EFM Summer Settings for Domestic Hot Water

Thought it would be interesting to see what everyone is using for domestic water settings and learn from others on how to most efficiently operate in the summer.

We are running successfully with our EFM, but looking to reduce the 5 dump calls per day as they waste 97 cents of extra coal per day. Yes, it is still much cheaper than oil, but we frugal here in Vermont!

The following are our settings and other possible relevant information on our system;
3 teeth
2-3/4 air
200 f HL
130 f LL
10 deg dif
Honeywell L7224 aquastat
Honeywell 6006a outfire aquastat
Honeywell High auger temperature sensor
Logo programmable relay with
90 minute outfire time, 5 minute stoker time
100 minute dump time, 20 minute call time, pulling in a zone of 5 ft of copper finned radiation in a bathroom, of which it takes 6 minutes before stoker starts, and 10 minutes of stoker operating until the stoker shuts off on high limit. Daily average 5 calls per day.
Display of outfire time accumulation, outfire call counter, dump time accumulation, dump call counter, stoker hours and time since last ash removal (via fines dump lever)

Chart recorder recording bottom of burn pot temperature, boiler water temperature, breech stack temperature and dump zone pipe temperature

35 ft masonary chimney with .005" to .01" draft on breech on a 85 deg day after stoker has been off for over an hour.
Aluminum foil over barometric damper
Fully insulated and jacketed boiler and base with all seams and gaskets well sealed.
Full auger length with boiler puttied coupling
2,250 lbs of rice coal above the auger box in a bulk bag removable skid.
Oil boiler completely disconnected.
5 people domestic water needs.
Tankless coil in boiler never hooked up as we have a Superstore water indirect heated 60 gal water tank.

EFM's using a tankless coil run differently in the summer than one with a separate superstore. I believe the Honeywell L7224 aquastat will run towards the low limit setting with a tankless coil, as it is just water temperature pulling in the stoker. In a system with a superstore, it runs towards the high limit setting.

In our system, the superstore appears to the aquastat as any other heat zone would. When the zone valve turns the circulator on, the boiler gets ready for a big heat load and turns the stoker on. Since the stoker at 3 teeth is putting out more btu's than needed and it takes a while for the circulator to reheat the superstore, the boiler overruns the call in btu's and the stoker shuts off on the high limit.

While all this is fine and the domestic hot water needs are satisfied, the result is the boiler temperature is near or above the high limit setting most of the time. This leaves little room for the outfire (hold fire fluff) timer to run the stoker.

This may not be the case for people with a tankless coil, running at the low end of boiler temperature.

While my wife wants me to dump the heat in our swimming pool (I think Rob does that),I have some ideas on how to reduce or eliminate the dump calls using our Logo programmable relay and an additional 6006a aquastat.

The plan would be to wire an additional 6006a aquastat to the input of the Logo, set it at 170(?), then when a natural call for heat occurs, the Logo would let the stoker come on with the L7224 for 5 minutes, then after which it would only let the stoker come on if the temperature was below the 6006a aquastat setting. This would hopefully end up leaving temperature lower when the call for heat was finished. This would leave btu room for the outfire timer later to come on without going over the high limit.

The Logo would bypass the 6006a setting during outfire calls.

As the Logo will only be breaking the stoker wiring from the L7224 controller, the safety high temp lockout will still work from the L7224.

Perhaps there is an easier way than the above, or perhaps I should just quit messing with an already working non-broke system!

Still be interesting to see what others are using. I seem to remember one guy running at a teeth (tooth?) setting of 1!








Posts: 134
Joined: Wed Oct 22, 2008 8:27 pm
Stove/Furnace Make: EFM
Stove/Furnace Model: 520
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I'm sort of confused I don't understand why you have the stoker coming on if you are trying to lower your boiler temp. Isn't the point to get the excess heat out of the boiler and run the temp down to the low limit? I don't run one so I'm not really sure how they go

I would use an outdoor reset module with your L7224 and keep the boiler temp lower. You will still have your high/low limits but will keep the boiler temp from overshooting. Do you run your superstore at 120 degrees or do you go hotter and use a mixing valve?

Scottscoaled wrote:I'm sort of confused I don't understand why you have the stoker coming on if you are trying to lower your boiler temp. Isn't the point to get the excess heat out of the boiler and run the temp down to the low limit? I don't run one so I'm not really sure how they go

Scott is a wiring pro and I'm not, but I would ask the same question. If the low limit is set high enough to provide reasonable boiler water temp, why don't you let the aquastat decide whether the draw of boiler water by the indirect requires that the stoker run?

Two additional notes:

- If the indirect is making the boiler run hot and necessitating frequent use of a dump zone, it must be clobbering whatever the efficiency rationale is for the indirect.

- I've run with a coil and with an indirect, and to me there is no comparison. I would skip the indirect and run off the coil. A coal boiler has to stay hot anyways, and to me the indirect is just a middleman that ultimately slows the production of DHW relative to a coil.

Mike

My first impression is that he is trying to prevent outfires. I'll have to mull over this in my subconscious for awhile. Yes, my bro-in-laws family runs at 1 tooth.

We need the dump to fluff the fire to prevent outfires. As both the outfire timer and dump timer reset to 0 time every time the stoker comes on, the dump coming on at 100 minutes means the outfire did not fluff the fire due to high boiler temperature.

The outdoor reset is an interesting question. I don't know how they work. Would it result in more "running room" for the outfire timer?

vermontday wrote:Thought it would be interesting to see what everyone is using for domestic water settings and learn from others on how to most efficiently operate in the summer.

I run 4 teeth, a touch over 4 for air (rice coal), and 1.5 minutes every half hour on the timer. 140 LL and 185 HL. I have used 3 teeth before, but for simplicity I just left the feed alone this year.

vermontday wrote:While my wife wants me to dump the heat in our swimming pool (I think Rob does that)

I have no dump zone, and have never found the need for one. I allow gravity circulation between the EFM and my oil boiler, so the extra thermal mass helps keep things at a steady temperature. All piping and both boilers are insulated, and usually stay around 160-170 F. I use a well-insulated 80 gallon indirect for DHW, and I enjoy the steady output of 120 F water.

vermontday wrote:EFM's using a tankless coil run differently in the summer than one with a separate superstore. I believe the Honeywell L7224 aquastat will run towards the low limit setting with a tankless coil, as it is just water temperature pulling in the stoker. In a system with a superstore, it runs towards the high limit setting.

In our system, the superstore appears to the aquastat as any other heat zone would. When the zone valve turns the circulator on, the boiler gets ready for a big heat load and turns the stoker on. Since the stoker at 3 teeth is putting out more btu's than needed and it takes a while for the circulator to reheat the superstore, the boiler overruns the call in btu's and the stoker shuts off on the high limit.

While all this is fine and the domestic hot water needs are satisfied, the result is the boiler temperature is near or above the high limit setting most of the time. This leaves little room for the outfire (hold fire fluff) timer to run the stoker.

My system is wired the same way you just described, and I have no issues with overheating.

Are you running a circulator off C1/C2 in the L7224 aquastat? If not, just disconnect the end switch from the TT terminals and let the stoker fire off the low limit. If you are driving a circulator off C1/C2, move it to a relay independent of the L7224...then the unit will behave like it has a tankless and only fire when the low limit is reached.

Also - That Superstor should "hold back" the EFM with only 3 teeth of feed. As per the manual, the Superstor needs to be piped with 1" pipe, 1" full port zone valve (if used), and it needs 10 GPM of flow through the coil. The manual says the coil alone creates 8 feet of pump head, so it is possible that the coil inside the indirect may be underpowered and not transferring heat from the boiler properly. Another possibility is calcium deposits on the coil from hard water...that will result in a small difference in temperature between the boiler supply & return pipes on the indirect.

vermontday wrote:The plan would be to wire an additional 6006a aquastat to the input of the Logo, set it at 170(?), then when a natural call for heat occurs, the Logo would let the stoker come on with the L7224 for 5 minutes, then after which it would only let the stoker come on if the temperature was below the 6006a aquastat setting. This would hopefully end up leaving temperature lower when the call for heat was finished. This would leave btu room for the outfire timer later to come on without going over the high limit.

I think it would be a lot simpler to disconnect the end switch going to the L7224, but maybe that's just me. Don't over complicate a simple problem with additional controls...KISS.

Those are great questions Rob. I will check them out tonight.

I agree I would rather keep it simple.

I will add that my dad uses the tankless coil in his 520 Highboy. He runs it at 4 teeth, 4 air, 160 LL 180 HL, 2 minutes every half hour...he uses the same settings year-round, and the boiler usually stays right at 160 degrees. Neither of us have ever had an outfire.

Pacowy wrote:I've run with a coil and with an indirect, and to me there is no comparison. I would skip the indirect and run off the coil. A coal boiler has to stay hot anyways, and to me the indirect is just a middleman that ultimately slows the production of DHW relative to a coil.

An indirect is a great way to satisify high DHW demand without a larger boiler...it is basically a storage tank with its own coil. If you were comparing the performance of the tankless in your EFM 900 (big btu capacity & thermal reserve) to an indirect with less than ideal piping, it is easy to see that the 900 w/ tankless would have the edge. Someone with an EFM 350 and a 80 gallon whirlpool tub might not have the same experience. The bigger boilers do much better with a tankless coil - If I had an EFM 900, I would be using just the tankless coil.

Rob R. wrote:I will add that my dad uses the tankless coil in his 520 Highboy. He runs it at 4 teeth, 4 air, 160 LL 180 HL, 2 minutes every half hour...he uses the same settings year-round, and the boiler usually stays right at 160 degrees. Neither of us have ever had an outfire.

Pacowy wrote:I've run with a coil and with an indirect, and to me there is no comparison. I would skip the indirect and run off the coil. A coal boiler has to stay hot anyways, and to me the indirect is just a middleman that ultimately slows the production of DHW relative to a coil.

An indirect is a great way to satisify high DHW demand without a larger boiler...it is basically a storage tank with its own coil. If you were comparing the performance of the tankless in your EFM 900 (big btu capacity & thermal reserve) to an indirect with less than ideal piping, it is easy to see that the 900 w/ tankless would have the edge. Someone with an EFM 350 and a 80 gallon whirlpool tub might not have the same experience. The bigger boilers do much better with a tankless coil - If I had an EFM 900, I would be using just the tankless coil.

I figured I'd hear from Rob on this.

Yes, the 900 is bigger, but a 520 is a formidable DHW machine in its own right. Even at 4 teeth, that should be enough coal to sustain production of somewhere around 2.5 gpm on top of the thermal reserve provided by 40 gallons of hot boiler water. I would agree that if you have a special need, like the Mrs. wants to fill a huge soaking tub at 5 gpm, it's probably worth having the indirect to maintain domestic tranquility. However, for people who are worried about DHW consumption by teenagers and long showers, I think the boiler can put btu's into the coil faster than the btu's can be transferred via the indirect. For that type of situation, I think the indirect could be at a disadvantage relative to a coil.

In my case, the "less than ideal piping" is that I can't use a coil in this boiler, so I pretty much have to use an indirect. My situation is made worse by factors that don't arise in most situations - boiler design and controls, limited ability to circulate boiler water, big DHW lines/recirculation issues, etc. - but I do think an indirect can introduce constraints relative to a coil that should be considered.

Mike

I hope you meant 2.5 GPM not GPH. I've heard of a loooog hot shower, but that would be chilly at some point. I run 135/150 all summer and a 40 gallon indirect. I thought of spending 35,000 for a solar array...AND a Geo Thermal setup for 50K.....thought about it for about 1/1,000,000 of a second ...and determined that was just plain stupid. The short payback would be tough to take......49 years, hmmmmmmm, where are all the pointy-heads when you ask that question!

Thanks for catching that.

I guess payback is really my concern about the indirect. If the savings from running the boiler cooler justify the cost of the indirect, that's fine. However, I think people sometimes sell short the ability of a coil to meet DHW needs, and that an indirect is not always needed or even helpful.

Mike

Pacowy wrote:I figured I'd hear from Rob on this.

Yes, the 900 is bigger, but a 520 is a formidable DHW machine in its own right. Even at 4 teeth, that should be enough coal to sustain production of somewhere around 2.5 gpm on top of the thermal reserve provided by 40 gallons of hot boiler water. I would agree that if you have a special need, like the Mrs. wants to fill a huge soaking tub at 5 gpm, it's probably worth having the indirect to maintain domestic tranquility. However, for people who are worried about DHW consumption by teenagers and long showers, I think the boiler can put btu's into the coil faster than the btu's can be transferred via the indirect.

You knew it was only a matter of time.

As you pointed out, there is a big difference between a long & steady DHW draw and a shock load.

The issue I had with my 520 and the coil was when the boiler got hit with a big DHW load after an afternoon running on the timer. The first 5-10 minutes of stoking after an afternoon on the timer doesn't create a lot of fire, and it was possible to exhaust the thermal reserve of the boiler before the stoker could catch up. You didn't have to fill the tub at a firehose rate to do it, just letting the washing machine fill and getting in the shower was enough. Running the boiler at a higher temperature and 5-6 teeth took care of that issue, but at the price of increased coal consumption and a warmer basement.

It is all a balancing act...needs vs wants, and of course cost. In my case, it was about $600 more for the 80 gallon indirect than a 7 gpm coil, gasket, and mixing valve. I need to save about 7 lbs per coal per DHW day (DHW only, I figured 120 days per year) to break even on the additional cost of the indirect in 5 years. If my cost of coal goes up, the breakeven is shorter.

Having two AA 260's running 24/7-365 in a ten apartment complex, I can tell you tank-less coils will provide plenty of domestic hot water, HOWEVER the demand, once satisfied, makes it impossible for a boiler to 'ramp down' quickly enough to prevent overshoot....and overheating. Doesn't matter who's boiler it is.....so, a dump zone......or use of a big indirect and some tankage sure helps out. My 520's and 900 were set at 4 clicks, 4.5 air burning buck. AHS, AA, Keystoker and now LL work just fine without major adjustment.

Remember, this is a perfect time of the year to shut it down, clean stack piping, replace as necessary and vacuum out the boiler and passages.

We never had problems with the 520 at 4/4 in the hot summer at efm. I would run the timer at 2 minutes and disconnect the other stuff for the summer.