The best slim gas water heater depends on where you need hot water: the Amzgachfktch 6L is best for portable outdoor use, while the ThermoMate CZ422NG and Rheem RTG are better suited to residential, wall-mounted installations. The EXCEL is a low-pressure propane option, and the VEVOR offers indoor on-demand heating with a temperature display. Compare fuel, installation location, flow rate, and available space before choosing.
| Product | Best For | Key Detail |
|---|---|---|
| Amzgachfktch 6L Outdoor Propane | Camping, RVs, and cabins | 11.8 × 5.3 × 17.3 inches; 1.58 GPM |
| ThermoMate CZ422NG | Indoor natural-gas use | Up to 5 GPM; 102,000 BTU |
| Rheem RTG 7.0 GPM | Space-saving whole-home installation | Indoor, wall-mounted design |
| EXCEL Vent-Free | Low-pressure propane setups | Starts at 2 PSI; 1.6 GPM |
| VEVOR 100,000 BTU | Indoor use with visible controls | LED display and ±1°F control claim |
Amzgachfktch 6L Outdoor Propane Water Heater
Best for: Buyers who need a compact, portable heater for outdoor hot water at a cabin, campsite, barn, boat, or RV. Its stated dimensions are 11.8 inches long, 5.3 inches wide, and 17.3 inches high, and it weighs 12 pounds. A foldable handle supports carrying and storage.
The unit is rated at 40,000 BTU per hour and 1.58 gallons per minute. It is designed to heat water on demand and starts at a stated minimum water pressure of 2.5 PSI. The package includes a shower head, gas regulator, garden hose adapter, and installation hardware.
Choose this model if portability and a narrow profile matter more than supplying several household fixtures at once. Its 1.58 GPM output is a limitation for higher-demand whole-house use. The maker also warns that pressure below 2.5 PSI may prevent startup or cause fluctuating temperatures. This is an outdoor unit; confirm the intended installation and local requirements before use.
ThermoMate CZ422NG Indoor Natural Gas Heater
Best for: Households seeking an indoor natural-gas tankless heater with more capacity than a portable camping model. The listed maximum output is 5 GPM, with a 102,000 BTU rating. The manufacturer says it can supply two showers simultaneously under its stated conditions: a 65°F inlet temperature and 105°F output.
The product information describes a flow sensor and control chip that adjust heating frequently, with a claimed temperature consistency of ±1°F. It also lists an oxygen-free copper heat exchanger and multiple protections, including freeze, flame-out, overheat, and timeout safeguards. The listed freeze protection activates at 41°F.
Choose this model if your home uses natural gas and you want an indoor unit with stated multi-point capacity. It is not the right choice if you need a propane heater or an explicitly portable unit. Check the product’s installation, venting, gas-supply, and clearance requirements before purchase; those details should determine whether it fits your space.
Rheem RTG 7.0 GPM Indoor Natural Gas Heater
Best for: Households that want a wall-mounted whole-home heater while freeing floor space. This indoor, non-condensing natural-gas model is rated at 160,000 BTU per hour and up to 7.0 GPM at a 35°F temperature rise. The product information describes capacity for two to three simultaneous showers.
The wall-mount design makes it relevant to buyers comparing slim gas water heaters, though the supplied product details do not state the unit’s exact dimensions. It uses a direct-vent system and has a listed Uniform Energy Factor of 0.82. The manufacturer compares its energy use with a 50-gallon electric tank heater.
Choose this model if whole-home flow and indoor placement are more important than portability. It is not a low-output camping heater, and the stated flow rate depends on temperature rise and incoming water conditions. Confirm the available wall space, venting plan, and installation requirements with a qualified professional before selecting it.
EXCEL Vent-Free Propane Water Heater
Best for: Buyers considering a propane heater for a setup with low incoming water pressure. EXCEL states that this LPG unit starts at 2 PSI and produces up to 1.6 GPM. Its listing describes vent-free technology and says it does not require an expensive flue.
The low startup-pressure figure may be useful for some low-pressure applications, but it should not be treated as a substitute for checking the full installation instructions. At 1.6 GPM, this model is better suited to modest hot-water demand than multiple simultaneous household fixtures.
Choose it if propane fuel and the stated low-pressure startup are central requirements. Avoid choosing it solely because it is described as vent-free: confirm that the appliance is permitted for your intended location and that its installation instructions meet applicable local codes. The supplied product details do not give dimensions, so verify measurements if cabinet or wall clearance is the main concern.
VEVOR 100,000 BTU Indoor Gas Heater
Best for: Buyers who want an indoor gas tankless heater with an LED screen and touch controls. The listed heating capacity is 100,000 BTU per hour. VEVOR describes a smart temperature-control system that aims to keep water within ±1°F of the selected temperature.
The display is intended to show real-time information such as water temperature and operating status. The listing also describes the product as a 4.3-gallon instant water heater, but does not provide a GPM figure in the supplied details. That makes it harder to compare directly with models whose flow rates are specified.
Choose this model if visible operating information and indoor use are priorities. Do not assume it will meet a particular number of simultaneous showers without a confirmed flow rate and temperature-rise specification. Its product information does not state dimensions or fuel type in the supplied features, so verify both before purchase—especially if a narrow installation space or a specific gas supply is required.
Buying Guide: How to Choose a Slim Gas Water Heater
Where will the heater be installed?
Start by separating portable outdoor models from residential indoor units. The Amzgachfktch 6L is explicitly designed for outdoor use and lists its dimensions, weight, handle, and included accessories. The ThermoMate and Rheem models are described as indoor residential heaters. Installation location affects the required venting, clearances, protection from weather, and professional setup.
Do not assume that “slim” means every model has a narrow body. Compare the stated width, height, and depth with the actual space available, including room for connections and required service access. Of the products here, the Amzgachfktch provides exact dimensions. The Rheem describes a wall-mount design but does not include exact dimensions in the supplied details.
Which gas type does your home or setup use?
Match the heater to the available fuel. The ThermoMate and Rheem products listed here use natural gas, while the Amzgachfktch and EXCEL models are propane/LPG products. Do not assume a natural-gas unit can run on propane, or the reverse, unless the manufacturer specifically confirms the configuration. The supplied VEVOR features do not identify its fuel type, so confirm it before buying.
How much hot water do you need at once?
Use the GPM rating as a starting point, not a guarantee of performance under every condition. A portable unit rated at 1.58 GPM serves a different purpose from residential models rated at 5 or 7 GPM. Higher simultaneous demand generally calls for more capacity, but achievable hot-water flow also depends on incoming water temperature and the required temperature rise.
For the ThermoMate, the manufacturer’s two-shower statement is tied to a 65°F inlet temperature and 105°F output. The Rheem’s 7.0 GPM figure is specified at a 35°F temperature rise. Compare products using the same conditions where possible. Do not rely on a shower count alone to size a heater for a household.
Will the heater start with your water pressure?
Check the minimum startup pressure against the water supply at the installation point. The Amzgachfktch lists 2.5 PSI, and EXCEL lists 2 PSI. The Amzgachfktch manufacturer warns that pressure below its threshold can prevent startup or produce inconsistent temperatures. If pressure is low or variable, verify the setup requirements and whether a booster pump is appropriate.
What should you compare beyond the footprint?
- Venting and location: Verify whether the model is indoor or outdoor and what venting method it requires.
- Connections and installation: Check gas supply, water connections, electrical needs, clearances, and whether accessories are included.
- Controls: A display or touch panel may make operating status easier to view, but does not establish capacity.
- Protection features: Compare the specific safeguards listed, such as freeze, overheat, or flame-out protection.
- Documentation: Review the manufacturer’s installation instructions and applicable local requirements before purchase.
Frequently Asked Questions
What is the slimmest gas water heater in this comparison?
The Amzgachfktch 6L is the only product here with exact dimensions in the supplied details: 11.8 × 5.3 × 17.3 inches. Its 5.3-inch width makes it the clearest documented option for buyers prioritizing a narrow portable heater.
Can a portable propane water heater serve a whole house?
The Amzgachfktch portable model is rated at 1.58 GPM and is described for outdoor and mobile uses. That output is different from the higher stated flow rates of residential whole-home models. Match capacity to the number of fixtures and the required temperature rise.
Is a tankless gas water heater suitable for indoor installation?
Some models in this comparison are described as indoor units, including the ThermoMate and Rheem. Installation depends on the model’s venting, clearance, gas, and code requirements. Use the manufacturer’s instructions and qualified installation guidance.
Does a higher GPM rating always mean better performance?
No. GPM must be considered alongside temperature rise, incoming water temperature, and simultaneous demand. A listed flow rate at one temperature rise may not apply at another.
What should I check before buying a low-pressure-start heater?
Compare the heater’s minimum startup pressure with the water pressure at the intended location. Also check installation instructions, expected flow, and the manufacturer’s guidance for fluctuating pressure.