For outdoor, on-demand domestic hot water, the RTG 7.0 GPM propane and natural gas models offer the highest listed flow rate in this selection. The 5.2 GPM propane unit is a better fit for buyers prioritizing low-flow startup and weather-protection features, while the VELPAX natural gas model adds an indoor remote control. The Rinnai I-Series Plus is a combi boiler for space heating and hot water, but it is not described as an outdoor unit. These products are tankless heaters or a combi boiler, not complete boiler domestic-hot-water kits.
| Product | Fuel | Listed Output | Best For |
|---|---|---|---|
| RTG 7.0 GPM Outdoor Tankless | Propane | 160,000 BTU/hr; 7.0 GPM at 35°F rise | Higher hot-water demand |
| 5.2 GPM Outdoor Tankless | Propane | 130,000 BTU; up to 5.2 GPM | Lower-flow startup and outdoor protection |
| RTG 7.0 GPM Outdoor Tankless | Natural gas | 160,000 BTU/hr; 7.0 GPM at 35°F rise | Higher demand with natural gas |
| Rinnai I-Series Plus Combi Boiler | Natural gas or propane | 150,000 BTU; 96% AFUE stated | Combined space heating and hot water |
| VELPAX Outdoor Tankless | Natural gas | 110,000 BTU; 4.76 GPM | Remote indoor temperature adjustment |
RTG 7.0 GPM Outdoor Propane Tankless Heater
This outdoor propane model is best for households that need a relatively high stated flow rate and have propane service. It is rated at 160,000 BTU per hour and 7.0 GPM at a 35°F temperature rise. The product listing says it can support two to three simultaneous showers, making it a candidate for multi-bathroom homes with overlapping hot-water use.
Its non-condensing design has a listed 0.82 Uniform Energy Factor. The listing also says outdoor installation eliminates the need for venting and describes a metal cabinet intended for wall mounting by a qualified installer. Choose this model over smaller-output options if the listed flow and propane fuel match the home’s requirements.
Limitation: The 7.0 GPM rating is specified at a 35°F rise. Actual delivered flow depends on incoming water temperature and required outlet temperature, so that number should not be treated as a guaranteed flow rate in every climate.
5.2 GPM Outdoor Propane Tankless Heater
This 130,000 BTU propane heater is best for buyers who want an outdoor tankless unit with a stated minimum flow requirement of 0.79 GPM and minimum water pressure of 0.025 MPa. The listing says it can supply up to 5.2 GPM and serve three to four outlets simultaneously. That outlet count is a manufacturer claim; compare it with the home’s expected demand and local incoming-water conditions.
Features include a corrosion-resistant body, stainless steel vent, variable-frequency fan, wind-resistant design, and stated windproof, freeze-proof, and IPX6 waterproof protection. Its thermostat system is described as maintaining temperature within ±1°F, and the listing identifies seven-segment, four-stage layered combustion.
Limitation: Its maximum listed flow is below the 7.0 GPM RTG models. Buyers should also verify the installation instructions and freeze-protection requirements for their location rather than assuming that a “freeze-proof” description eliminates all cold-weather precautions.
RTG 7.0 GPM Outdoor Natural Gas Heater
This natural gas version is best for households with natural gas service that need the same listed output as the propane RTG model. It provides 160,000 BTU per hour and is rated at 7.0 GPM at a 35°F temperature rise. The product information says it is designed for whole-house use and may serve two to three simultaneous showers.
The unit is a non-condensing outdoor tankless heater with a stated 0.82 UEF. Its outdoor installation is described as eliminating venting, and its durable metal cabinet supports wall mounting by a qualified installer. Choose this model instead of the propane version only if the home’s gas supply and approved installation setup match the natural gas model.
Limitation: This is a natural gas appliance, not a dual-fuel model according to the supplied product details. Confirm fuel type, gas supply capacity, required clearances, and local installation rules before selection.
Rinnai I-Series Plus Combi Boiler
This 150,000 BTU combi boiler is best for buyers who need one appliance to provide both home heating and domestic hot water. The product details identify natural gas or propane operation, a stated 96% AFUE rating, and Smart Sense Gas Valve technology for energy management. Unlike the other products here, it is presented as a heating-and-hot-water appliance rather than a dedicated outdoor tankless water heater.
Choose this option when the project involves replacing or designing a combined space-heating and hot-water system. Its role makes it more relevant to a “boiler domestic hot water” search than a standalone water heater, but the product information does not establish that it is intended for outdoor installation or that it includes all components needed for a complete system.
Limitation: Do not assume this is an outdoor boiler kit. Confirm whether the installation location, system design, and required accessories are supported by the manufacturer and a qualified heating professional.
VELPAX 4.76 GPM Outdoor Natural Gas Heater
This VELPAX model is best for natural gas users who value an indoor control panel for an outdoor-mounted heater. It is listed at 110,000 BTU and 4.76 GPM, with a stated operating water-pressure range of 3–116 PSI. The 16.4-foot cable connects the outdoor unit to a digital remote panel, which displays and adjusts the hot-water setting indoors.
The listing says the heater can serve three to four outlets and has a maximum outlet temperature of 149°F. It also describes auto ignition, staged combustion, and an oxygen-free copper heat exchanger. The compact listed dimensions are 15 by 7.4 by 24 inches.
Limitation: The product requires a 110V, 60Hz AC power supply and has a lower listed flow rate than the 7.0 GPM options. Check electrical access and expected simultaneous demand before choosing it.
Buying Guide: How to Choose an Outdoor Domestic Hot Water Heater
Do you need a boiler or a tankless water heater?
The phrase “outdoor boiler domestic hot water kit” can refer to more than one system type. A tankless water heater heats domestic water on demand. A combi boiler can provide domestic hot water while also serving a space-heating system. A complete kit may require additional parts, controls, piping, or installation materials, but the product details supplied here do not confirm that any of these listings includes a complete kit.
Start by identifying whether the project is only for taps, showers, and appliances, or whether it must also heat the home. For domestic hot water alone, compare the outdoor tankless units. For combined space heating and hot water, evaluate the combi boiler with a heating professional.
Which fuel does the home use?
Match the appliance to the available fuel. The RTG 7.0 GPM models are sold in separate propane and natural gas versions. The 5.2 GPM unit is listed as propane, while the VELPAX model is listed as natural gas. The Rinnai combi boiler details state natural gas or propane functionality, but buyers should confirm the exact model configuration.
Do not choose based only on a general fuel description. Confirm the appliance’s specific fuel designation, gas-line capacity, and installation requirements. A qualified installer can assess whether the existing supply is appropriate for the selected unit’s BTU input.
How much hot-water flow do you need?
Estimate which fixtures may run at the same time, such as showers, kitchen taps, and laundry. Compare that combined demand with the product’s rated flow under the stated temperature-rise conditions. The RTG models list 7.0 GPM at a 35°F rise; the 5.2 GPM unit lists up to 5.2 GPM, and the VELPAX lists 4.76 GPM.
Flow ratings are not interchangeable without considering temperature rise. Colder incoming water requires a larger temperature increase to reach a chosen outlet temperature, which can affect available flow. Ask an installer to size the heater for the local climate, household demand, and desired hot-water temperature.
Will the unit be installed outdoors?
Outdoor units must be installed according to their instructions and applicable local requirements. Compare cabinet construction, stated weather protections, clearances, access for service, and exposure to wind or freezing temperatures. The 5.2 GPM product specifically lists wind-resistant, freeze-proof, and IPX6 waterproof protection; verify what those claims mean for the installation conditions.
Outdoor placement does not mean maintenance or protection can be ignored. Confirm how the heater should be protected during cold weather, what clearances are required, and whether the location permits safe access for inspection and servicing.
What controls and power connections are required?
The VELPAX includes a described indoor digital remote control connected by a 16.4-foot cable and requires 110V, 60Hz AC power. The other listed features do not provide equivalent control or electrical details. Review the full product documentation for power, ignition, control, and wiring requirements before purchase.
What should be confirmed before buying?
- Whether the project needs domestic hot water only or both hot water and space heating.
- The exact fuel type and whether the existing supply can support the appliance.
- Expected simultaneous fixture use and the heater’s output at the local temperature rise.
- Outdoor clearances, weather exposure, freeze protection, and service access.
- Whether required accessories, controls, piping, and installation materials are included.
- Local code and permit requirements, checked with a qualified installer or authority.
Frequently Asked Questions
Is an outdoor tankless water heater the same as an outdoor boiler?
No. A tankless water heater supplies domestic hot water on demand. A boiler is generally part of a space-heating system and may also provide domestic hot water in a combi configuration. Check the intended application before selecting equipment.
Which listed product has the highest stated flow rate?
The RTG natural gas and propane models each list 7.0 GPM at a 35°F temperature rise. That rating depends on the stated rise and should not be assumed for every incoming-water temperature.
Which option includes an indoor remote control?
The VELPAX outdoor natural gas heater is listed with an indoor digital remote control and a 16.4-foot connection cable. Its product details also specify a 110V, 60Hz AC power supply.
Can the Rinnai combi boiler be installed outdoors?
The supplied product information does not say that the Rinnai I-Series Plus is designed for outdoor installation. Confirm the approved location and installation requirements in the manufacturer’s documentation before considering it for an outdoor setup.
Are these products complete domestic hot-water kits?
The supplied listings describe heaters or a combi boiler, but do not establish that any includes every component needed for a complete installation. Check the product documentation and consult an installer about required accessories and system parts.