EFM 520

I think I have finally made up my mind on a EFM 520 boiler, I have weighed the pros and cons of each system in my head 100's of times, and I think the EFM is worth the extra money over a Keystoker or Alaska furnace. I'll be hooking it to a heat exchanger that will go in the plenum that is above my existing furnace, that way I can keep the same blower setup with 4 cold air returns and all the hot air register, the distribution system was engineered pretty good so I don't want to change it. I like the idea of not having to fill a hopper. The guy that I'm getting it from has 2 kinds, a newer style plate boiler and an older tube boiler, I'm not really sure what the difference is or why one is more expensive than another one, they both have the same BTU's and efficiency I think?

e.alleg wrote:I like the idea of not having to fill a hopper.

You still need a hopper of some sort. Most people get a 55 gallon drum and put it right in the bin. Cut a hole about foot around in the bottom and place it over the auger on cinder blocks. That will allow you to get about 450lbs.+ on the worm that is useable.

Look at it this way, wherever the worm is without a hopper you can draw a cone from its center at a 45 degree angle. That's all dead space as far as the coal going on the worm.

Tube boilers are the old style, plate boilers are the new kind. buy one with the square door not the little round door, it is easier to clean and you can fit ur baffle plates through them. if u want i have pictures of my 520 dual fuel on page 11 of pictures of your stove in the forum. if you have any questions you can pm me.

Mino, How well does the oil burner work on your 520?

My oil burner is dodgey and it would be nice to have a built-in backup in my house, since it's chimney limited.

I would not expect it to be more efficient than a straight oil burner.

I only use oil for the summer or if i go on vacation. for domestic hot water it works fine, but if you try heating with it it never shuts off. it fires at 1.5 gallon an hour, so do the math. i use coal 99.9 percent of the time and it holds a fire pretty good in the summer months even when it is humid too, well put it this way last week the power was out for about 6to 7 hours when the power came back on the stoker held the fire and started chugging away.

If your oil boiler was sized for heating your entire home and now is only used for back up and summer heating you should change the firing rate of the oil burner. 1.5 gallons/hr. could be cut back to under 1.0 gallons/hr. This will make you oil boiler much more efficient because it will be firing longer rather than short cycling. It will however reduce the Btu output. Since you only use it for summer hot water or times you are away the reduced output would not matter.

Continuously? That's odd. You'd think you you easily put a controller on it.

Is that the 'book gph' figure? My oil burner is rated at 1.25gph or so; since it doesn't burn continuously, it does about 1/4 that per hour.

no, it shuts off , when its up to temp(oil that is) but with a heavy load in winter months it takes a while to reach temp. the boiler is designed for coal with oil back-up.

If it's cycling, then your consumption shouldn't be toooo bad.

If it were burning 1.5 gph continuously, you'd go through 36 gal a day and rip through a 275 tank in less than 8 days. :shocked!:

My old W-M oil boiler is rated at ~1.25gph (book), and along with the oil water heater, they take about 30 days to drain the 275 on the coldest months.

So, together they average about .4 gph over that month. I'll guesstimate that the water heater is about 25% of that consumption, so the boiler is probably taking a little under .3gph. That works out to the oil boiler burning about 14 mins an hour, average, during the worst months. (Yanche, correct me if my logic is wrong.) Hearing that G@#$*#@ thing go for 1min every 4 sounds about right.

In my old house my oil burner used to cycle like that on/off/on/off and my brother was over one day and fixed it by adjusting something inside the thermostat. I don't know what it was but it fixed the problem with no parts or money. after it was fixed it would run for 10 minutes and then stay off for 40 minutes or so.

Any oil burner boiler or furnace operates most efficiently when it is operating near it maximum design output. Hopefully the manufacture has matched the firing rate of the burner (gal. per hour) with the heat exchangers capability to get the heat into the boiler water or furnace air plenum. But most of the time the appliance is not operating at full capacity. The coldest day of the year is rare event. So properly sized equipment is chosen to meet most of the coldest days. This means it will not heat your house on the coldest day of the century. But it will heat your house on the average coldest day. This is the most efficient operating design point. Now lots of times you don't need full output, so the only thing you can do is cycle on and off the burner. It gives a blast of hot combustion gases then none. The on-off is controlled by the both the thermostat setting and the boiler water or furnace plenum temperature. The boiler water or air plenum averages out the heat distributed to your house. Room thermostats especially older models have a little tiny heater in them, called a heat anticipator. It's purpose is the trick the switching element in the thermostat to shut off sooner. It's adjustable. You need it because the room warms up slowly and then overshoots the set temperature. The heat anticipator provides a little extra heat when the thermostat is calling for heat. Set it correctly and it works fine. If it provides to much heat the boiler/furnace will short cycle. Constantly on/off.

My earlier comment on reducing the nozzle firing rate on a oil boiler used for both summer domestic hot water production and winter back up heat was based on the same idea. No need for a large 1.5 gal/hr. nozzle when all you are doing is heating domestic hot water. Switch to a smaller size and run the boiler more efficiently. But since you have reduced the maximum heat production capability you cannot now heat your home on the coldest of days with oil. It's all a balance of what you want. If all you want is not to return to a frozen home that is normally heated by coal, but while you were gone the fire when out, you can get by with a much smaller firing rate. Some oil service companies will tell you then can make your existing oil furnace more efficient especially if you burn our special supper dooper oil. What they do is reduce the nozzle size. Sure it burns less oil and you like that but if it gets really really cold so will your house be really really cold. Then they get to service it and put the larger nozzle back in. There is no free lunch!

So, do the auxilary oil burners work ok, or are they too inefficient for vacation or the corners of the coal season?

Yanche, I know that you did not think much of them. I'd like to save a stack, if I can.

I would think that even if the oil burner is ineffecient, it will keep the house warm for vacations and if you have coal burning issues. Even a very ineffecient form of heat is good as a backup system. A few days of oil burning is much better than frozen pipes and a flooded house.

I keep my propane system operational for the same reasons. I hate using the expensive stuff, but it does keep the house above freezing.

Greg L.

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Charlie Z wrote:So, do the auxilary oil burners work ok, or are they too inefficient for vacation or the corners of the coal season?

Yanche, I know that you did not think much of them. I'd like to save a stack, if I can.

I guess I didn't make my point about efficiency very well. Let's try again. All but the most modern oil fired boiler have a combustion efficiency around 84%. That means 84% of the approximately 140,000 Btu in a gallon of #2 fuel oil gets converted to heat. You also have equipment efficiency, how well the appliance converts that hot flame to hot water. When the boiler is operating at the max firing rate the flame to water heat exchanger is doing the best it can. It's at the max design point. All the little tits on the casting are collecting the flame heat and transferring it to the boiler water. The manufacture rates the boiler at a certain Btu and sets the corresponding nozzle size. If you reduce the nozzle size the boiler operating efficiency will go up. The heat exchanger stayed the same but it now works better. More tits on the casting than are really needed to get the job done. Combustion efficiency stays the same 84%. Can't change that it's largely just combustion physics/chemistry. So if you have an oil burner sized for heating your house AND you made no changes AND the oil burner is now used only to heat hot water in the summer because you now heat with coal, it's to large. It will operate inefficiently, short cycle, etc. Combustion efficiency (84%) stays the same operating efficiency goes down. If I now change the nozzle to a smaller size operating efficiency will now go up. The boiler water Btu production is more closely matched to domestic how water needs. BUT in winter, if your coal fire goes out you want some backup oil heat. It will work with the same 84% combustion efficiency and a better than manufactures rated operating efficient. BUT, you can't get the original Btu's out of it because you reduced the firing rate. If all you want in winter is to keep the house from freezing it will work. If you want your cake and eat it too, change the oil burner nozzle seasonally. Small size in summer, standard larger size in winter.

Charlie Z. Want to save a chimney stack put the oil burner on a direct vent system. Use the clay lined chimney for coal.

I should have been clearer, too. I get the matching the nozzle to the need, etc.

The question is, how does the AFUE (output efficiency) of the combo coal boilers compare to a modern, dedicated oil burner?