3 Rules For Antifreeze Use In An Outdoor Furnace System

3 Rules For Antifreeze Use In An Outdoor Furnace System
Should I Use Antifreeze?
3 Rules For Antifreeze Use In An Outdoor Boiler


Many outdoor wood boiler owners ask the question “Should I put antifreeze in my outdoor wood boiler?”

The answer is almost always the same – “NO!”

Why not? 3 Simple reasons:

  1. You most likely don’t need it – but see the exceptions below.
  2. Antifreeze is very expensive. We are burning wood to save money, right?
  3. Antifreeze reduces your efficiency by approximately 13 percent.

Normally, freezing the water in an outdoor wood burning boiler can be avoided by doing the following things: (i) have a friend put wood in the boiler and keep it running, or (ii) keep the pump running and allow the forced air system to back feed some heat into the circulating boiler water.

But, if you will be away from the outdoor boiler, or cannot continue to use the boiler, antifreeze may be your best option. You may also have health issues or in rare cases, you face the risk of having no electricity for an extended period of time – these are also considerations.

If you do use antifreeze, remember these three rules:

1. Antifreeze as boiler water treatment? NOPE! This is the most important point and is often misunderstood – even if you use antifreeze, you must STILL use Liquid Armor water treatment. This boiler chemical (corrosion inhibitor) that you would apply to your furnace water coats the inside of the furnace to reduce the effects of corrosion on the metal. 

Antifreeze is NOT a substitute for an outdoor boiler water treatment and will not protect your boiler from corrosion. Remember the rule: “Always keep your boiler full of properly treated water!” Always use Liquid Armor water treatment!

2. Which type of antifreeze is best? You MUST NEVER USE automobile antifreeze, also known as ethylene glycol – never, period. This is a toxic product, it will void your warranty, and you must never have this in your home. (If you have used this in your outdoor wood burner, remove it immediately and dispose of it properly.) 

You may only use food-grade propylene glycol. Do not use RV antifreeze – that is intended only for toilets and drains. You will need to use a concentrated propylene glycol product similar to Dow Frost or Noble NOBURST. Click HERE for info on NOBURST. Also, remember that some brands of antifreeze need to be periodically recharged. Use only high-quality propylene glycol!

3. How much antifreeze is needed? We cannot say because you must FOLLOW the antifreeze manufacturer’s recommendation for how much antifreeze to use, according to the freeze protection you need.

Some antifreeze products will give you freeze protection to 10 degrees at 40 percent mixture, some products will give you freeze protection only to 20 degrees with 75 percent mixture.

So since every product is different, and your needs for freeze protection will depend upon where you live and the circumstances of your installation, follow the manufacturer’s guidelines!

A customer once called and said that his pipes were frozen, but he had used antifreeze? We asked how much, and he said that he thought 15 percent would be sufficient.

Obviously, it was not, and when he checked the manufacturer’s recommendation, he found that their solution could not provide him the freeze protection he needed unless he had a 60 percent mixture in his water jacket.

For more information on this topic, see our blog article “I am NOT using my outdoor furnace this Winter, how do I winterize my outdoor wood furnace?

Please feel free to send us your comments and feedback to care@outdoorboiler.com or contact us. You can also visit our online store OutdoorBoiler.com to browse for more outdoor wood boiler parts!

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One of the most important steps in prolonging the life of your outdoor wood stove is to ensure that the water in your boiler is not corroding the steel. Water starts to eat holes in steel immediately upon contact (through rust corrosion) unless properly treated. So send in your water sample. We test your outdoor furnace water for free!