We have a lot of people asking us how to best determine the proper size or output of a wood boiler for their home. There are a bunch of things to consider when sizing a wood boiler – home insulation, interior/exterior temperatures, wood type/quality to name a few.
Avoid a Common Mistake
One of the common mistakes made when determining the BTU or energy required to heat your home is to look at your current boiler or furnace. Often people look at the sticker on their current system, indicating its size. However, it is possible that your previous heating system was inaccurately sized. By using this approach, you are banking your future comfort on the accuracy of the installer who originally sized the equipment. It also neglects any adjustments or improvements you made to your home – insulation, windows, and leak repair, etc. Primarily, your energy requirement is determined by the square footage of your home, the quality of your insulation, the type of wood you’ll be using for your boiler, and of course the temperature of your region.
The Perils of Oversizing a Wood Boiler
One of the most common techniques used in traditional wood boiler sales is that, ”Bigger is Better” – WRONG! Today’s modern wood boilers, like the Greenwood® Frontier CX, actually work best when it’s working its hardest—if your boiler is operating far below its capacity for most of the year, it can lead to a host of problems. It won’t burn as efficiently, meaning it will produce more smoke and creosote. This means you’ll need both more wood and more frequent cleaning – both ash removal, internal heat exchanger and your chimney. An over-sized boiler also leads to corrosion and other maintenance needs, not to mention it takes up more space in your home. In summary, you lose money not only on the initial purchase of an over-sized boiler, but also through continually wasted fuel and damage.
Rule of Thumb on Boiler Sizing
If you have followed John Siegenthaler, a wood boiler hydronics guru, he strongly advocates to size your wood boiler to 60-80% of your peak demand. The peak demand is the energy your home needs during the coldest week or two of the winter. More than 80 percent of the time, you’ll only be using ½ of your heating system’s capacity. Therefore, to achieve the best annual performance (including spring and fall with warm days and cool nights!) and save you the most money on your annual energy bill, it is best to follow Siegenthaler’s advice and purchase a wood boiler that is sized to cover 60-80 percent of your home’s heat load. There will, on average, be about ten or fewer days per year when your system will not meet your needed usage, but this just means you’ll either have to compensate with your existing system or just re-load the appliance with wood more often.
What to Expect with a Greenwood®
On your average heating days, you’ll probably only need to restock your boiler every 10-14 hours, but on those extremely cold nights you might need to load it more often. See the following chart to gain a better appreciation of what to expect with a Greenwood Frontier CX in your home.
