Paloma PH-25 Tankless Water Heaters from the 6.6 Series

Paloma PH-25

There are two Paloma tankless water heaters from the 6.6 series (PH-25) that we will review in this article. Both tankless models are designed for residential use, provide instant, endless hot water and when you need it. Paloma 6.6 gas models are highly efficient and "green" with low NOx gas production using the latest engineering technology.


Paloma tankless 6.6 can use both natural gas and propane (LP) for domestic water heating but is not intended for space heating applications.

With respect to venting options and installing location, Paloma tankless 6.6 water heaters can be found as:

  • PH-25RDVSN - indoor direct vent model powered by natural gas
  • PH-25ROFN - outdoor model powered by natural gas
  • PH-25RDVSP - indoor direct vent model powered by propane gas
  • PH-25ROFP - outdoor model powered by propane gas

Features and benefits

Power and capacity

Paloma tankless 6.6 series with 180,000 BTU/hr gas input provides a maximum of 8.4 gallons per minute, or up to 278 gallons per hr (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) and the supply is less than 5 gallons per minute.

The heaters can provide enough hot water for up to two simultaneous showers and supply small size residential homes.

Efficient and smart

Both 6.6 series tankless models can work with a maximum gas input of 180,000 BTU/hr and are considered high efficient water heaters as the energy factor is 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.


In order to start and protect the heater at the same time, 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. The TPR valve, which must be installed, is designed and tested up to that pressure.

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

Modulating power

With a gas modulating valve, Paloma 6.6 tankless water heaters can adjust their power based on the water flow demand and temperature, and work in a range from a minimum of 11,600 to the maximum of 180,000 BTU.

Adjusting the temperature

Maximum hot water temperature is factory-set on 120 F (49 C), but it can be adjusted to up to 140 F (60 C) for residential models by using the MAIN (UMC-117) remote control. For natural gas models only, if the heater has to be installed above 3280 ft or 1000 m, the DIP switch adjustment is required.

Venting options

Paloma tankless PH-25ROFN as an outdoor model cannot be installed indoors or in manufactured (mobile homes) and any other position except vertical. Due to the negative influence of cold weather and freezing temperatures, the recommendation is to protect your tankless water heater, hot and cold plumbing lines with proper insulation.

There is no venting required for outdoor installation.

Paloma direct vent water heaters, PH-25R DVSN, must be installed with a 3"/5" diameter, UL approved, and Category III coaxial stainless steel vent pipe horizontally or vertically run and with proper termination. It is not designed for installation outdoor, mobile homes, bathrooms, or any occupied rooms, usually closed.

DUOnex for more power

Paloma tankless 6.6 water heater can be connected to another unit to gain even more power by installing it in the manifold system using a DUOnex Cable. According to the specs and some reviews, the first hour delivery rate will reach terrific 480 gallons when combining the power, while the 100-gallon tank type will have only up to 135 gallons.

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.


Safety features like the ICAD safety system and Overheat limiter Wrap including their benefits can also be found in our review about Paloma.

Tankless 6.6 models use an ignition device that automatically lights the burner and eliminates the need for pilot light while reducing energy waste. It is very easy to use, and together with a built-in electric blower, it contributes to rising the thermal efficiency.

The electronic Paloma tankless 6.6 components are connected to the computerized self-diagnostic program and error code display, which helps in troubleshooting and repairs.

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