How To Test and Treat Your Outdoor Furnace Water

Taking a water sample but out of sample bottles?

-You can fill any 500 ml pop bottle, then download and print a mailing label. After filling out the mailing label secure it to the bottle and send it into HeatMasterSS for testing.

-Download the mailing label HERE


Water has the ability to partially dissolve almost every substance on Earth, including your boiler. But with the right protection and water maintenance, you can fight back.

A key piece of maintenance is regularly testing the water in your furnace’s water jacket so you know how to treat it. In fact, you must test your water at least once per year to qualify for your HeatMasterSS warranty

If you take care of your water, your water (and your furnace) will take care of you. 

Taking a water sample:

After purchasing your outdoor wood boiler, you’ll want to locate your water sample bottles, mailing cartons, and mailing labels that come with your furnace.  If you need additional supplies, contact your dealer. You can also fill any 500 ml pop bottle and download and print a mailing label. After filling out the mailing label secure it to the bottle.

Wait at least 48 hours after adding water treatment and/or firing your boiler before taking a sample. Open your boiler furnace drain located at the bottom rear of your furnace for 10-15 seconds or until the water runs clear. Be careful as the water can be extremely hot and come out with a lot of pressure. Once the sample water is cool, fill one of the supplied test bottles.

Next, complete the mailing label including your email address, model number, and the serial number of your furnace. You will also want to note on the label if your furnace water contains any antifreeze or additional chemicals.

Results can take up to four weeks, or eight weeks if no email address is included. The test will determine if your water is in the recommended operating levels. 

Treating your Water

You will receive a water test report outlining what you should do if your water needs adjusting. 

Treating the water allows us to control the levels of dissolved gases and solids that can cause corrosion, scaling, and damage to equipment. And treatment helps protect everything the system water touches, not just the furnace.

You can add water treatment through the fill pipe located at the top of the furnace when initially filling the furnace with water or after testing. Water treatment may need to be added or your furnace may need to be drained and flushed and water treatment added. If any action is required, operate the furnace with the pumps circulating for at least 48 hours, then take another sample and mail it to the test lab.

 If you have not received your test results within 6 – 8 weeks, please follow up with our office at 877-325-9792 or [email protected].

Remember, because the furnace is an open system, it’s normal that water will have to be added annually. Six to ten gallons is not unusual.

HeatMaster Wood Burning Furnace Water Treatment

Water Treatment Web

To help protect your furnace, we recommend our custom-designed HeatMaster Wood Burning Furnace Water Treatment.

Custom Formulated

The formula was custom designed for wood and coal boilers to create a chemical armor film. This armor contains multiple active ingredients to prevent scale, sludge, corrosion, and oxygen pitting. It also helps to maintain proper pH and alkalinity levels in your water system.

HeatMaster Wood Burning Furnace Water Treatment contains a special volatile corrosion inhibitor that vaporizes into the water vapour itself to help prevent corrosion above the waterline. This provides extra protection wherever water vapor contacts metal surfaces.

Long-lasting year-round protection

The benefits are only lost when the treated water is drained out of the system or diluted by adding water to the system.

Economical dilution rate

HeatMaster Wood Burning Furnace Water Treatment is to be used in systems containing water or antifreeze solutions. The typical feed rate is one gallon per 200 gallons of system volume.

The liquid formula ensures proper mixing with system water and is easily tested so proper residual levels can be maintained at all times.

Effective in hard and soft water

HeatMaster Wood Burning Furnace Water Treatment will not form sediment in hard water and contains proprietary ingredients.

Soft or Hard?

It’s the age-old question: soft water vs. hard water… which is better for your boiler?

Groundwater has percolated through the ground and usually has high levels of minerals. Surface water found in lakes and streams typically has lower amounts of minerals but is high in dissolved gases and suspended solids.

Treated or softened water can often be more corrosive than natural well or surface water, and treatment is designed for slightly harder water.

You need to know the pH level, as boiler water needs to be in an alkaline state. A 7 on the pH level is neutral. Going below 7 you are in an acidic state, above is an alkaline state. However, the pH level is on a logarithmic scale, 8 is 10x alkaline than 7, but 9 is 100x more alkaline, and 10 is 1000x more alkaline than 7.

However, the only way to know for sure is to test the water!

Important Measurements on Your Report:

Conductivity: 100 – 4000 ppm

Conductivity is a measurement of the minerals in your furnace. While it’s common for water to contain minerals, too much can cause problems like scaling and corrosion in a hydronic system.

pH: 8.5 – 10.5

pH is a measurement of alkalinity, which determines whether you have hard or soft water. Again, it’s best for outdoor furnaces to have harder water as the active ingredients in the water treatment neutralize hard water easier than softer water.

Nitrites: no less than 730 ppm

Nitrites are the active units of water treatment available to neutralize harmful elements like bacteria that can build up in the furnace water over time.

End of Season Recommendations

-Make sure your treatment level is in the 800ppm – 1200ppm

-Fill the unit with water until the water comes out the top of the vent opening

-Cover the vent


An outdoor furnace is a long-term investment in the independence and peace of mind your family deserves. Keep your furnace running for decades to come with the right balance of elements in your water jacket by testing it regularly.

HeatMasterss is a family-owned company that has been manufacturing outdoor furnaces for over 20 years. Our mission is simple; help families achieve heating independence and save money.

If you have any questions or want to learn more, we’d love to hear from you today!