What You Need To Know About Water Treatment for Your Wood Boiler

Outdoor wood boilers offer an alternative heat source that is appealing to many homeowners looking to save money on heating costs. The investment can save you thousands, but it is important to know what you can do to ensure the longevity of the system. If maintained properly, a wood boiler can last 20 years or more and give you a return on your investment many times over.

One of the most important and often overlooked steps to maintaining a wood boiler is treating the water that flows through the system. When steel is exposed to oxygen and moisture, a chemical compound called Oxide is formed and creates rust. If left untreated, further damage can result in the form of corrosion, pitting and eventually cracks in the water jacket.

The sample bottles below show the effects of untreated water after just 24 hours. As you can see, the corrosion process begins almost immediately and damage to the system is inevitable unless proper treatment procedures are put in place.


To prevent corrosion, you must treat your water with a rust inhibitor. Control Chemical is a rust inhibitor that provides a protective barrier, prevents the breakdown of metals, and keeps minerals like Calcium and Magnesium in check. Treatment must be added to the wood boiler upon installation and annually thereafter.

The amount of chemical to add to your outdoor wood boiler depends on how many gallons of water your system holds. One gallon of Control Chemical treats 200 gallons of water. You will want to use this ratio after installation and any time after you have drained and refilled the water in your wood boiler. For annual treatment, use a quarter of the amount used for initial treatment. For example, the Crown Royal RS7400 model holds approximately 400 gallons of water. This means for your initial treatment you will use 2 gallons of Control Chemical and as long as you do not drain your system, treat with ½ a gallon annually.

To maintain the 20 Year Warranty on your Crown Royal wood boiler, it is required that the water in your system is tested annually. After installation, follow the procedure outlined on the Water Treatment page of our website. You can also access a printable version of the test kit mailing label on the Water Treatment page. Our third party testing facility will test the water for three items:

  • Conductivity – Measures the water’s ability to carry an electrical charge. Water impurities such as metals increase water’s conductivity. A conductivity level of 6 or less is required.
  • PH Level – The PH measures how acidic the water is. This is a good indicator of whether the water is hard or soft. Pure water has a PH of 7. A PH level lower than 7 indicates the water is acidic (soft water), and above 7 indicates the water is basic (hard water). Acidic water carries higher levels of toxic metals and leads to premature damage to the water jacket and metal piping. A PH level between 8 and 14 is satisfactory.
  • Nitrite Level- Sodium Nitrite is an active ingredient in Control Chemical that reduces the oxygen level of the water and prevents rust. A minimum of 900 PPM must be present in the water sample.

By treating and testing your water annually, you can increase the longevity of your wood boiler. Crown Royal Stoves are built to last, and we are always here to assist you with any questions you may have along the way. If you have any questions about treating or testing your water, call us at 1-866-361-7355.