Comparison Of Outdoor Boiler Design Features

Other brands of outdoor furnaces use some, or all of the below listed features in their various design's, noted are the disadvantages of these features.

Natural Draft Design
1) colder burn resulting in the incomplete burn of the fuel, creating more smoke, more creosote. 2) Usually has a 35% larger water jacket then forced draft units of the same output rating.
3) The larger water jacket means there will be a higher cost for heat transfer fluid.
4) Longer chimney required to generate combustion because of natural draft design.
5) Ash pan required due to higher ash and charcoal content due to incompletely burned fuel.
*If you see a smoking outdoor boiler there is a 60% chance that it is of natural draft design!*
The other 40% are likely caused by improper use and poor burning practices be used!

Forced Draft Design
A forced draft fan creates a controlled hot fire, that burns the smoke & gasses created in the combustion process. This is an option on some natural draft brands, but putting a fan on a boiler not designed for forced draft does not mean you will get a hot clean burn!

Legs to raise boiler for ease of loading - optional on some brands.

An external rear chimney means the chimney flue runs colder as it is exposed to the cold creating a situation for more creosote build up, not included standard on most brands using this system.

A square fire box and water jacket means more hydronic dead spots (colder water areas because of lack of water flow, also creates a place for sediments to come to rest in the corners) and more welds creating the potential for more corrosion problems.

Water baffles (ripple top) instead of heat exchanger tubes, means more welds and creates a place for sediments to come to rest, creating the potential for more corrosion problems.

Loading doors with out safety catches.

Ash pan & grates result in unburned product as when coals fall through grate the are below the combustion air and go out. The Wood Doctor Certified Boiler Plate Series has no ash pan as the fuel stays up in front of the forced draft combustion air fan until it is burnt, leaving very little ash.

Most all boilers that have an ash pan are modified boilers of original natural draft design.

Wood & coal boilers incorporate an ash pan, primarily because it is required due to the amount of ash you will have from burning coal (approximately 18 gallons of ash / ton of coal).

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Last modified: 06/04/16