Engineer's Product Breakdown: Tankless Hot Water Heaters

Here is a guide of our top commercial choices for property owners and managers of multi-unit facilities. Especially for 10-50 units, housing approximately 25-125 people.

Tankless Hot Water Heaters for Multi-Unit Buildings

Your Engineer
Jennifer Kuether-1
Jennifer Kuether
Tankless water heaters are becoming a more attractive alternative for property owners and managers than traditional tank water heaters. Since tankless water heaters only heat the water on an as-needed basis as opposed to the traditional tank water heater which continually heats the water until needed, tankless water heaters are more energy efficient.

The Complete Guide To Tankless Hot Water Heaters

Traditional water heaters are big and bulky some reaching over six foot tall with a two foot base and weighing over 500 pounds. While the average tankless water heater is compared to a small suitcase and weighs in around 100 pounds. This factor also benefits the environment by taking up less space in landfills.

Tankless water heaters are fueled by gas, propane, or electric. However, the first part of this guide is about commercial products only gas or propane tanks are discussed. The second part of the guide will discuss a residential type of systems with electric units discussed there.

Best In Class


Noritz NC380 SVNG Indoor/Outdoor Tankless Water Heater



  • No Pilot Light to Maintain
  • Energy Efficient
  • Condensing Appliance
  • Stainless Steel Casing
  • Energy Star Certified
  • Durable


  • Expensive
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The Noritz NC 380 Series is the best commercial gas powered tankless heater on the market. This unit can handle large heavy duty demands of apartment complexes. Each unit can produce a flow rate of 13 gallons per minute (gpm) and 24 units can be connected with a single system controller. That is the equivalent of 316 gpm.

✔ Stainless Steel Casing
✔ ASME Accreditation
✔ Natural Gas (NG) or Propane (LP)
✔ Thermal Efficiency 84%
✔ Indoor/Outdoor Use
✔ Copper Heat Exchanger
✔ Digital remote included
✔ 100° - 180°F Temperature range

The Noritz NC 380 Series heaters run more efficiently than a traditional water heater. This water heater is a fully condensing appliance. Which means it captures heat from the exhaust gas and uses it to preheat the incoming cold water as it passes through the heat exchanger, in the process, being energy efficient.

Top Mid-price Pick

Rheem Heating Chambers RTEX-13 Residential Tankless Water Heater

Rheem Heating Chambers RTEX-13  Residential Tankless Water Heater



  • 99.8% Energy Efficient.
  • Simple Installation.
  • Multiple Application or Single Point-of-Use.
  • Mid-Price Range.


  • Non-ASME Certified
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The Rheem Professional Classic tankless electric water heater offers continuous hot water quickly and on demand for multiple applications or used as a single point-of-use heater.

Rheem Manufacturing Company in Emeryville, CA was founded in 1925 by brothers Richard and Donald Rheem. Through the years, the company has produced numerous amounts of products. Currently, Rheem produces heating, cooling, water heating, pool & spa heating, commercial refrigeration products, and one of the latest markets is the tankless water heater.


✔On demand endless water.

✔Compact and stylish.

✔99.8% Energy Efficient.

✔Simple Installation.

✔Digital temperature display.

✔External controls to adjust temperature in 1 degree increments.

✔5-year limited warranty.

✔Multiple Applications or Single Point-of-Use Heater.


Everything we recommend

Best ECONOMY Option


Rheem RTGH-84DVLN-2 Natural Gas Condensing Tankless Water Heater



  • Energy Star Certified
  • NSF Certified
  • Eco Friendly
  • Budget Friendly


  • Non-ASME Certified
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Rheem’s revolutionary new exclusive performance features include:

  • Water Savings Setting, when activated, decreases the water flow through the pipes until the water reaches the desired temperature. This setting saves the average home up to 1,100 gallons of water per year.
  • Industry Leading Low Flow Activation technology ensures a user will receive hot water in low demand situations.
  • Recirculation Pump Kit-Ready saves up to 12,000 gallons of water per year by recirculating the hot water from the unit through the plumbing providing hot water at the faucet.  
  • Hot Start Programming keeps the unit in a ready-fire state for back-to-back hot water needs minimizing cold water burst.

Upgraded venting includes 2” venting with band connections and now can vent up to 150 feet with 3” PVC and 60 feet with 2” PVC. Plus, a gas line compatibility of ½” up to 24 feet.  




✔ Built-in Condensate Neutralizer

✔ Self-diagnostic system for easy installation and service

✔ High-altitude capability - up to 9,840 feet elevation above sea level 

✔ Pre-wired Digital Remote Control with 10 feet of thermostat wire included

✔ Indoor models require a 120-volt power cord



✔ EcoNet Enabled -  Connect to the EcoNet mobile app via Tankless EcoNet Accessory Kit

✔ Link Multiple Units to operate as one system

✔ 2 Units using the EZ Link Cable

✔ Up to 6 units using MIC-6 Control Board

✔ Up to 20 units using MIC-185 plus MICS-180 manifold control assembly--once manifolded the 20 units balance the workload as a system

✔ Multiple Units work together to create redundancy--if one tank goes down the other tanks continue to work 

✔ Maintenance Notice Setting - Optional Feature that Alerts homeowner, to schedule a service check after 500 hours 



✔ Overheat Film Wrap - provides industry best side-to-side clearance of 1/2 inch and prevents overheating

✔ Freeze protection to -30°F by using ceramic heaters and copper tubing

✔ Water and Gas leak detection

Best luxury option

AO Smith ATIO 910 AN

AO Smith ATIO-910-AN



  • Energy Star Certified
  • Electronic Ignition


  • Expensive
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AO Smith claims to be the leader in innovation when it comes to tankless water heaters.  The ATIO 910 Series was designed specifically for heavy-duty commercial applications. These fully modulating, gas-fired, tankless water heaters with optional sealed combustion and power vented flue, can be installed either indoors or outdoors.  

Capable of supplying hot water for domestic hot water systems (directly or indirectly) using water storage tanks, recirculations systems, hydronic heating systems, radiant floor heating systems, and/or combined domestic & heating applications (local codes dictate proper compliance). 


✔ Commercial Grade Copper stronger resilience against erosion

✔ Continuous Maximum flow rates up to 14.5 GPM

✔ Easy-Link up to 4 units

✔ Multi-Link up to 20 units with TM-MC01 (no multiple controller needed)

✔ Natural Gas (NP) or Propane (LP)


✔ 5-year limited warranty on heat exchanger in commercial applications 

✔ 5-year warranty on all parts


✔ Built-In Freeze Protection

✔ Manual Reset Hi Limit (Set at 194°F)

✔ Overheat Cutoff Fuse

✔ Constant Temperature Monitoring

✔ Air Fuel Ratio Rod

✔ GFI, Fuse & Surge Absorber

✔ Flame Sensor


✔ 5” Category III Stainless Steel

✔ Vertical or Horizontal Installation

✔ Power Vent

✔ Electronic Ignition - No Pilot Light

Additional Considerations

Do tankless water heaters work?


In order to use this guide you must fully understand how tankless water heaters work. But first for comparison reasons, let’s discuss how a traditional hot water heater works. A traditional water heater has a large tank that holds and heats the water. The tank continually heats the water to a constant temperature to be ready when the faucet is turned on. Since a traditional heater system keeps the stored water heated, they waste a lot of energy.


In contrast, tankless water heaters only heat the water as needed. A tankless water heater senses the water flow, usually 0.5 gpm, but each system varies.  When the minimum flow rate is reached the system ignites, water flows into the unit, the heaters kick in and flash-heat the water as it flows through the heat exchanges.  Since there is no standby heat loss, the savings can amount to 40%.  


  • The big question is, are tankless water heaters worth the investment for your rental units?  Here are things to consider, when making that choice.  

On-Demand hot water vs. Lag time


After the “standby heat loss” the systems do as promised and deliver instantaneous hot water.  Tankless water heaters are equipped with a heat exchanger that delivers heat from one element (or coil in some units) to another.

The downside to the tankless water heater is that the water doesn’t come straight out of the faucet hot because the cool water that is already in the pipes will need to be released before the hot water will begin flowing. So, there is still a wait time to receive hot water, but once it starts flowing, it is an endless supply.

Endless supply of hot water vs. hot water Inconsistencies

Ever been last in line to take a shower? Chances are your shower was lukewarm or possibly even cold. A tankless water heater is supposed to solve the problem. The whole concept of tankless water heaters are to be on-demand heaters. So, they’ll provide you with hot water when you need it usually just enough power to heat the amount of water needed at that time.

On the other hand, the amount of hot water simultaneously can drastically impact water temperature causing fluxuations. The size of your system and your hot water demands will determine how many showers may be taken or other appliances running simultaneously.  

Longevity vs. The investment 

Tankless water heaters are built to last twice as long as a traditional tank system. While a quality tank system normally needs replacing every 10 to 15 years, tankless heater systems are designed to last 20 to 25 years, this is saving money over decades of use.  

The upfront initial investment have deterred many building managers and owners from updating their systems. Some think that saving money over decades does not justify the investment.  Remember it isn’t just the cost of the tank involved, the more intense labor results in higher installation cost.

Space savings vs Innovations


A major benefit is the size of tankless water heaters compared to tanked heaters. These space savers free up precious floor space in basements of apartment buildings. 

Depending on location, many tankless systems need a water softener.  This may eat away at the saved space from the heater.

Environmentally friendly vs luxury

The obvious environmental advantage is the energy savings. However, today’s gas tankless water heaters have virtually zero emissions and are environmentally friendly.  Most models use low NOx technology to keep emissions low.

While tankless systems are definitely more, “green” than the tanked counterparts, the benefits are more collective than personal.

Longer warranty vs warranty stipulations

Tankless water heaters are designed to outlast traditional heaters and so the warranty is last longer.  Some warranties will offer full replacements making it a desireable option.

However, most warranties will become void if certain stipulations are not met. Such as--adhering to a maintenance schedule, adding a water softener system or an annual cleaning.  These are added cost to factor in when deciding on a tankless system.    

Condensing Vs. Non-Condensing


A condensing Tankless Water Heater extracts the exhaust gases and uses it to preheat the incoming cold water as it passes through the heat exchanger.  

Whereas, a non-condensing water heater push the exhaust gas outside to vent. These gases are around 300°F so special non-corrosive materials are needed for the pipes to withstand these temperatures. These materials are often very expensive.  

No Fear of Flooding

Although tanked heaters have a possibility of a ruptured tank and flooding the area it is located, tankless heaters does not have a tank to rupture. Therefore, easing the fear of flooding.  

For apartment managers and property owners tankless hot water systems can help reduce operational costs and save property owners money in the long run.  

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