Few things are more frustrating than the sudden shock of a cold shower because someone else ran the dishwasher or took a bath. If your current water heater can't keep up, you might think the only fix is shelling out for a massive new tank — but there's a smarter option.
At PlumbersCrib.com, we recommend the Rheem RTEX-AB7 Water Heater Booster — a compact device that delivers up to 45% more hot water from your existing tank, without the big-tank price tag or the footprint to match.* No new tank, no major plumbing overhaul. Just more hot water from what you already have.
*According to independent testing at 1.5 GPM shower flow rate.
How the Rheem Water Heater Booster Works
The RTEX-AB7 installs directly on the hot water outlet of your existing tank. It continuously monitors the outlet temperature and kicks on automatically when the water drops below your set activation point — effectively extending your tank's capacity without changing the tank itself.
Independent testing shows that a shower can run for nearly twice as long with the booster in place compared to the tank alone. At roughly the size of a shoebox (12-5/8" W × 8-1/4" H × 3-5/8" D), it mounts directly to your tank or on a nearby wall — making it a practical option even in tight utility closets where a larger tank simply won't fit. It works with both gas and electric tank-type water heaters.
Sizing Impact: What Tank + Booster Gets You
One of the most practical aspects of the Water Heater Booster is how dramatically it upgrades your effective tank size. Here's what to expect:
- 19-gallon short + Booster = 30-gallon short performance
- 30-gallon short + Booster = 40-gallon medium performance
- 19-gallon medium + Booster = 50-gallon tall performance
- 50-gallon tall + Booster = 80-gallon performance
- 80-gallon + Booster = 120-gallon performance
Key Features
- Vacation Mode: Works with electric tanks to cut power to the tank while you're away, saving on standby energy costs
- Eco Mode: Works with electric tanks to conserve energy by cycling the tank on and off on a set schedule
- Adjustable Activation Temperature: Set the inlet temperature (80–130°F) at which the booster activates
- Adjustable Max Temperature: Set the maximum outlet temperature the booster will heat to (80–140°F), adjustable in 1°F increments
- Freeze Protect: Works with electric tanks to automatically power the tank on if the inlet thermistor reads below 60°F
- Digital Interface: Easy-to-read display with simple controls
- Field-Replaceable Heating Element: Serviceable in the field without replacing the entire unit
Installation: Electric and Gas Tanks
The RTEX-AB7 is designed for a one-trade install that typically takes 45 minutes or less. When installed on an existing electric tank, it uses the tank's existing electrical infrastructure — no new breaker or wiring run required in most cases. For gas tanks, a dedicated 30-amp double-pole breaker is required. The unit can be mounted directly on the tank's hot water outlet or wall-mounted nearby if space is limited.
Before starting, confirm you have the required clearances: 14" of straight pipe clearance above the tank is needed for installation, and 6" of clearance to the front and sides must be maintained for ongoing service access. Do not use Teflon tape or pipe dope on the fittings. Once both water lines are connected, Rheem requires running water through the unit for 2–3 minutes to purge any air pockets before turning on any electrical power — skipping this step can cause permanent damage to the unit. Installation must be performed by a licensed electrician and plumber.
Water connections are 3/4" FNPT inlet and 3/4" MNPT outlet, with 1/2" copper tube fitting adapters included. The unit mounts horizontally with the inlet on the bottom and outlet on the top.
Specifications
- Model Number: RTEX-AB7
- Power: 7.2 kW
- Voltage: 240V, single phase
- Max Amps: 30A
- Breaker Required: 1 × 30-amp double-pole
- Dimensions: 12-5/8" W × 8-1/4" H × 3-5/8" D
- Weight: 5.64 lbs.
- Pre-Set Outlet Temp: 120°F
- Pre-Set Activation Temp: 115°F
- Water Connections: 3/4" FNPT inlet / 3/4" MNPT outlet
- Certifications: ETL listed to UL 499/CSA; Low lead certified to ANSI/NSF 372 by WQA
- Warranty: 5-year heating chamber, 1-year parts
Frequently Asked Questions
Does the Rheem Water Heater Booster work with a gas tank?
Yes. The RTEX-AB7 is compatible with both gas and electric tank water heaters. The main difference is electrical: on an existing electric tank, the booster can typically use the tank's existing wiring infrastructure. On a gas tank, a dedicated 30-amp double-pole breaker is required since the gas tank doesn't already have that circuit in place.
How long does installation take?
Rheem rates the RTEX-AB7 as a one-trade install that takes as little as 45 minutes — significantly faster than removing and replacing a full tank. The unit connects to the hot water outlet of your existing tank and can be mounted directly on the tank or on a nearby wall if space is tight.
How much more hot water does the booster actually deliver?
According to independent testing at a 1.5 GPM shower flow rate, the booster increases deliverable hot water by up to 45%. In practical terms, that's roughly the equivalent of jumping up one full tank size — a 50-gallon tank performs like an 80-gallon, and an 80-gallon performs like a 120-gallon.
At what temperature does the booster activate?
The unit comes pre-set from the factory at a 115°F activation temperature and 120°F max outlet temperature. Both are fully adjustable — activation temperature can be set anywhere from 80–130°F, and max outlet temperature from 80–140°F, in 1°F increments. The booster monitors the tank's hot water outlet and switches on automatically when the water drops below your set activation point.
What happens if I go on vacation?
The RTEX-AB7 includes a Vacation Mode that works with electric tanks to shut off power to the tank while you're away — so you're not paying to maintain hot water no one is using. It also has an Eco Mode for electric tanks that cycles the tank on and off on a set schedule for day-to-day energy savings.
Is there freeze protection?
Yes, for electric tanks. The Freeze Protect feature automatically powers the tank back on if the booster's inlet thermistor senses that the tank outlet temperature has dropped below 60°F, helping prevent freeze damage in cold climates or unconditioned spaces.
Are there any clearance requirements for installation?
Yes. The install guide specifies 14" of straight pipe clearance above the existing tank for the unit to fit properly, and 6" of clearance to the front and sides for service access. Additionally, do not use Teflon tape or pipe dope on the fittings. After connecting both water lines, you must run water through the unit for 2–3 minutes to flush out any air pockets before energizing — Rheem states that skipping this purge step can cause permanent damage to the unit.
What is the warranty on the RTEX-AB7?
The Rheem RTEX-AB7 carries a 5-year limited warranty on the heating chamber and a 1-year limited warranty on parts. See the Residential Warranty Certificate for complete terms.
Why Order from PlumbersCrib.com?
- Free Shipping: All water heaters ship free within the contiguous United States on orders over $199
- Wholesale Pricing: We offer competitive pricing direct to homeowners and contractors
- Trusted Support: Our team is available to help you choose the right product and answer technical questions — call us at 877-881-5501
Ready to stop running out of hot water? Browse the Rheem RTEX-AB7 Water Heater Booster at PlumbersCrib.com today.