Keystoker KA-6

Still shopping for coal boiler. Looked at a Keystoker KA-6. thing about it that i find... odd, is the size of the burn platform. its not very big, about 11" across(w) by about 18 inches long, it has forced air holes in it. Having a question about, its specifications.
Total Capacity Sq. feet of Radiation: 960

Recommended Load Sq feet of Radiation: 675

BTU Per Hour to nearest K: Net 122 Gross 144
How, does one figure total capacity Sq feet of radiation?? guy at store asked how many HW baseboard units were in current heating system for the house.

From what i see above this unit would never keep up with load demand on the boiler. Any one want to explain this some to me. Sting, you know, so how does one figure loads? I know about drafts, in houses, windows , doors, etc. and theres a factor for heat lose when calculating BTU inputs for total area., but Sq feet radiation is soething i need assistance with som. Thanks in advance.

Normally you should do a Heat Loss calc. for your house, that would get your close. How much is your existing boiler output? or do you know how much baseboard elements you current have? Most use 500-600BTU per Foot output. I believe there are link in some other threads for HEAT LOSS CALCULATOR. This has been discussed many times.

You might be surprised on the output. Coal is different than gas, oil, etc... My smaller coal stove only has a small 6" x 12" burn plate and puts out 90K btu's. COAL has a very high BTU output. So, you don't need much to get a lot of heat out of it. Plus with a boiler, you have a lot of volume to keep warm, once it gets warm, it doesn't need as much BTU, with coal, even at IDLE, it will keep the water up to a certain temp.

I know the Harmen VF3000 is rated like 95K BTU and states it will heat up to 3000 sq. ft. It all depends on your system, house insulation, windows, etc.....

What's your heat loss?

Don't forget that a coal boiler's output is 24/7 unlike an oil or gas unit that provides heat on demand. You always have a 40 plus gallon mass of water at 160 to 180 degrees on a K-6 size stoker. Don't sell any of the coal boilers short, they have an amazing output with the small amount of fuel they consume.
Read more on the forum, and forget everything you know about thermal mass, because if you go to coal, you will be in a different world as far as comfort goes. 'Low mass' is not in the coal vocabulary, so you have to readjust you 'Logic Control Center'.

OK, here ya go. I was about to delete everything in my reply. Someone beat me to it. Here's a chart I found with information you're looking for. http://www.crownboiler.com/educate/sizeheat.asp

ok, sat here did a lil head scratching. Looked up my baseboards,slantfins, 3/4 tubes, got heat btu output for them.next step go count BB units, lengths, multiply by BTU output per foot at what HW temp i would like to maintain with boiler. There also is residual BTU output for connecting tubes, found info for that based on ambient air temps enviroment it will be in (rooms/house). Pluus main feed/retun lines, which are insulated under house on long runs below floor joists, and feeder/return lines are in floor joist pockets, above insulation, but not insulated themselves to BB units.

I did all this when putting in new oil HWBB furnance 7 years ago, type house construction, windows, doors, drafts, wall thickness, insulation type r factor, etc, etc.. The heating system i have now works great, keeps house warm. But, fuel oil costs are making this fuel too exspensive use as primary fuel for heat.

Furnance in house now rated at Net ibr 132,000 BTU, with DHW coil,fuel use is about 4.5to 5 gals a day in the temps we been having highs mid 20's , lows -10 to 5 at night no winds. Use preset temps time of day thermostat for main house zone LR, kitchen, DR keep at 62 work hours, and sleeping, set for 67 when at home in moring, and evenings. upstairs zones are left at 62. except when windy out at night bump up to 67.

Well you have reached the crossroads (pun intended) that most of us have. Present heating system works fine but fuel costs are killing you. You'd never regret installing a coal boiler. Sounds like you are doing your homework calculating the load etc. It is important to size the boiler correctly. Oversized wastes coal, undersized runs its butt off and never catches up.

One thing though, please don't call your boiler a furnace. It's a technicality but a furnace makes hot air and a boiler makes hot water.

I'll never quite understand why the typical advice given to someone who is replacing an existing boiler that has a known BTU input/output, and which has served to heat a home for perhaps years to decades is to perform heat loss calculations before determining the output BTU's for a replacement boiler. For the case of direct replacement, unless perhaps it is perceived that the original boiler was oversized to begin with, why wouldn't it be generally acceptable to purchase a coal boiler with as close to the same output BTU's as have worked well for many years in the past? Is there something different that needs to be considered between the output BTU's for say an oil fired boiler vs. a coal fired boiler?

lsayre wrote:I'll never quite understand why the typical advice given to someone who is replacing an existing boiler that has a known BTU input/output, and which has served to heat a home for perhaps years to decades is to perform heat loss calculations before determining the output BTU's for a replacement boiler. For the case of direct replacement, unless perhaps it is perceived that the original boiler was oversized to begin with, why wouldn't it be generally acceptable to purchase a coal boiler with as close to the same output BTU's as have worked well for many years in the past? Is there something different that needs to be considered between the output BTU's for say an oil fired boiler vs. a coal fired boiler?

The best answer to that question may be two examples recently posted here.
And this is in no way a dispersion to folks asking questions - its just an entitlement to the question above.

One good one is the opening of this thread - is there any indication of the load the specifications point to?

The second is a line of the opening of a similar thread this week
"my question is will the e·f·m Coal Stoker Boiler DF520 handle 3420 Sq FT."

Do you note that anyone can say yes or no to either of these?

Your also on the nose with your suggestion that the current appliance may not be correctly sized - most likely its too large - and that's not a good feature to have in the basement with solid fuel. If we force folks to begin to do their own research and development - its far more likely they will arm themselves with the correct knowledge to get a proper installation and functioning system - vs being the next victim of an online salesman who needs to move an XYZ machine this week - or the lowest bidder with a pipe wrench.

Much like your doing.

Kind Regards
Sting

Other than the comments above posted by Sting, I'll add these:

lsayre wrote:I'll never quite understand why the typical advice given to someone who is replacing an existing boiler that has a known BTU input/output, and which has served to heat a home for perhaps years to decades is to perform heat loss calculations before determining the output BTU's for a replacement boiler. For the case of direct replacement, unless perhaps it is perceived that the original boiler was oversized to begin with, why wouldn't it be generally acceptable to purchase a coal boiler with as close to the same output BTU's as have worked well for many years in the past? Is there something different that needs to be considered between the output BTU's for say an oil fired boiler vs. a coal fired boiler?

When the house was originally built, was an accurate heat loss calculation made?? Typically not.. heating units were almost always oversized because NO builder would want to get a call saying the house won't stay warm, and he needs to 'fix' it.. so oversize units were installed..
Also, the heating units were often sized for the worst weather in the area.. say for the once every two years, -20* night.. but most of the time the lowest temperature would be +10*.. so, again an oversize heating unit was installed.. just to save from having a 65* house one night every two years..

And,, what has happened to the house since it was built?? Better windows and doors installed??? better ceiling/attic insulation?? How about new siding with Tyvek-type house wrap installed.???

And and all of the above improvements could drasticly reduce the BTU requirements to the house..

Now, on the opposite side.. how about added square footage added? an Attic converted to bedrooms? an addition added ??

For us on the forum, it would be quite irresponsible to suggest to just go with the original sizing of the heating unit..

Most of the time a smaller coal burning unit with some modern improvements in the house's insulation/windows, will net a big savings in the purchase price of the smaller coal burner,, and since this is usually a homeowner decision, an ocassional night where the heater runs 100% and the house doesn't quite make desired temperature, well the homeowner knows that he needs to do some caulking or window/insulation improvements..


Greg L

Hey! Did 'sting' get a new assistant in the shop? The grumpy ole man with the "V" plow must have gone to Hugh's LA party and brought back some of the pills with the big "V" on them! I'm sure he will call her his "closely spaced 'T's' live working model". Crafty, stinger!!!! NO HEAT LOSS THERE!!!!! Reach for the PRV......

Sting and Greg, your points are well taken! I had a sneaking suspicion that the main reason for the calculations was to downsize the new coal boiler (though obviously in some cases such as home additions, etc... up-sizing may be called for). An additional example for the boiler up-sizing case would be if the coal boiler is going to be called upon to provide all of the homes DHW, whereas the previous boiler was not used for this purpose. Is there a nominal method to calculate the additional hourly BTU demand from a boiler that it called upon to provide a homes DHW? Assuming for example the case for the nominal families need of 80 gallons of 125 degree F. hot water per day, and incoming water at 55 degrees F.

Based upon a few knowns for this example, I can calculate the following BTU requirement, but I don't know if this is to be considered directly additive to the boilers BTU's required to heat a home or not:

8.33 lbs/gal x 80 gal. x 70 degrees of required H2O temp rise = 46,648 BTU's required to heat all of the homes hot water for one day.

What it "boils" down to is this question:

If a fair assumption can be made that all 80 gallons are generally consumed in a time span of only one hour out of a 24 hour day, and if a heat loss calculation for a home dictated a 75,000 BTU boiler, then do you just add 75,000 and 46,650 BTU's to get a boiler sized at a required BTU output of about 122,000 BTU's, or in this case would the boiler be oversized by about 47,000 BTU's for all but one hour of every day?

Do not directly add the domestic hot water load to the boiler heating load.

There is a thing call diversity that is not easily defined. To add the load would assume you used your maximum average dhw during the same time the outside air was at it's coldest. This could only happen less than 2% of the year.

First of all, you must oversize the boiler to account for piping and pickup losses. This is what the Net IBR rating is on oil and gas boilers. Coal and wood boilers are not rated as IBR output. Piping losses are to unheated spaces such as crawl spaces and basements. Pick up is a factor to permit the boiler to have extra capacity to bring up the space temperature such as when you come out of setback. IE: You leave for a night out and turn down the thermostat. You get home and turn the thermostat back up. You want the house heat to recover in a reasonable period of time.

Domestic hot water imposes only at temporary load on the boiler. You may have one or two peak hours during the day, but the house heat load can coast for a little bit. I would oversize the boiler but not add the load directly, unless that load was greater than the heating load. I am sure there as some guidelines out there but I would add about 15,000 btuh to the boiler capacity if I were heating normal DHW loads. This number could be alittle more or less depending on the number of bathrooms, etc. you have.

Do this,
1. Figure you house heat loss with at least a 10% safety factor.
2. Make sure your radiation can deliver this heat load.
3. Add 15% to the heat loss on top of the 10% safety factor.
4. Add 15,000 BTUH to this number for added capacity.
4. Use this number and select the boiler with an output of this number or greater (net out, not ibr out).

If you have 75,000 btu of heat loss with a safety factor, you need a boiler capable of at leat 86.2 mbh out for heat plus 15 mbh for dhw extra. This accounts for a total load of 101.2 mbh output.

You are a little light with a kaa-2 even if you didn't heat DHW. A KA-6 is the right size boiler for this loss. It will coast along just fine and have plenty of capacity.

lsayre wrote:Is there something different that needs to be considered between the output BTU's for say an oil fired boiler vs. a coal fired boiler?

I agree with steamup that there are good reasons for oversizing a coal boiler somewhat relative to whatever the heat loss computations may show. The rated capacity of the boiler is based on assumptions that may not be fully valid at the time you are looking for the boiler to deliver its maximum output. For example:

- sizing of coal - In my old house, a refurbed EFM 700 stoker had trouble carrying the load when it was really cold. Eventually I figured out that much or perhaps all of the issue was the fact that I was burning rice rather than buck (not available locally), which EFM originally specified for this unit. If the coal being used is the wrong size, or has too large a percentage of undersized pieces, the boiler may not achieve its rated output.

- clinkers - For a while I used red ash coal in an Alaska 140 (w/paddle stokers). When I tried to crank it up in cold weather I had problems with clinkers and "plowing". To the extent you have to limit air to the fire to control clinkers, at least in a flat stoker, you may be holding it back from its maximum output.

- boiler maintenance - Burning coal generates fly ash, and boilers need to be cleaned periodically to ensure that accumulated fly ash does not interfere with efficient heat transfer, draft, etc. If that cold spell hits before you do your mid-season cleaning, your boiler may not be able to perform up to its ratings.

- DHW - As covered in detail in other threads, it takes something like 40k btu/hr of boiler output to maintain a 1 gpm stream of DHW output. If you make DHW from your boiler, you need to be able to cover the load associated with all of the showers, dishes, laundries, etc. that need to be done while you're counting on the boiler to also cover the max heating load. I agree with steamup that the heating load can "coast" to an extent, but if you use a lot of DHW the numbers can get big fairly quickly.

Now older - not sure about wiser - I take comfort in relying on a stoker that I only have to run at about 70 percent of its capacity to make all of the heat and DHW that we normally need. It held the set temp at -21 deg, and had some in reserve for contingencies. So I guess my suggestion would be to do all of the load and heat loss computations you wish based on the things that you know, but don't be afraid to throw in a contingency for the things you don't yet know about how your system may actually perform at any given time under a heavy load.

Mike

Many thanks steamup!

I was going to replace my oil boiler with a Kaa-2 (after first suffering the wrath of the gods from the lady of the house when I was initially pursuing a coal stove for the living room), but then along came the idea to heat DHW, and then I discovered that bulk rice coal is not available at the closest anthracite dealer who will deliver to me, but bulk pea coal is readily available for delivery, and suddenly it all added up to an AHS S130 Coal Gun. If all goes as planned, the Coal Gun should arrive at my house this week Wednesday. It has a rated 130,000 BTU's of input, and at 80% efficiency, that would be about 104,000 BTU's/hr of output. Since my old dinosaur oil boiler died I've heated my home for 4 winters (and I'm currently in the 5th) with only my 22.5 KWH back-up resistance boiler. At its 22.5 KWH rating that translates to about 77,000 BTU's/hr. The resistance boiler has done quite well overall, with only the very rare -10 degree or so days here resulting in a bit of a struggle to maintain a full 68 degrees across all of my zones. So I'm hoping that the Coal Gun should be able to heat the home and provide for DHW in my case.

Here is another cheaters method that can be used to calculate a homes heating BTU requirement without doing a heat loss calculation. It is often said that for electric baseboard heat a simple rule of thumb is that 10 Watts of baseboard heating output are required for every square foot of area to be heated. My house has 1,680 sq-ft upstairs and a downstairs family room of 840 ft-sq. Total = 2,520 ft-sq. 2,520 x 10 watts = 25,200 watts = 25.2 KWH (a bit higher than my resistance boilers 22.5 KWH, but my family room is a finished half of the basement, so perhaps its being partially underground saves a bit on BTU's (????). In any case, at 3.412 BTU's per watt, 25,200 watts = 86,000 BTU's. Again, that is below the 104,000 BTU's of output for the Coal Gun, so a safety margin of 18,000 BTU's is available for the DHW using this method (again in my case only). 18,000/86,000 = a 21% safety margin.

baseboard HW units output is given in BTU output per linear foot, not square feet. do they consider it a Sq foot because of the radiation fins on the tubing?
If not, then there is a lot of measuring and squaring to figure sq foot load, verses input BTUs from boiler to make exsisting system work properly based on heat loss calculations from 7 years ago.