dump zone

I am nearly complete installing my efm 520, getting pretty excited. My neighbor who has a harmon unit in his house has been helping me along. He insists that I need to have a dump zone, a place to loose heat on these days that are not really cold but still too cold for no heat. I do not recall reading of anything like that on here. Does anybody do such a thing.

I have long runs into house from furnance. I have appx 100' into house and another 50 to the furthest exchanger. Because of this I have water circulating in my loop nonstop to avoid cold water sitting in 150 of pipe.I figure I would loose some heat.

I'm still a rookie, but any solid fuel boiler will need a dump zone, which is essentially a seperate high limit aquastat wired to your burner control and your circulator pump.

Because the fire doesn't go 'out' like with gas or oil, when the call for heat ends, the boiler will continue to build heat. The high limit aquastat will kick off your burner control and turn on the circulator to 'dump' the excess heat out of the boiler. It's more common for the dump zone to operate in warmer weather, because the boiler isn't calling for as much heat as it is when it's colder, so it is idling more of the time (and setting that idle is damn tricky..... ).

That said, if you are constantly circulating water, it would 'appear' to be a non-issue. However, you're boiler probably came with a high limit 'dump zone' aquastat, and it's much much better to be safe and have it set then it is to have your boiler overheat at some point down the road.

I sure others can give you more details, but that's the little I know at the moment.

Eight year installation. I don't have a dump zone. Never needed one. I circulate water constantly from the coal boiler to the oil boiler. Your mileage may vary.

mooseman100 wrote:I am nearly complete installing my efm 520, getting pretty excited.

You can continue getting excited. You have one of the finest stoker boilers made, and it normally doesn't require a dump zone. You can add an aquastat for that purpose if you wish, but I have never had an issue with high temperatures with my 520 (my dad doesn't either). An EFM 520 boiler holds about 40 gallons of water (Highboy is about 54), and weighs 750-800 lbs. That is a lot of mass, and as long as you have the controls set properly, it should maintain a stable temperature just fine. One of the nice features of the EFM stoker is that it doesn't require 15 minute timer cycles to keep the fire alive. 1-2 minutes of run time every half hour is usually sufficient; especially if you have a strong chimney.

When set at 5 teeth of feed, my 520 will only "coast" about 10 degrees after a heat call...less if the stoker was only running for 10-15 minutes. When set at 160/200 and 1minute every half hour on the timer it usually hangs out at 160-170 degrees.

kstills wrote:However, you're boiler probably came with a high limit 'dump zone' aquastat, and it's much much better to be safe and have it set then it is to have your boiler overheat at some point down the road.

You can order a brand new DF520, and it won't come with a separate aquastat for a dump zone. The high limit function of the triple aquastat will prevent the stoker from running above that setting. If someone is concerned about the aquastat malfunctioning, it is easy enough to add a second control to disable the stoker above a preset temperature. I had an extra L4006A kicking around, so it is installed on my 520 and set at 220 degrees. 10 tons later it has never approached that temperature.

A "dump zone" can be as simple as a switch (aquastat) that circulates your normal load if (and/or maybe when) you have an over temp

Sting wrote:A "dump zone" can be as simple as a switch (aquastat) that circulates your normal load if (and/or maybe when) you have an over temp

That's the way to do it, but why bother? All solid fuel boilers overshoot somewhat and their design is to store energy. Run the thing for a while before you bother spending time and money for something you more than likely have no need for.

You don't need a dump zone if you properly size your expansion tank. The wood boiler guys need one because they run unpressurized piping systems. With closed pressurized boiler when the boiler overheats, the water expands. If you size your expansion tank properly this expanded water goes in it. Your boiler stays hot, ready to serve the next heating demand. To repeat you DO NOT need a dump zone. It's desirable not to have one.

I have created some graphs of the design guidelines but do not have them in a form for posting. Basically you oversize your expansion tank by the amount of expanded water volume in your boiler. Select the high temperature to whatever you want, 250, 270 etc. Just so the resulting pressure increase doesn't reach the safety valve release pressure. All will be safe and boiler water will return to the normal range when radiation circulation occurs. It's a straight forward design procedures explained in Siegenthaler's book, Modern Hydronic Heating.