All outdoor furnaces are built on the same principles. They burn fuel, heat water, and transfer heat into the home. Sounds pretty simple, right? Well in theory, that is correct, but when it comes to how the furnaces burn and operate, it is a little more complex than that. As you read on I will explain the differences of what we have found in comparing some of the different models out there on the market.
Let’s start with the appearance of the furnace – the housing. As you have probably seen during your shopping for an outdoor furnace, there are many different styles and designs to choose from. Some on legs, some on concrete pads, some housed in nice looking buildings, and some that look like a shiny tool box in the yard. Let’s start first with the furnaces on legs or skids. At first glance you can see where the problems lie with these furnaces. First of all, your piping and plumbing is easily expose to the weather, sunlight, and critters. Second, the cool air and snow that blows under the stove will help cool down that furnace, causing you a greater wood consumption. The better choice is a furnace that is sitting flat on a concrete pad where your piping is protected by the housing, and the heat loss is very minimal from below the furnace.
Next, we will look at the housing and insulation of the furnaces. There are a lot of different types of housings used for protecting the boiler of the outdoor furnace. Most of them will work well, but there are a few things to look at when comparing furnaces. First thing to look at should be, is the furnace fully insulated? Meaning, are there places of heat loss other then the chimney? Most outdoor furnaces have their firebox door exposed on the outside of the housing. This works great for ease of access, but fails when it comes to heat loss. Suggestion, find a outdoor furnace that has double door design to trap the heat inside the furnace, instead of heating the outside air and burning more wood. Now the big questions is what type of insulation is used on the furnace and what’s the real difference? Well lets get started on the two main types of insulation in outdoor furnaces, urethane foam insulation and fiberglass insulation. What we have found is that most people don’t realize the differences in the insulation, so let me explain them to you. Urethane foam insulation is the type of insulation that is sprayed onto the stove and forms an air tight seal to the stove. It has a great r-value for insulating the furnaces but has a quick drawback that most people overlook. It is flammable. Other draw backs to the sprayed on urethane insulation is when there is a problem with the furnace, there is no easy way to find it without cutting all the insulation off (not something I would want to do or pay to have somebody do $$$). Now with the fiberglass insulation, it is the blanket type insulation that you put in the walls and ceilings of your house. You do lose some of the r-value with the fiberglass insulation compared to the urethane, but the fiberglass makes up for it being a noncombustible material that can be easily removed from the furnace to see and repair any issue that may occur.
Personal suggestion: Find and outdoor furnaces that sits flat on a pad, which is fully insulated, and uses a noncombustible material for insulation like fiberglass.
Please stay tune for more on outdoor furnaces.