THAT. IS. BAD. Absolutely, 100% NOT a good idea.
Here are 3 reasons why:
Here's a quick fun fact: did you know that any kind of wood, even properly seasoned (dried) wood still contains at least 25% water? Unseasoned wood contains up to 50% water.
So what do you think happens when wood burns? That moisture it contains becomes steam. When it burns in your furnace, that steam exits through the chimney, (or tube, in the case of a Gasification furnace). HOWEVER, if the water temp is less than 140 degrees, that steam will condense inside the furnace walls, creating a BIG mess.
Conversely, if the water temp is above 140 degrees, the steam will exit the chimney harmlessly.
Just in case you aren't familiar with this term, (and if you take the advice of this article you won't have to be) creosote, by definition, is a mixture of smoke and water residue, a sticky black tar-like substance.
Let me put it this way: creosote is to a furnace chimney or tube as plaque is to a human artery. Allow it to build up, and, well, you get the idea.
Thus, keeping your furnace heating the water at a minimum of 140 degrees is crucial to preventing creosote build-up.
Plain and simple. When condensation forms it nourishes creosote, which ultimately reduces heat transfer. The heat from the fire normally passes into the water in your water jacket through the steel walls - but if those steel walls are covered with a thick layer of creosote, heat transfer, and therefore efficiency, is reduced.
If you want to not only avoid steam and creosote issues with your furnace, but make sure its general functions are running smoothly, always be aware of its temperature. Remember: 140 degrees. That's the magic number!
So to sum up, the 3 reasons you should always operate your furnace at temps above 140 degrees are 1. To prevent moisture condensation, 2. Condensation leads to creosote build up, and 3. Creosote buildup reduces heat transfer and thus lowers your efficiency. This means you will burn much more wood than you need to (and excessive creosote will ultimately kill your furnace, regardless of which furnace brand you own).
The good news is that Hawken furnaces, in normal operation, don't have creosote issues. Just make sure you burn seasoned wood, and follow proper operations and maintenance procedures (see owners manual), and you will enjoy years of warmth and saving big money with your Hawken furnace!
Posted by Alex Walborn - Hawken Energy Outdoor Wood Furnaces