Paloma Tankless Water Heaters PH-25
(6.6 series) 
Review and Buying Tips
(updated 2018)

Paloma PH-25

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


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

With the respect of 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 are able to 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. Heater's thermal efficiency 82% is achieved through the 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, maximum allowed water pressure is 150 psi. TPR valve, which must be installed, was 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 heater adjusts its power, based on the water flow demand and temperature, and it can work in a range from minimum 11,600 to 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 MAIN (UMC-117) remote control. For natural gas models only, if the heater has to be installed above 3280 ft or 1000 m, the adjustment of the DIP switch 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 a 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, when combining the power, the First Hour hot water supply will reach terrific 480 gallons, while 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 ICAD safety system and Overheat limiter Wrap and what are their benefits can also be found in the article about Paloma water heating.

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

All of 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.

Using the manual and error code on the unit; like 11, 12, 15, it is easy to troubleshoot (valve is not open, low water flow, low gas pressure...) and how to repair it (open the faucet to increase the flow, or call the service).

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