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Navien 240A Vs 240S: Which Tankless Water Heater is Better?

Navien 240A Vs 240S tankless water heater debate is going on. How do these two water heaters stack up against each other? And which one is right for your home?

Well, both models are part of the NPE-2 Series, a big update to the successful NPN tankless water heaters.

Notable improvements include common venting for 12 units (up from 8) and cascading capacity of 32 units (up from 16). Other perks include a minimum load requirement of 6.67%, easy setup, advanced multi-line control, and improved flow rate.

But what is the difference between Navien NPE 240A and NPE 240S? I’ll be reviewing both units so you can decide which product is right for you. Basically, I’ll be comparing their specs, features, benefits, and flaws. Keep reading to find out!

Navien 240A vs 240S

Overview of Navien 240A


  • Efficiency Rating: 0.95
  • Max GPM(67°F Rise): 5.6
  • Minimum Flow Rate Requirement: Less than 0.01 GPM
  • Water Pressure:15–150 PSI
  • Installation Type: Indoor/Outdoor

The Navien 240A indoor/outdoor water heater features an exclusive ComfortFlow recirculation mode. It has an internal pump and buffer tank that offer instant hot water whenever you want it. You can activate the recirculation pump with an optional HotButton add-on accessory so you can have hot water whenever you need it.

Navien 240A residential/commercial water heater provides both domestic hot water and space heating. You can achieve the latter using the optional H2Air Kit. Also, this unit features stainless steel heat exchangers for longer life and faster heating.

Navien NPE 240A tankless water heater is compatible with standard ½-inch gas lines up to 24 feet. Also, it uses simple 2-inch or 3-inch PVC forced draft direct venting up to 60 feet. For this reason, it cuts installation time by half.

This condensing water heater has a BTU rating of 19,900–199,900 per hour. It can use natural gas or propane gas at the supply pressure of 3.5″–10.5″ WC and 8″–13″ WC.


  • Quicker hot water delivery
  • No minimum flow rate requirements
  • Offer space heating
  • Optional handheld remote


  • The pump uses extra energy
  • Requires extra plumbing

Overview of Navien 240S


  • Efficiency Rating: 0.96
  • Max GPM(67°F Rise): 5.8
  • Minimum Flow Rate Requirement: 0.5 GPM
  • Water Pressure:15–150 PSI
  • Installation Type: Indoor/Outdoor

Navien NPE 240 Standard uses ultra condensing technology, making it the most energy-efficient. It has an energy factor of 96-99%, which means it can save you money on your energy bills.

Navien 240S requires a minimum of 19,900 BTUs, peaking out at 199,900 BTU/hour. Also, it uses dual stainless steel heat exchangers for longer life and faster heating.

You can use it for both residential and commercial applications. Plus, it is a field gas convertible.  It can run on natural gas at 3.5″–10.5″ WC or propane gas at 8″–13″ WC. Plus, it hooks up to your existing ½-inch gas pipe.

Venting Requirements are pretty straightforward. Use 2-inch or 3-inch PVC forced draft direct vent with zero clearance to combustibles. Such simplicity and the fact that it doesn’t need additional plumbing lowers installation costs and time significantly.


  • Lightweight
  • Industry’s top-rated energy efficiency
  • Lower installation and operating cost


  • Takes longer to deliver hot water

Comparison table: Navien 240A Vs 240S

 NPE 240ANPE 240S
BTU Rating19,900–199,900  19,900–199,900
Uniform Energy Factor0.950.96
Max GPM(67°F Rise)5.65.8
Min Flow Rate RequirementLess than 0.01 GPM0.5 GPM
Water Pressure15–150 PSI15–150 PSI
Installation TypeIndoor/OutdoorIndoor/Outdoor
Connection Size3/4″ NPT3/4″ NPT
Vent Type2-inch PVC forced draft direct vent2-inch PVC forced draft direct vent
Dimensions (W x H x D)17.3″ x 27.4″ x 13.2″17.3″ x 27.4″ x 13.2″
Weight77 Pounds73 Pounds
Special FeatureBuffer Tank and Recirculation Pump 
Warranty15 Years15 Years

Navien 240A Vs 240S: What are the key differences?

The main difference between NPE 240A and NPE 240S is the recirculation mode. NPE 240A has ComfortFlow recirculation mode, comprising a buffer tank and a recirculation pump – the NPE 240S doesn’t.

This extra feature brings out some key differences between the two Navien water heaters. I’ll break down the key differences based on efficiency rating, wait time, minimum flow rate, plumbing, optional accessories, and cost.

I hope it will help make your purchasing decision a little easier.

navien tankless water heater 240a vs 240s

Energy Efficiency

The first noticeable difference is in the  (UEF) uniform energy factor, the newest rating for water heater efficiency. The higher, the better.

Well, both models are one of the most energy-efficient on the market. However, NPE 240S has a higher rating of 0.96, with NPE 240A registering 0.95.

Why the difference? The 240A  model requires extra energy to run the recirculation pump and Maintain the water temperature in the recirculation loop.

However, according to the Navien 240A manual, the extra energy is only required when you activate the ComfortFlow recirculation mode.

Did you know? You can also program the recirculation pump, so it doesn’t waste energy. It ensures that the unit runs at specific times of the day or when it reaches certain temperatures.

You can do this by

  • Using Navien’s intelligent preheating feature
  • Setting the timer on the optional remote controller
  • Installing the HotButton kit accessories

While the NPE 240A consumes a little more energy than the 240S, there are ways you can program it to use less energy.

Wait time

The buffer tank and recirculation pump in Navien 240A allow it to provide hot water instantly. It does so by eliminating the section of cold water often left in the heat exchanger.  This cuts the wait for hot water and also wastage.

The NPE 240S suffers the cold water “sandwich” effect. Hence, there’s some waiting to do, though not much.

Minimum flow rate requirements

Water heaters have minimum flow requirements to operate. Navien NPE water heaters are no exception.

The “S” models (including the 240S) have a minimum flow requirement of 0.5


But as for the 240A, the minimum flow is less than 0.01 GPM, allowing it to eliminate the minimum flow requirement. Therefore, it provides hot water at a very low flow rate.

Plumbing requirements

NPE 240S works with any standard water heater plumbing system.  But as for the 240A, you’ll have to do additional plumbing for the external recirculation loop. It’s basically a return line that allows hot water to loop back to the water heater.

Optional accessories

Navien has optional kits for NPE 240S and NPE 240A water heaters. However, the 240A has the upper hand. It’s compatible with two extra optional accessories: the H2Air Kit option for space heating and handheld remote control.


Navien tankless water heater cost will factor in the initial cost, labor costs (plumbing and installation), and operating costs.

There’s no significant difference in the operating cost. NPE 240S averages $193 per year, while NPE 240A averages $195 per year.

As for the initial and labor costs, NPE 240A is more expensive, around $3 500. This is due to the extra features (buffer tank and recirculation pump) and additional plumbing for the external recirculation loop. The NPE 240S will cost you $3,050 for the initial cost and professional installation.

Which one to choose: Navien 240A or 240S

So, Navien NPE 240S vs 240A, which one is better? Is it worth the extra money to go with the 240A? Or should you stick to Navien 240 Standard?

Choose Navien 240A if:

  • You have a high budget level
  • You want instantaneous hot water and space heating ( with H2Air Kit)
  • There’s extra space for additional plumbing
  • You have low-flow rate fixtures

Choose Navien 240S if you:

  • Have a medium to high budget
  • Are ok with waiting for hot water
  • Want a unit that can accommodate high flow rates
  • Don’t have extra space for additional plumbing


The Navien NPE-240S and the NPE-240A are both great options for residential water heaters. They’re more efficient than your average tankless water heater. Also, they have a higher heat capacity than other Navien tankless water heaters & boilers.

Well, these two water heater models have a lot in common. However, there are a few key differences that might make one better than the other for your specific needs. For example, if you want a unit that offers instant hot water, NPE-240A is probably better than NPE-240S. On the other hand, if you don’t need as much power or want to save money on heating your water, go with the NPE-240S.