Paloma PH-20 Water Heaters 
from the 5.3 Series

Paloma PH-20 outdoor tankless water heater

A review of Paloma water heater 5.3 / PH-20 series. Paloma 5.3 models use tankless technology to provide instant water heating for residential use, on-demand, and in an endless supply.

Built as the direct vent models for indoor and outdoor installation, these tankless and gas-powered water heaters are high efficiency and Energy Star compliant.

Models review

With respect to venting options and installing location, Paloma 5.3 water heaters can be found as:

  • PH-20RDVSN - indoor direct vent model powered by natural gas
  • PH-20ROFN - outdoor model powered by natural gas
  • PH-20RDVSP - indoor direct vent model powered by propane gas
  • PH-20ROFP - outdoor model powered by propane gas
  • PH-20R DVSN(P) (P for propane) with direct venting option
  • PH-20R OFN(P) for outdoor installation
  • PH-20R IFSN(P) for indoor installation

Features and benefits

Flow rates

All the tankless models from the Paloma 5.3 series have 145,000 BTU/hr gas input, with a maximum supply of 5.3 gallons per minute, or up to 223 gallons per hour (with 64 F (18 C) rise). These numbers are calculated for southern, warmer areas (Sunbelt), where the incoming cold water temperature is 60 F (16 C). In northern and colder regions, where incoming water is 40 F (4 C), the supply is less than 4 gallons per minute.

With the above flow rates, Paloma water heaters can provide enough hot water for up to two simultaneous showers and supply small size residential homes, condos and apartments.


Paloma water heaters from the 5.3 series can use both natural gas and propane for domestic water heating but are not intended for space heating applications.

They also require 120 VAC to run electronic components (blower, a diagnostic system, electrodes...).

Power and efficiency

Every Paloma water heater 5.3 is considered a high-efficiency unit with an energy factor of 0.82. The heater's thermal efficiency of 82% is achieved through intelligent electronic controls, also designed to provide high safety for the unit and users.

A modulating burner allows adjustable thermal output, depending on the water flow and temperature.

Indoor models can provide power between 21,600 and 145,000 BTUs/hr for natural gas, with the maximum power of 141,000 BTU/hr for LP gas.

The outdoor models works between 21,600 and 141,000 BTU/hr, while direct vent models operate between 21,600 and 141,000 BTU/hr for natural gas and 135,000 for propane.


In order to start and protect the heater at the same time, the minimum cold water flow has to be met, which is 0.66 gallons per minute with a minimum pressure of 14 psi.

At the same time to prevent inner parts from malfunctioning, the maximum allowed water pressure is 150 psi. This is why the TPR valve must be installed and operate properly, protecting the unit from excessive pressure.

Temperature adjustment

Maximum hot water temperature is factory-set on 120 F (49 C), but it can be adjusted to up to 140 F (60 C) by using the MAIN (UMC-117) remote control or dip switch adjustment.

Venting options

Indoor models

Paloma water heater 5.3 PH-20R IFSN is an indoor model that must be installed inside only. For the proper and safe work, proper venting material has to be mounted on the unit, with a termination suitable for Category III venting.

Indoor models use the one-pipe system, 3" in diameter, to discharge the flue gases out, UL approved, and Category III stainless steel. The air for gas combustion is used from the inside.

Fresh air must be supplied through the provisions that comply with local codes and standards, either from the outside or other room. Venting pipes can be run horizontally or vertically and with an adequate termination.

Outdoor models

Paloma water heater 5.3 PH-20R OFN has to be installed outside only, but not inside or in manufactured (mobile homes) and any other position except vertical.

Due to freezing outside temperatures, the recommendation is to protect your tankless water heater, both hot and cold water lines, with proper insulation. Venting is not required for outdoor installations.

Paloma water heaters with direct venting - PH-20R DVSN, must be installed with a 3/5" diameter, UL approved and Category III coaxial stainless steel vent pipe, installed horizontally or vertically and with proper termination. It is not designed to install outdoor, mobile homes, bathrooms, or any occupied rooms that are usually kept closed.


Paloma 5.3 models can be connected to another unit into the DUO system to gain even more power by installing it in the manifold system using a DUOnex Cable. Combining its power, the first hour delivery will reach great 360 gallons, while a 100-gallon tank type water heater will have only 135 gallons max.


In this case, water piping must be in "Parallel." The main remote control connected to the manifold controller (MIC-180) will have priority over the one connected to the water heater.

Heaters from the 5.3 series use an ignition device that automatically lights the burner and eliminates the need for the pilot light while reducing energy waste.

All electronic components are connected to the computerized self-diagnostic program and error code display, which helps in troubleshooting and repairs.

Using the manufacturer's manual and error code that appears on the unit, like: 11, 12, 15, it becomes easy to troubleshoot, but professional assistance is recommended.

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