350 EFM Coal Stoker Info

Let me give you guys a little info on the 350 EFM . First of all every EFM mfg with a round fire door is not a 520. I am fairly new to the forum but I have been working on coal stokers for about 30 years & I was surprised how many people didnt know about a 350 EFM boiler. Around 1960-61 EFM made a 350 boiler which was round in the front. Hard to tell until the covers are off. To the best of my knowledge these were only made a few years & put out about 90,000 btu. I have one of these in the shop. After that they manufactured another 350 which was a rectangular boiler but the boilers were mfg by General Machine Co. and others were mfg by Loline Co. These were mfg from around the early 60's to the late 60's. The rating on the later one was 112,000 gross btu. Many of these boilers were passed off over the years as a 520 & many people have them today & still think they have a 520. Years ago many plumbers installed 520 pots in the 350 to increase the BTU rating on thers boilers. The 520 pot is about an inch larger in diamater than the early 350 pots. Looking at a 350 with the jacket on it is hard to tell the difference between them since the jackets are the same on the rectangular 350 as the 520. A rectangular 350 measures 23" wide 26" high & 30" long. A 520 measures 25" wide 27" high & 34 1/2" long. I have seen many of these 350s heating 1500 to 2000 sq.ft. with 2 circs. with no problem. I hope this helps some of you guys out there that were inquiring or didnt know about these boilers. I even had a guy drive 50 miles to see one of these because he didn't believe me but they say seeing is believing.

Welcome to the Forum scrapper, always nice to meet a person who rebuilds the oldies but goodies!

Also thanks for the information, it's interesting to see the story of how these old tried an true units evolved through time.

See the response under the 520 highboy thread.

Doesn't the 350 have a 6" exhaust as opposed to the 8" on the 520's? And it exhaust in tthe middle of the top backside instead of the bottom? That would make it an easier install in alot of houses. Yes, welcome to the forum, hope to see you soon Scott

Scott. The exhaust on the 350 is the same as the 520 .same heigt same location &it is is also 8inches in diamater.read info posted about the350.

My mistake. I think I was looking at an oil boiler Sorry. Scott

350 EFM Coal Stoker Still the best size unit ever made by EFM for a modern house. 90,000 BTU is more than most people need especially if zoned.

EnergyManager wrote:350 EFM Coal Stoker Still the best size unit ever made by EFM for a modern house. 90,000 BTU is more than most people need especially if zoned.

A 350 produces alot more then 90k BTU even the orignal ones with the small pot & S-15 stoker had a max of 6 teeth feed rate 2.5lbs per hr per tooth with rice coal 15 lb max feed rate per hr 15 lbs x 13.500 BTU per lb = 202.500 BTU's subtract
15% or 20% for heat loss depending on set up 172.125 BTU's to 162.000 but's max out put . Now stick a S-20 stoker & pot
your at the 520 #s max feed 8 teeth 20 lbs per hr max with Rice coal with buck it is 16 lbs per hr max feed .
20 lbs per hr x 13.500 BTU per lb = 270.000 BTU's subtract 15 to 20% for heat loss 229.500 BTU's max to 216.000 BTU's

Remember these # are for the older 520 -s-20 which olny had a 8 teeth feed rate max The newer s-20 with the longer gear arm and with the bigger pot has a feed rate max of ten teeth 2.5 lbs per hr 25lbs per hr max rate . 337.500 BTU's subtract 15 to 20 % heat loss 286.875 BTU's to 270.000 BTU's max out put using coal at 13.500 BTU per lb the numbers will be higher or lower depending on the coal being used. Even at 4 teeth with a 350 the out put would 108.000 BTU to 114.745 BTU's

3 teeth feed rate is from 86.625 BTU's to 81.000 BTU's . Agreed the 350 is capable for most of the newer homes aswell as alot of the older ones being that is what has been heating them more often then 520's most people think they have a 520 when it ends up being a 350 in the basement that's been heating the house for decades.

a 350 would be nice, I don't really need a 520... but the 350s are hard to find.

but the 350s are hard to find.

Here's one:

EFM 350

So could you block off some of the grate area and back off the feed rate to get to 6#/Hr and run it hard and efficiently at that heat rate?

Teddy wrote:So could you block off some of the grate area and back off the feed rate to get to 6#/Hr and run it hard and efficiently at that heat rate?

No, this is an under fed stoker. It looks like a pot and the coal is driven by an auger up through the pot. If you block anything off, the stoker won't work. If you back off the feed rate, the fire will migrate down in the pot. This can do damage to the grates.

MAN, this is an old thread! Interesting though, a 350 should a a real good unit. Pacowy has one for sale;
**Broken Link(s) Removed**
Not a bad price for a refurbed EFM.

-Don

Thanks Don. By block off I simply meant to plug up some of the air holes so that it is incapable of burning above a certain lower burn rate because it can't get the air. So what would be the minimum fire rate for this pot? It's designed for 15#/hr. Would it still work well at lets say 6#/hr? Teddy

Teddy wrote:Thanks Don. By block off I simply meant to plug up some of the air holes so that it is incapable of burning above a certain lower burn rate because it can't get the air. So what would be the minimum fire rate for this pot? It's designed for 15#/hr. Would it still work well at lets say 6#/hr? Teddy

I don't know what the burn rate of a 350 is. From what I understand the later 350 that Scrapper mentioned is the same stoker as a 520, with one difference, the ash ring. The 520 has a 14.5" ash ring and the 350 has a 13.5" ash ring. This smaller ash ring decreases the BTU output of the 350.

Pot stokers are complicated, you can't just start blocking things off and expect it to work.

-Don

AFAIK the recommended minimum firing rate is "4 teeth", which corresponds to 10 lb/hr of anthracite rice. Due to the small ID of the auger tube, stoker bit will not feed well in this or in a 520.

Again, to me this raises the question of the basis for the 6 lb/hr spec. Even when coal was widely used, the minimum firing rate of the smallest residential stoker offered by EFM was 10 lb/hr, and the recommended firing rates of the two smallest residential stokers were 15 lb/hr (350) and 20 lb/hr (520). It seems like either the 6 lb/hr reflects a small space with a minimal heating load and no significant DHW requirements, or it has been developed on a basis that differs from normal stoker sizing standards.

Mike