BOILER WATER CHEMISTRY
Boiler Antifreeze ... or Water

Making the choice between just using water in your outdoor boiler or upgrading to significantly more expensive chemicals is no easy decision and requires a degree in Chemical Engineering.

But after 25 years of running an industrial outside wood boiler let me suggest or share with you a few stories, some conditions to consider and some questions for you to ask both to yourself and of your boiler supplier.

This is a five part series covering everything from

  • purpose of the boiler fluid
  • water or should you use antifreeze in your boiler
  • the types of antifreeze, Methanol, Ethylene or Propylene
  • RV, automotive or HVAC antifreeze
  • water chemistry and wood boiler water treatment
  • a list of some of the big boys that make the various forms of boiler antifreeze, inhibitors to prevent corrosion, stop-leak sealers and even refractometer to test chemical concentrations

so lets start ...

The first step in understanding the boiler + antifreeze and/or water conversation is to understand its purpose.

The water or antifreeze for a home boiler is the medium that moves the heat generated by the wood, from the boiler's location in the backyard to some form of heating system inside your home.

Once it gets to the house it can dump into various heating loops from in floor heating to water-air exchangers for forced air systems or standard water radiators or wall mounted registers. In every case air in your home's environment comes in contact with the heated water from your boiler, warms up and subsequently loses heat to warm your home.

The water, having lost a lot of its heat in its travels around your home, now returns to the outdoor boiler to be reheated. It then repeats the cycle, running around your home and back to the boiler in a continuous cycle.

The boiler is designed (if the plans are good) to maximize the contact area where the boiler water wraps around the wood burn chamber to heat it in the most efficient manner possible.

All outdoor wood boilers have a water jacket on the outside and an internal canister mounted on the inside to contain the fire. The boiler water lives in the space between these two jackets keeping the metal burn chamber cool and the water hot. Various outdoor wood boiler plans and brands incorporate more sophisticated designs to increase the contact zones between water and the burn chamber to maximize the exchange of heat.

As an example the more expensive boilers even flow water around the front door cavity to take advantage of the heat from the fire at this location. The boiler antifreeze or water cools the metal of the door at the same time and prevents warpage. A win-win situation.

The more heat it can absorb from the flue gases the less is lost up the chimney.. but it can come at a price but that's discussed in another section. Here we want to focus on the water or antifreeze and the roles and responsibilities it carries for home boilers.

So lets first debate whether pure water is adequate or should you use antifreeze in your boiler.

Main Index:
10 Keys to Buying or Creating the Best Outdoor Wood Boiler Plans