I’ve read all the hydronic related postings I could find on your site but I didn’t find anything specific to my needs.
I live off the grid in Alaska and am fortunate to live in an area where I have access to all the bituminous coal I need for free. I’m wanting to use a hand stoked coal boiler in my garage to heat the garage and the rest of the house (approx 2200 sq ft everything included). I understand the concept behind a closed loop system and its components but I am curious if you think there is any merit to an open loop system.
My thought is a coal boiler with a large capacity (50-100 gal or larger tank) that is vented to atmosphere. The idea being that in the event of my electrical system going down and the circ pump not running or zone valves opening, the boiler (having a burn time of 12-18 hours) would simply relieve excessive heat and pressure by venting to atmosphere (outside) and in effect slowly boiling off the water or antifreeze but not so much that it goes dry and results in a catestrophic meltdown. I would still include a PRV just incase something obstructs the open air vent. Ultimately I just don’t want to rely on the pumps and cold water make up to save me from a meltdown.
Am I on to something or is this crazy and I just don’t know it?
Thank you for your time, you do a great job with your column!
You’re not crazy and there are many out there heating with coal. I worked for many years in West Virginia and Kentucky, and in the more rural mountain areas you could find coal almost anywhere. Kids could pick up all their parents needed to heat a house just by walking along the railroad tracks as the hundreds of over-flowing coal cars that passed by each day lost those pieces piled too high. People tend to heat with the fuel that is the most plentiful in their immediate area.
There is no question that a closed loop hot water boiler system under pressure will require more safety devices to prevent a high pressure blow-out, but there are thousands and thousands of these systems all over the world that have worked perfectly for many years using many different fuels. If loss of power is a concern, it would be easy to add a battery backup supply since the circulating pump and any motorized zone valves will require very little power to keep running. Some system manufacturers offer an optional DC pump that is piped right next to the AC pump, and can be quickly valved over if the AC pump fails or looses power.
All pressurized hydronic heating loops and boilers have more than one pressure relief device and in most cases a power failure during a roaring fire just means the boiler will start converting some of the water in the boiler to steam which gets vented out one of the relief valves. As soon as this starts, the auto-fill valve will sense the loss of water and let in more makeup water which will cool down the process for a few minutes. This cycle will repeat several times until you can bank the fire down or the power comes back on.
I agree that an open pressure hot water boiler might be easier to maintain and there are many now being made as a complete package. They look like a small outhouse, and all you need is a supply and return line from the unit to the hydronic heating system in your nearby house. Unfortunately, your problem will not be which type unit to buy – open or closed loop. Your problem is coal burns much hotter than wood and has more smoke issues than wood. Many wood fired boilers do not have cast iron grates or fire-box liners which are better at containing the hotter coal fire. Also, unlike wood smoke, coal contains different amounts of sulfur, depending on the seam of coal being mined, and if you have never caught a whiff of the smoke off a nearby coal fire you don’t know what I am talking about.
This means you will need to make sure the alternative fuel boiler you select is either designed to burn coal, or has optional equipment to allow it to burn coal. However, if you are in a very cold area and coal is free, then I believe it will be worth the effort for you to make this happen. Let us know how it worked out.