For whole-home hot water, the Rheem RTG models and MIZUDO indoor tankless unit are the relevant options in this product list; each is a natural gas water heater, and the Rheem listings specify an indoor direct vent system. The Comfort Glow products are direct vent wall heaters for room heating, not water heaters, so they are not substitutes. Compare stated flow rates and household demand, and confirm venting and installation requirements before choosing.
| Product | Product type | Best suited for |
|---|---|---|
| Rheem RTG 7.0 GPM | Tankless water heater | Homes with moderate simultaneous demand |
| Rheem RTG 8.4 GPM | Tankless water heater | Homes with higher simultaneous demand |
| MIZUDO 199,000 BTU | Tankless water heater | Buyers prioritizing listed flow and temperature controls |
| Comfort Glow 17,000 BTU | Room heater | Heating a room, not domestic water |
| Comfort Glow 8,000 BTU | Room heater | Heating a smaller room, not domestic water |
Rheem RTG 7.0 GPM Tankless Water Heater
This indoor, non-condensing natural gas model is listed at 160,000 BTU per hour and up to 7.0 gallons per minute at a 35°F temperature rise. Rheem describes it as suitable for two to three simultaneous showers or water points, with a wall-mount design intended to save floor space. Its listed UEF is 0.82.
Best for: Households seeking a whole-home tankless unit with moderate concurrent hot-water demand. It was selected because the product listing specifically identifies indoor installation with a direct vent system. Limitation: Its stated flow rate is lower than the other listed Rheem model, and actual capacity depends on the temperature rise and demand.
Rheem RTG 8.4 GPM Tankless Water Heater
This indoor, non-condensing model provides 180,000 BTU per hour and is listed at up to 8.4 GPM at a 35°F temperature rise. The manufacturer describes it as suitable for three to four simultaneous showers or water points. It also has a wall-mount design and a listed UEF of 0.82. The product information specifies an indoor direct vent system.
Best for: Larger households or homes with several bathrooms that need more simultaneous hot-water capacity than the 7.0 GPM model lists. Choose this if the higher stated flow rate better matches your expected demand. Limitation: The 8.4 GPM figure is tied to a 35°F temperature rise; it should not be assumed at every incoming-water temperature.
MIZUDO 199,000 BTU Indoor Tankless Heater
MIZUDO lists up to 10.3 GPM and 199,000 BTU of heating input, with capacity described for concurrent use across two to three bathrooms and other fixtures. Its product details state temperature control within ±1°F, a default setting of 107°F, an adjustable range up to 149°F, and a 0.53 GPM low-flow activation threshold.
Best for: Buyers comparing high listed flow, low-flow activation, and adjustable temperature controls. It was selected as an indoor natural gas tankless water heater for whole-home demand. Limitation: The provided product details do not specify a direct vent system, so confirm venting configuration and installation requirements with the manufacturer or a qualified installer before treating it as a match for a direct-vent setup.
Comfort Glow 17,000 BTU Direct Vent Wall Heater
This is a room-heating appliance, not a water heater. The listing says it produces 17,000 BTU and heats up to 500 square feet. Features include thermostatic heat control, a sealed burn system, electronic ignition, a safety pilot, and a built-in pressure regulator. Its stated dimensions are 20 inches high, 27.3 inches wide, and 6.5 inches deep.
Best for: Someone shopping for direct vent natural gas heat in a room of up to the listed area, rather than for household hot water. It is included to distinguish a similarly described direct vent product from a water heater. Limitation: It does not heat water for showers, sinks, or appliances.
Comfort Glow 8,000 BTU Direct Vent Wall Heater
The Comfort Glow DVN08 is a natural gas wall heater rated at 8,000 BTU, with a stated heating area of up to 250 square feet. Its listed features include a sealed burn system, matchless piezo ignition, a safety pilot, and a built-in pressure regulator. The product dimensions are 29.5 inches high, 16.75 inches wide, and 9.8 inches deep.
Best for: Buyers seeking supplemental room heat for a smaller area. It is not a water-heating option, but its inclusion helps prevent confusion between direct vent wall heaters and direct vent water heaters. Limitation: It cannot supply domestic hot water.
Buying Guide: How to Choose a Direct Vent Natural Gas Water Heater
Is it actually a water heater?
Check whether the product heats water for plumbing fixtures or heats the air in a room. Tankless water heaters are rated by water flow and heating input; wall heaters are commonly described by room coverage and BTU output. A direct vent wall heater is not a replacement for a water heater.
How much hot water does the household use at once?
Estimate which fixtures may run simultaneously, such as showers, sinks, and a dishwasher. Compare that demand with the product’s stated flow rate and the temperature-rise condition attached to it. The Rheem 8.4 GPM model lists a higher flow rate than the 7.0 GPM model at the same stated temperature rise.
What should buyers verify about venting?
Do not assume all indoor gas tankless models use the same vent arrangement. The Rheem listings specify an indoor direct vent system, while the supplied MIZUDO details do not state its venting configuration. Confirm the exact requirements, fuel supply, and installation conditions before purchase.
Should you compare temperature controls and activation flow?
These details can matter for specific household routines. MIZUDO lists a 0.53 GPM activation threshold and temperature adjustment up to 149°F. Review the manufacturer’s instructions and household needs rather than assuming a listed setting is appropriate for every use.
Frequently Asked Questions
What is a natural gas direct vent water heater?
It is a water-heating appliance that uses natural gas and a specified venting system to handle combustion air and exhaust. Verify the product’s installation documentation to confirm the exact configuration.
Are the Comfort Glow products water heaters?
No. Both Comfort Glow products listed here are direct vent wall heaters for room heating, not appliances that heat domestic water.
Which listed water heater has the highest stated flow?
The MIZUDO listing states up to 10.3 GPM. Its provided details do not specify a direct vent system, so verify venting before selecting it for that requirement.
Is a higher GPM always better?
No. Choose capacity based on simultaneous household demand and the expected temperature rise. A higher maximum flow may be unnecessary for a smaller household.
Do the Rheem models specify direct vent installation?
Yes. Both Rheem listings describe indoor installation with a direct vent system. Confirm the installation details for the home before purchase.