Our Top Picks
- Up to 11.1 GPM, 199,000 BTU
- 0.98 UEF condensing
- Gas or propane, indoor or outdoor
- Can be installed horizontally or vertically
- Fully automatic
- Works with low water pressure (8 psi)
- 3.5-inch LED touchscreen
- Compact, 26 lbs
- 0.86 UEF condensing
- Weighs just 39 lbs
- Remote controlled thermostat
- 12-year warranty
Our Review Criteria: Uniform Energy Factor decides a condensing water heater, because efficiency is the reason to pay for condensing technology at all. We compared each unit’s UEF against ENERGY STAR and Department of Energy efficiency ratings, then weighed GPM flow, BTU input, venting type, and warranty length. We checked every manufacturer’s published figures against verified owner feedback before settling the rankings. We confirm each pick is currently sold and in stock and swap out any model that goes out of production.
A standard gas water heater sends a lot of its heat straight up the flue. A condensing unit captures that exhaust heat and uses it to preheat incoming water, so less of what you pay for disappears out the vent.
That recycled heat is what makes these the efficiency pick for gas households, cutting fuel waste without cutting into your hot water supply.
In this guide we explain how the technology works, walk through what to check before you buy, and share our picks for the best condensing water heaters this year, judged on flow rate, venting requirements, and how well each unit fits a real household.
How Do Condensing Water Heaters Work?
A condensing water heater runs exhaust gas through a second heat exchanger to pre-warm incoming water, so heat that would go up the vent goes into the water instead. Standard tankless water heaters, by contrast, burn gas and send that hot exhaust straight out a vent, wasting the energy in it. Water heating already accounts for up to 20 percent of a typical home’s energy use, so capturing that lost heat translates directly into a lower gas bill (1).
This process squeezes every ounce of energy from the fuel. These units typically reach a Uniform Energy Factor (UEF) of 0.90 or higher, meaning 90 percent or more of the fuel becomes hot water instead of wasted exhaust. ENERGY STAR certifies a gas tankless model only at a UEF of 0.95 or higher, with a maximum flow of at least 2.8 GPM over a 67 degree rise (2).
Things to Consider
Before you invest in a new system, here are the critical factors that should drive your decision.
Tank vs. Tankless
While most condensing technology is found in tankless units, it helps to understand the distinction if you are transitioning from an older system.
Tank
Traditional tank heaters store 40 to 50 gallons of hot water 24/7. They are generally cheaper upfront and simpler to install. However, they suffer from “standby loss” because they constantly burn fuel to keep the water hot, even when you aren’t home.
We did not include any standard tank units in this list because condensing technology has largely shifted toward tankless designs for maximum efficiency.
Pros
- Lower upfront cost.
Cons
- Limited hot water supply.
- Higher energy bills due to standby heat loss.
Tankless
Tankless units heat water on demand. When you open a tap, the burners ignite and heat the water as it flows through the exchanger. This offers an endless supply of hot water, provided you don’t exceed the flow rate capacity.
Because they don’t store hot water, they are significantly more efficient. The initial price tag is higher, but the long-term savings on gas bills often make up for it.
Pros
- Endless hot water supply.
- Compact, wall-mounted design saves floor space.
- Significant energy savings.
Cons
- Higher initial purchase price.
- May require venting upgrades.
Digital vs. Remote Interface
Controlling your water temperature shouldn’t be a hassle. Manufacturers generally offer two ways to interact with the unit.
Integrated Digital Panel
Many units have a control panel built directly onto the front casing. This is straightforward and reliable. However, if your heater is installed in a crawl space, attic, or basement, making adjustments can be inconvenient.
Pros
- Simple and durable.
- No wiring for external controllers required.
Cons
- Inconvenient if the unit is installed in a hard-to-reach area.
Remote Thermostat
Some models come with (or support) remote controllers. These can be mounted in a bathroom, laundry room, or kitchen. This allows you to adjust the output temperature without trekking to the utility room.
Pros
- Adjust temperature from the comfort of your living space.
- Great for prioritizing hotter water for laundry or dishwashers.
Cons
- Requires running wire from the unit to the controller location.
Product Reviews
We evaluated these units based on efficiency ratings, flow rate capacity, build quality, and ease of installation.
Rinnai RX199iN Condensing Tankless Water Heater
Highest Flow Rate
The Rinnai RX199iN is built for households that never want to run out of hot water. It delivers up to 11.1 gallons per minute from a 199,000 BTU burner, enough to run several fixtures at once, so the morning shower-and-laundry rush stops being a fight.
It is a true condensing unit with a 0.98 UEF, which puts it among the most efficient gas water heaters you can buy. A second heat exchanger pulls warmth from the exhaust, so it also vents through inexpensive PVC. The Smart Sense gas control runs on natural gas or propane, and the same unit installs indoors or outdoors with Rinnai’s Versa Vent.
What We Like
11.1 GPM of Real Capacity
Up to 11.1 GPM from a 199,000 BTU burner supplies as many as seven fixtures at once, so a busy family is not rationing hot water at peak hours. In colder regions where incoming water is near freezing, you still get enough flow for two showers plus an appliance.
0.98 UEF Efficiency
The condensing design recovers heat from the exhaust and reaches a 0.98 Uniform Energy Factor, near the ceiling for a gas unit. More of every therm becomes hot water instead of warming the outdoors.
Flexible Fuel and Mounting
Smart Sense adapts to natural gas or propane, and Versa Vent lets the same model install indoors or outdoors. One unit fits more homes without special-ordering a variant, and the cool exhaust vents through cheap PVC.
What We Don't Like
Premium Price and Pro Install
At 199,000 BTU the unit needs a correctly sized gas line and a professional installer, plus a condensate drain with a neutralizer. It is one of the pricier picks here, so budget for setup, not just the heater.
Product Specs
| Dimensions | 25.8 x 18.5 x 11.4 inches |
|---|---|
| Weight | 55 pounds |
| Flow Rate (Gallons Per Minute) | 11.1 GPM |
| Input Type | Gas operated |
| Digital or Remote? | Digital |
| Indoor or Outdoor Use? | Indoor or outdoor |
EZ Ultra HE Condensing Tankless Water Heater
Most Efficient Condensing Water Heater
The EZ Ultra HE is designed for the budget-conscious homeowner who doesn’t want to sacrifice condensing efficiency. It offers a very attractive price point while still delivering the energy savings of a condensing unit.
It is particularly popular for DIY-friendly installations (though we always recommend a pro for gas lines) because of its straightforward connections and flexible venting options.
What We Like
Exhaust Gas utilization
This unit excels at capturing latent heat. By utilizing the exhaust gas so effectively, it ensures that the unit runs cooler and uses less propane or natural gas than non-condensing competitors.
Simple Venting
You can run a single 2-inch PVC pipe for the exhaust. This is cheap, easy to cut, and easy to source at any local hardware store. It simplifies the most intimidating part of the installation process.
Low Pressure Operation
It can ignite with very low water pressure (as low as 8 PSI). If you live in a rural area with a well pump or have older plumbing with inconsistent pressure, this heater is forgiving and reliable.
What We Don't Like
Slow Ignition Time
Users note that it can take a few seconds longer to fire up and deliver hot water compared to the premium Rinnai and Noritz models higher on this list. It’s not a dealbreaker, but it is noticeable if you are used to instant systems.
Product Specs
| Dimensions | 27 x 14.5 x 6.5 inches |
|---|---|
| Weight | 31 pounds |
| Flow Rate (Gallons Per Minute) | 3.4 GPM |
| Input Type | Gas operated |
| Digital or Remote? | Digital |
| Indoor or Outdoor Use? | Indoor |
ThermoMate CZ480NG Condensing Tankless Water Heater
Most Aesthetically Pleasing
The ThermoMate CZ480NG is the most modern-looking unit on this list, fronted by a 3.5-inch LED touchscreen that shows the set temperature, flow rate, and any error codes at a glance. The compact silver cabinet is roughly a third the size of a tank heater, so it stays clean-looking even mounted in plain sight.
It is a genuine condensing unit, pairing a stainless steel condensing exchanger with an oxygen-free copper one for a 0.86 UEF. At 5.28 GPM and 114,000 BTU it suits a smaller home or a one-to-two-bathroom household rather than a high-demand house, and it lands well under the price of the premium brands.
What We Like
Modern Touchscreen Interface
The 3.5-inch LED touchscreen makes setting and monitoring temperature simple, and it looks far better than the basic dials or panels you find on most value-priced units.
Condensing Efficiency on a Budget
A dual heat-exchanger design earns a 0.86 UEF, so you get condensing-level savings at a price much closer to a non-condensing unit. The cool exhaust still vents through inexpensive PVC.
Compact and Light
At about 21.7 by 13.8 by 7 inches and 26 pounds, it is the easiest unit here to wall-mount in a small closet or utility nook, and it bundles freeze, overheat, flame-out, and over-pressure protection.
What We Don't Like
Limited Flow Rate
At 5.28 GPM it cannot keep up with several simultaneous showers, so it suits smaller homes. A larger, high-demand household should size up to one of the higher-GPM units here.
Condensate Drain Needed
Like any condensing heater it produces mildly acidic condensate, so plan for a drain and an inexpensive neutralizer kit to protect your pipes.
Product Specs
| Dimensions | 21.7 x 13.8 x 7 inches |
|---|---|
| Weight | 26 pounds |
| Flow Rate (Gallons Per Minute) | 5.28 GPM |
| Input Type | Gas operated |
| Digital or Remote? | Digital |
| Indoor or Outdoor Use? | Indoor |
Noritz NRC66DVNG Indoor Condensing Tankless Water Heater
Smallest Condensing Water Heater
Noritz creates units that focus on reliability and ease of retrofitting. The NRC66 is specifically designed for smaller homes, apartments, or condos where space is a luxury.
It features dual stainless steel heat exchangers, which are highly resistant to corrosion and scale buildup. If you are looking to replace a 40-gallon tank heater with something that takes up zero floor space, this is a solid contender.
What We Like
Ultra-Compact Design
This unit is incredibly unobtrusive. You can install it in a closet, a small utility room, or even under a staircase. The white finish is clean and modern, so it doesn’t look like an industrial eyesore if it happens to be visible.
Remote Included
Unlike some competitors that make you buy the controller separately, Noritz includes a remote thermostat. You can mount this in your kitchen or bathroom to easily adjust the temperature or view error codes without accessing the unit itself.
Lower Activation Flow
This unit activates at a flow rate of just 0.5 GPM. This means you don’t have to turn the faucet on full blast just to trigger the hot water, which is great for shaving or light washing.
What We Don't Like
Lower Total Capacity
This unit tops out at around 6.6 GPM. While that is plenty for a 1-2 bathroom home, it will struggle in a larger house with high demand. It is strictly a residential solution for smaller families or couples.
Product Specs
| Dimensions | 6.7 x 13.8 x 23.6 inches |
|---|---|
| Weight | 39 pounds |
| Flow Rate (Gallons Per Minute) | 6.6 GPM |
| Input Type | Gas operated |
| Digital or Remote? | Remote |
| Indoor or Outdoor Use? | Indoor |
| Product | Award | Dimensions | Weight | Flow Rate | Input Type | Digital/ Remote | Indoor/ Outdoor |
|---|---|---|---|---|---|---|---|
| Rinnai RX199iN | Highest Flow Rate | 25.8″ x 18.5″ x 11.4″ | 55 lbs | 11.1 GPM | Gas | Digital | Indoor/outdoor |
| EZ Ultra HE | Most Efficient Condensing Water Heater | 27″ x 14.5″ x 6.5″ | 31 lbs | 3.4 GPM | Gas | Digital | Indoor |
| ThermoMate CZ480NG | Most Aesthetically Pleasing | 21.7″ x 13.8″ x 7″ | 26 lbs | 5.28 GPM | Gas | Digital | Indoor |
| Noritz NRC66DVNG | Smallest Condensing Water Heater | 6.7″ x 13.8″ x 23.6″ | 39 lbs | 6.6 GPM | Gas | Remote | Indoor |
