether you need a permit to replace a water heater covers what is typically involved.
The Verdict
If you are going tankless on gas, the Rheem RTG-70DVLN-3 is the sensible whole-house choice and the Rinnai RE199iN is the one for a large house or a slow-filling tub. Mild climate? Hang the Rheem RTG-84XLN-3 outside and delete the venting cost. If the gas line is the constraint — and it usually is — the smaller Ranein 4.3 GPM unit may be the only realistic option without re-piping. And if what you actually need is a conventional gas tank, buy it from a local supplier with delivery, haul-away and a licensed install included, and shop it on First Hour Rating rather than gallons. Check price on Amazon → (paid link)
More from this hub: DIY plumbing · best tankless water heater · what size water heater do I need · running costs · how to flush a water heater · how we rank.