Today, taking care of the environment is essential. One of the things that harm the environment is something called nitrogen oxides or NOx. These are harmful gases from burning fuel in water heaters, furnaces, boilers, and cars. The worst type of NOx is nitrogen dioxide or NO2, which is terrible for the environment and can make people sick.

To deal with this problem, the Environmental Protection Agency or EPA makes rules. These rules determine the amount of NOx released into the air. This is why picking the right heating equipment, like water heaters, is essential.

In this blog post, we will discuss why knowing the difference between Low NOx and Ultra Low NOx water heaters matters when you want to buy one.


The Impact of NOx Emissions:

Before discussing the differences between Low NOx and Ultra Low NOx water heaters, let’s first understand why NOx emissions are a big deal. Nitrogen oxides (NOx) can cause many problems for the environment and people’s health. These problems include:

1. Respiratory Problems: 

NOx can worsen breathing problems and cause asthma and other lung issues.

2. Low Water Quality:

NOx can pollute water sources, making the water we drink unsafe and harming the animals and plants that live in the water.

3. Ground-Level Ozone:

 NOx plays a crucial role in forming ground-level ozone, a major component of smog, which can harm human health and the environment.

4. Acid Rain and Smog: 

NOx contributes to the formation of acid rain, which harms plant life, aquatic ecosystems, and buildings. Additionally, it contributes to the formation of smog, reducing air quality.

5. Global Warming: 

NOx is a greenhouse gas that contributes to global warming and climate change.

6. Toxic Chemicals: 

NOx can react with other pollutants to create toxic chemicals that harm human health.

Given these severe implications, reducing NOx emissions from heating equipment is paramount.

Choosing the Right Water Heater:

When purchasing a new water heater, making an informed choice to minimize NOx emissions is crucial. Two main categories of water heaters are available for consideration: Low NOx and Ultra Low NOx. To determine which one suits your needs, consider the following factors:

1. Energy Output:

Water heaters are rated based on how much energy they use. Manufacturers usually measure this rating in joules for each amount of NO2 they produce (measured in nanograms). Check the energy efficiency to ensure it doesn’t create a lot of emissions.

2. Capacity and Size: 

Choose a water heater that matches your household’s hot water needs while considering it also fits in your space.

Differences Between Low NOx and Ultra Low NOx Water Heaters:

The primary distinction between Low NOx and Ultra Low NOx water heaters lies in their emissions and technology:

Low NOx:

  • Emissions: Low NOx water heaters can reduce NOx emissions to as low as 30 parts per million (ppm).
  • Technology: They use Flue Gas Recirculation (FGR) and maintain 3 to 5% excess oxygen with strict guidelines.
  • Turndown Ratio: Turndowns are typically less than the ratio of 8:1.

Ultra Low NOx:

  • Emissions: Ultra-low NOx water heaters achieve emissions as low as 7 to 15 ppm.
  • Technology: They employ FGR, adjusted fuel/air ratios, and staging to achieve minimal emissions.
  • Oxygen Levels: Ultra-low NOx heaters can maintain oxygen levels between 5 to 9%.
  • Turndown Ratio: Turndown ratios are typically 4:1 or 3:1.
  • Continuous Improvement:  Ultra-low NOx technology keeps improving to work even more efficiently.


When buying a new water heater, you must know the difference between Low NOx and Ultra Low NOx. Picking the right one gives you hot water when needed and helps make the air cleaner and healthier by reducing bad NOx. Ultimately, getting the right water heater is a step toward improving the world by dealing with the problems NOx causes for our health and the planet.

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