How Do I Winterize My Outdoor Wood Furnace?

How Do I Winterize My Outdoor Wood Furnace?

We received this question from two customers this Fall so we figured we would post a blog article about it. Yes, this is uncommon, but this must be done very carefully…

If you plan to NOT use your outdoor wood boiler this winter, and you want to shut it down for the entire season and protect it, then you maybe asking the question “How do I do this?”, then these are some important things to consider.

First, if you are reading this article, let me congratulate you for your diligence in maintaining your outdoor boiler and making sure it is properly cared for during the winter months, particularly if you are not going to use it.

To answer this question, you have several options. This will depend primarily on whether you will be using your home, or whether the home will be empty for the winter. If the home will be occupied, then the best solution is to winterize the furnace as if you were going to be away for one month.

Those instructions are as follows:

  1. Observe all safety precautions
  2. Allow time for the fire and coals to completely burn out.
  3. Empty all the ashes and lightly scrape out the firebox to remove all ashes.
  4. Fill the system with water until it is completely full.
  5. Make sure the proper outdoor boiler water treatment procedure is followed - THIS IS CRUCIAL! Visit for any needed Liquid Armor water treatment and make sure to send in a water sample. More outdoor wood boiler parts are also available.
  6. Turn OFF the outdoor wood boiler power switch on the front so the fan does not run. If the fan runs without a fire burning in the firebox, it will continuously blow very cold air through your firebox, which will suck heat out of the boiler water! This will cause your indoor heating system to cool your home (instead of heating it) and therefore you will burn a large quantity of expensive fuel to keep the home warm.
  7. Unscrew the light bulb on the front of the outdoor wood stove to save electricity. (Or for GX model furnaces, leave light switch off.)
  8. Flush and clean the filter.
  9. Make sure the chimney cap is in place to prevent rainwater from entering firebox. You can also put a 5-gallon bucket over the chimney if it is properly secured.
  10. If you have a forced air furnace with a second thermostat controlling your indoor furnace blower fan, be sure to turn off the power to this thermostat.
  11. You MUST keep the boiler pump circulating! 
  12. Again, it is critical that the outdoor boiler blower fan and draft remain OFF, and the pump continues to circulate. 

By following these steps, your furnace water will continue to circulate and this will enable the furnace to pick up a trace amount of heat from your home and prevent the furnace from freezing.

You have two other options:

1. Another option is to put antifreeze in your furnace, but that is expensive. Follow the antifreeze manufacturer's recommendations for the desired freeze protection. This is VERY costly and if you ever have to drain your furnace, you have lost the investment. Never use ethylene glycol. You may only use propylene glycol.

You must use a grade equivalent to Dow Frost or Noble No Burst. (RV Antifreeze is not authorized as we have no data to support its effectiveness in this application.) The cost can be more than $30 per gallon, and if you needed 50% antifreeze mix, you would need at least 150 gallons to protect an HE-2100, which holds 300 gallons.

So this cost could be $4500.00 just to purchase the antifreeze alone - not a very good option. Keep in mind that this antifreeze/water mix must still contain Liquid Armor Water Treatment if you choose this option. See our blog article on using antifreeze at our website here.

2. You may drain your boiler and blow out the lines. This is not good for an outdoor wood burning boiler because any steel boiler is never intended to be emptied once it has been filled with water, and left empty for any periods of time, as this could damage the steel.

Outdoor wood burner steel should not be exposed to anything other than properly treated water with an appropriate amount of wood boiler water treatment. The steel must be protected and if drained, it may not be not properly protected.

If you choose this option, you must first add four gallons of Liquid Armor corrosion inhibitor to the furnace before it is drained – THEN ALLOW THIS MIXTURE TO CIRCULATE FOR 24 HOURS, then drain the furnace. Four gallons of water treatment can be purchased at dealer pricing in a Dealer 4-Pack at this link: Water Treatment 4-Pack.

3. Draining out the lines can be difficult without a hi-powered compressor. You may want to hire a lawn sprinkler company to do this as they normally have large mobile compressors and they are equipped to come to your home and do the job quickly.

Protect Your Investment! You are wise to make sure you take the proper steps to protect your outdoor furnace so that you can get many decades of money savings by heating your home with the most cost-effective heating method ever discovered!