BOILER WATER CHEMISTRY:
Wood Boiler Water Treatment

We have discussed whether you should use glycol in your home boiler or just water, and if so what type, but when we talk about wood boiler water treatment that isn't really the issue.

Water treatment is really about making sure that your metal components don't rust away. It is a chemical that is added to your boiler fluid as a "rust inhibitor" for outdoor furnaces that are predominately made of boiler plate, carbon steel or stainless... all metals that can get attacked by acidic ions that develop in the WATER or GLYCOL that resides between the burn chamber and the outside shell.... so I'll repeat ..water treatment is KEY whether you use glycol OR water!

Water treatment is also designed to prevent limescale build up (think of your kettle and hardwater) and biological growth.. as in slime growth that feeds on the organic carbohydrates found in glycol.

It is important to purchase the right water treatment for your wood burning furnace... so here's a few considerations

  • water or glycol? glycols oxidize on exposure to heat creating acids that attack the metal.
  • Type of glycol? Even the brand of glycol, ..where some companies will include their proprietary rust inhibitors premixed into their outdoor furnace glycol.
  • Type of water?

    This might sound kind of dumb but water quality is a BIG issue. Some companies will actually specify the composition of boiler make up water that is IDEAL for standalone use or as a dilutant for their glycol, as it can significantly affect treatment. Their "ideal" definition goes something like this: (varies by chemist)

    less than 50ppm of magnesium and calcium,
    less than 25ppm of chloride and sulfate
    less than 100ppm of total hardness (> than this is considered HARD)

    Numbers higher than these suggested figures will reduce thermal transfer efficiencies as the minerals precipitate out, clogging plumbing and encouraging corrosion. It will also eat up more water treatment chemicals than expected.

    The jury is still out on whether you should use softened water as makeup water. Some suggest the process increases the quantity of chlorides or sulfates in the mix and causes more problems.

    But a recent study by the U.S. Environmental Protection Agency (USEPA) and the American Water Works Association " have both recently corrected their brochures as to the misconception that ion exchange softening has an effect on the corrosivity of water to suggest that ..... softening of water via cation exchange does not make water more corrosive”

    NOTE that there are a number of ways to soften water so this comment is not directed at all water softening technology, but rather only "cation exchange" methodologies.

  • design of the furnace, metals used

    Some rust inhibitor for outdoor furnaces are designed for use in high carbon steel environments and some that mechanics are familiar with are specifically for aluminum engines or radiators (so don't get confused with those on ebay or amazon) ... and some outdoor boilers like the Heatmor Furnace requires inhibitors for their stainless steel interior.

The best I can suggest is this:

  • Have your water analyzed by your local utility to figure out where it fits in this Hard vs Soft continuum
  • Talk to the supplier of your boiler to see if they have a recommended "inhibitor" and provide water analysis as part of their service, many do. It is always better to go with their recommendations as this may suggest a recourse or warranty issue if you do otherwise.
  • If you decide to go the glycol or heat-transfer fluid route, most of these providers are very large companies and DO provide technical support. Use it! They ARE chemist! many of their products are pre-mixed with the right wood boiler water treatment AND come pre-diluted with the right make up water offering a full solution .. so you don't need to even read this material :)

Whatever you do , make sure that you DO use a rust inhibitor or water treatment of some sort, hopefully you can rely on the expertise of your wood furnace reseller. Note that they should do an annual diagnostic as part of their service to see if you need any water treatment top-ups .

For your continued reading I have included a list of some of the better known manufacturers of specially formulated heat-transfer furnace antifreeze and water treatment inhibitors for a home boilers.

Main Index: Antifreeze for a Home Boiler?