Scottscoaled boiler sizing method

In response to all the threads about boiler sizing and not keeping warm.


Scott's two step boiler sizing method;

Step 1. Determine if the building is less than 5000 square feet, has four walls and a roof.
Step 2. Install EFM 520.

I too have noticed a lot of threads popping up about people disappointed in the output of their boiler. In some cases I think the boiler was sized too tight to the load, and in other cases the combustion fan can not overcome the resistance of undersized coal and achieve a proper burn...in other cases the inclined bed stokers tendency to plug with clinkers caused problems.

It is always prudent to do your research...but generally speaking I think an EFM 520 is the most versatile stoker boiler you can put in an average home. It will happily run at a wide range of output levels. The ability to burn rice or buck, and have the blower capacity to properly burn undersized coal at moderate feed rates makes it a winner.

Blah, blah, blah........


Rick's sure fire method:


Install AA 260.


If you need a dump zone for overfiring............put in a pool




Rick

Not sure what Rick is blah-bering about here.

Everyone's loyalty to their favorite equipment is admirable, but to me the key to happiness with coal-fired central heating is to make sure it satisfies WTRR standards. This not only covers traditional heat-loss and other load measurements, but also provides enough extra capacity to heat the building "With The Roof Removed".

Mike

I agree, an oversized coal appliance is better, I believe for a couple reasons...
#1 - No problem keeping warm
#2 - I think a coal appliance that can meet its heat demand at only 60-70% its heating capacity will do so more efficiently than a smaller appliance running at 95% its capacity. Seems that the harder you push a solid fuel burner, the higher percentage of BTUs produced will go out the chimney. But thats just based on my own observations...........

I have an architect friend that once told me that it was really easy and simple to design a structure that was way over-built, but quite another to build a building that was economical, just met the load requirements and was safe.

I think the same principal applies to sizing heating appliances. Anyone can throw a huge wood stove in a home and heat the building, but it is quite another to design an efficient boiler that just meats the heating requirements, but no more, is safe and is economical with a decent return on investment.

Naturally when you have an engineered system, you must have all aspects of the system run in harmony, but get a few things wrong and the unit will not run properly. I have seen everything from undersized boilers, to check valves put in wrong, to unqualified people install heating appliances. We are human and mistakes happen, but overall I have a lot of respect for the technicians who set up a heating system that just meats the requirements, but no more, and I think as society with a diminishing energy supply, it is best if we use logic to heat our homes instead of sheer size. If it is an AA 260 or an EFM 520, so be it, but calculations should be made first.

Guys,

I have only one point of reference to work with, at least with coal burning, but I went with an efm520 and it was plug and play. I haven't made it do anything wrong, and I can screw up in my sleep. I have to agree with Scottscoaled except I think the roof is optional

Waldo

NoSmoke wrote:I think as society with a diminishing energy supply, it is best if we use logic to heat our homes instead of sheer size.

Aren't you the guy with an 800 square foot kitchen at 90+ degrees?

All jokes aside, what prompted this whole discussion was a side-bar conversation between Scott and I. We were discussing the number of posts about people not getting enough heat out of their boilers, and a few phone calls from people in our respective area that were having problems....the one thing that all of the over-stressed boilers had in common was an inclined bed stoker...of various makes and models. I stay in pretty close contact with about 10 people running EFM stoker boilers, 3 of which are running 520's that I installed personally...I have yet to get a PM or phone call from anyone in a cold house.

Call me biased, but I love the fact that a 520 can efficiently run at 50,000 btu's/hr, or 150,000 btu's/hr (and everything inbetween)...the unit is capable of putting out more than 150,000 btu's hr, but at those levels efficiency is not as good and things like the size of the coal and cleanliness of the heat exchanger is much more important.

I think we have people sizing their boiler by the price tag, not by sound judgement.

Lightning wrote:I agree, an oversized coal appliance is better, I believe for a couple reasons...
#1 - No problem keeping warm
#2 - I think a coal appliance that can meet its heat demand at only 60-70% its heating capacity will do so more efficiently than a smaller appliance running at 95% its capacity. Seems that the harder you push a solid fuel burner, the higher percentage of BTUs produced will go out the chimney. But thats just based on my own observations...........

You are absolutly correct. Efficiency is based on input vs available surface area for a given firing rate. More surface area available, more efficient.

NoSmoke wrote:I have an architect friend that once told me that it was really easy and simple to design a structure that was way over-built, but quite another to build a building that was economical, just met the load requirements and was safe.

I think the same principal applies to sizing heating appliances. Anyone can throw a huge wood stove in a home and heat the building, but it is quite another to design an efficient boiler that just meats the heating requirements, but no more, is safe and is economical with a decent return on investment.

Naturally when you have an engineered system, you must have all aspects of the system run in harmony, but get a few things wrong and the unit will not run properly. I have seen everything from undersized boilers, to check valves put in wrong, to unqualified people install heating appliances. We are human and mistakes happen, but overall I have a lot of respect for the technicians who set up a heating system that just meats the requirements, but no more, and I think as society with a diminishing energy supply, it is best if we use logic to heat our homes instead of sheer size. If it is an AA 260 or an EFM 520, so be it, but calculations should be made first.

The problem with applying an engineered solution to coal boiler sizing is that there are too many random variables over which the operator has limited, if any, control. As discussed in other threads, these include variations in coal quality, coal sizing, coal iron content/clinkering, ash buildup, DHW load, fuel/air mixture, severity of actual weather conditions relative to engineering assumptions, etc. If you really sized a boiler to protect against the reasonably foreseeable variations in these factors, it wouldn't bear much resemblance to the one you would pick based on traditional heat loss computations.

Then there is the issue, discussed at length in other threads and mentioned by steamup, that under some circumstances a larger boiler may be more efficient than a smaller one that just meets the load because the larger boiler (generally) has a greater heat exchange area. Yes, there are engineering factors that also work against big boilers, but actual efficiency and performance go beyond following some spreadsheet and installing the size it shows.

I've lived in a few houses with heating systems that originally were powered by coal, and all of the boilers were sized "generously". In the era when coal heat was commonplace, I believe that the people who did boiler sizing had a greater recognition of the significance of the above factors. Coal heat is able to provide enhanced comfort as well as economy, but you won't get that comfort if you "engineer" out the capacity that enables it to be provided. Everyone is certainly free to make their own choices, but I'd suggest studying a little more closely what the Dead Men did before discarding what history has shown.

Mike

Rick 386 wrote:Blah, blah, blah........


Rick's sure fire method:


Install AA 260.


If you need a dump zone for overfiring............put in a pool




Rick

I have to agree, my AA260 does the job very well.
with virtually nothing to adjust it is truely 'plug and play'

As mentioned above, three really is NO one perfect boiler, every heating situation is different.
Many homes are well heated with a small boiler:
LL110
Harman VF3000
Keystoker Kaa2
Then the medium sized homes seem to like
EFM 520's
AA130's
Ka6's
AHS130
Then larger homes and loads are well served by
AA260
Ka8
EFM 700-900
LL220
AHS 260

The the truly large homes or warhouses
use multiple boilers or
some of the monster boilers.

Whatever works,, we always like and promote what we have as 'best'...


Greg L

I think the most accurate heat loss calculation is knowing how much oil was burned, provided realistic efficiency numbers are assigned to each unit.

I would expect a carpet bed stoker to suffer in heat exchange compared to a larger deeper fire pot stoker. Smaller hotter fire often placed in a big box with little provision or not enough for those hot gasses to contact heat exchange surfaces. There is also the pressure to make things compact. In the old time boilers gasses had multiple passes before exiting or in the case of steel fire tube boilers the tubes are horizontal and there are enough of them. Anytime there is a smaller hotter fire the potential is there to better burn or not generate in the first place CO. Air handling has got to be easier with a shallow bed yet too high a velocity can result in not burning initial volatiles. The ideal is one firing rate where required settings can be optimized as is done with other fuels. The need to vary that rate makes a good design that much harder.

Blah, blah, blah. Forget water as a heat transfer method buy AnthraKings pocket the $20,000. Hire a luxury yacht for a week, buy nice jacket and marine fancy cap. Phone up Cindy Crawford and invite her out for the week. Remember money can't buy you love but buys you something so close you will never tell the difference. If in doubt follow Mr Woods story and see what $200MM will buy you. Or, remember that no two heating situations are the same and there are many great options with coal. The only truism here is anthracite rules (OK, bit too).

franco b wrote:I think the most accurate heat loss calculation is knowing how much oil was burned, provided realistic efficiency numbers are assigned to each unit.

That is my preferred method as well.