Thousands of oil and wood boilers have been converted to burning wood pellets in Europe using the Pellx wood pellet burner over the last decade or more. The Pellx’s design lends itself to easy conversions. Most oil and wood boilers and furnaces can be converted but some can’t and some will work better than others. The boilers minimum combustion chamber dimensions are outlined in the manual. 12” of clearance past the end of the gun is the minimum general rule. More is better, to a point, because too small a combustion chamber will not allow you to have as much heat effect out of the burner without the heat backing up into the burner and causing an automatic shut down. Another consideration is cleanability, too small a chamber will require more frequent cleanings. Typical oil boilers are not designed for much ash accumulation and are not designed for burning solid fuel. When you burn pellets you will produce ash and soot, the amount being dependent on a number of variables, pellet quality being the main one. As the heat transfer surfaces of the boiler get coated with soot and ash their efficiency goes down so it is important to keep those surfaces reasonably clean. I find I need to clean my converted oil boiler after combusting about 700 lbs of middle to low grade pellets. The last cleaning after 700 lbs yielded about 3 lbs of collected ash. More frequent cleanings would make for higher efficiency but also more work. A boiler that is easily opened and is easily cleaned is a better candidate for pellet conversion than one that isn’t. Boilers with more vertical heat exchange surfaces are better than ones with horizontal. Results will vary but as a rule of thumb you are typically going to get 15% less heat out of a given oil boiler when it is converted due to ash accumulation and cycle time of the burner as compared to an oil gun.
If your current system is oversized, as they typically are, you will have better conversion results than a system that is undersized.
ALWAYS CHECK YOUR STATE AND LOCAL CODES BEFORE CONVERATING YOUR BOILER OR FURNACE. Technological change always outpaces bureaucracy change. But, just because thousands of Europeans have successfully converted their oil and wood boilers in accordance to their fire, safety, and emission codes doesn’t mean you are necessarily allowed to in your state. Every state and local authority has different codes for boilers and solid fuel burning appliances. Some state boiler codes will not sanction a conversion. As with building codes, different insurance companies will provide different types of coverage too. On conversions, some of the installations have been totally covered and while some have only been able to get coverage as a secondary heat source. CHECK WITH YOUR INSURANCE AGENT ON YOUR PARTICULAR POLICY.