Do you want to find the best condensing tankless water heater?
Condensing tankless water heaters have exhaust gases that can get as low as 100F, which allows cheaper (and easier to install) PVC piping for their vents.
In this product review, I will go over...
- My #1 top pick for the best condensing tankless water heater
- How secondary heat exchangers increase their efficiencies
- Picking the flow rate
Let's get started with this guide!
1. Rinnai RUC98iN
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2. Rinnai RUC98iN
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3. Noritz NRC66DVNG
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4. Rheem RTGH-84DVLN
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5. Rinnai RU98EN
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My Overall #1 Rated Pick
Updated On January 7, 2023
My overall top pick for the best condensing tankless water heater goes to the Rinnai RUC98iN. This indoor ultra efficient heater is rated at 199,000 BTUs and has an energy factor of 0.96. It has a unique feature in that you can choose between concentric or twin vent piping. It has a max flow rate of 9.8-GPM. The water valve kit is included with the RUC98iN.
What Is A Condensing Tankless Water Heater?
Condensing tankless water heaters are much more efficient than standard tankless water heaters.
These highly efficient water heaters can have an efficiency of 93% and higher.
This means that the majority of the heat from the fuel (gas or propane) is transferred to the heated water.
Secondary Heat Exchanger Pre-Heats The Water
Unlike traditional tankless water heaters, condensing units have a secondary heat exchanger. A heat exchanger is a serpentine coil where the water gets heated as gas flows around the water coil.
With condensing tankless heaters, that secondary heat exchanger actually 'pre-heats' the incoming cold water.
The secondary heat exchanger doesn't use gas fuel directly, but it uses the exhaust gases from the primary heat exchanger to pre-heat the water. So when the pre-heated water goes to the primary heat exchanger, it needs less work to heat up the water to the target temperature.
And since these tankless heaters are so efficient, they can literally have the same flow rate as standard tankless units, but with a much lower BTU.
Lower Exhaust Gases
Another nice benefit of condensing tankless heaters is that their exhaust gases are so much lower than standard tankless heaters.
Standard tankless units can have exhaust temperatures in the range of 300F. Since the exhaust gases are so hot, the vent piping needs to be stainless steel double-walled type which can get expensive.
But condensing tankless heaters can have exhaust gases as low as 100F. And because the temperature of the exhaust is so low, schedule 40 PVC plastic piping can be used instead of the double-walled stainless steel.
Picking The Flow Rate For Condensing Tankless Water Heaters
Picking the correct capacity or flow rate of a condensing tankless water heater is crucial. Flow rate is how much water the tankless water heater can deliver based on a GPM or gallon per minute basis.
Most condensing tankless water heaters will have a maximum flow rate in the 5 to 10 GPM range.
To calculate the correct flow rate, you will need to determine how much water your household uses during peak demand. You will also need to calculate the 'temperature rise' or how far the tankless heater will need to raise the cold incoming water. If you live in an area with cold winters, the temperature rise will be much more significant than areas with mild winters.
This means that the flow rate will be reduced as the incoming water gets colder because more energy is required to raise the temperature.
If you undersize the condensing tankless water heater, your hot water supply will be limited. For most homeowners, I would recommend having a qualified plumber determine the correct flow rate for your household.
What Is The Best Condensing Tankless Water Heater?
Here are my full reviews of the top condensing tankless water heater with ultra high efficiencies. Check them out below...
The Rinnai RUC98iN is a highly efficient condensing tankless water heater that has an energy factor rating of 0.96.
This ultra efficient indoor gas heater is rated at 199,000 BTUs and it comes with everything needed for install such as isolation valves and the pressure relief valve. It does not come with the venting pipes however.
This Rinnai heater allows either concentric or twin pipe PVC venting which gives you installation flexibility. The Rinnai RUC98iN is quiet, runs great, and it produces a maximum 9.8 gallons per minute (flow rate).
The Takagi TH3DVN is an ultra efficient condensing tankless water heater that uses natural gas as its fuel. The nice thing about this Takagi heater is that it has computerized safety features so there is no need for a visible pilot light.
It is rated at a very high 199,000 BTUs and it has a maximum 10 gallon flow rate per minute. The Takagi tankless water heater is suitable for up to 4 bathrooms (only 3 in cold climates).
It is manufactured in Japan, and uses a higher quality copper allow for the heat exchanger which is much more efficient than stainless steel.
The Noritz NRC66DVNG is a condensing tankless water heater that is rated at 110,000 BTUs. This tankless unit has an advanced heat exchanger design with a very high efficiency and low NOx emissions.
It includes a built-in temperature controller, a remote thermostat, and a 6-foot power cord. This Noritz heater can produce a max of 6.5 gallons per minute flow rate to satisfy small to medium households.
Since the exhaust gases have such a low temperature, PVC venting pipe can be used on this tankless water heater.
The valve kit which is needed for installation is sold separately.
The Rheem RTGH-84DVLN is a premium tankless water heater that is condensing. This ultra high efficient heater meets low NOx requirements and has an energy factor rating of 0.94.
It is rated at 157,000 BTUs, uses natural gas as its fuel, and has a max flow rate of 8.4-GPM.
A remote control is included with this Rheem tankless heater and it can operate in temperatures as low as -30F.
It also includes a built-in electric blower to help get a very high efficiency.
The Rinnai RU98EN is a high quality condensing tankless water heater that is designed to be installed outdoors. This heater is rated at 199,000 BTUs and it has an energy factor of 0.93 which means it is ultra efficient.
The RU98EN by Rinnai is great for medium to large sized homes, and it has a flow rate of 9.8-GPM. It also is environmentally friendly and meets or exceeds CA and TX low nitrogen oxides emission standards.
This condensing tankless water heater includes the water valves kit needed for installation.
Any time a tankless water heater is installed outside, I recommend ensuring that all water pipes are covered in insulation.
My #1 Top Pick: Rinnai RUC98iN
My top rated pick for the best condensing tankless water heater goes to the Rinnai RUC98iN. Here's why...
Since this tankless heater reuses its exhaust with a secondary heat exchanger, this ultra efficient Rinnai heater can get an energy efficiency of of 96% (energy factor) and produce a max flow rate of 9.8 gallons per minute of water.
#2. Vent Options
This Rinnai condensing tankless water heater has a unique feature in that you have the option of choosing between concentric or twin pipe venting which offers much more installation flexibility than other units.