recovery rate

hello everybody i just installed a keystoker kaa-2 in my 2000 sauare foot ranch. just wondering on what the recovery rate would be to bring back up to temp. for example boiler is running about 175 circulators kick on drops temp to about 155 then starts to climp when the coal boiler starts to stoke takes about 20-30 minutes to recover with the circulators running. does that sound like it is taking to long.

second question

would i use more coal if i have slower stoker rate for a longer time to bring temp up or a faster stoker rate for less time?

If the stoker runs when there is a call for heat below the high limit you may have an undersized boiler. I think that is the little one, about 75,000 BTUs. What is your oil/gas unit rated at? I have a 2200' house and the boiler is rated at 139,000 BTUs net. I know my house is a bleeder but would think you would need at least 100-120,000 BTUs even with good insulation and windows. Your also in a colder area than me.

I would increase feed rate one turn at a time giving 12-24 hours between increases to see results. If after 20 minutes of continuous stoking you do not have a full grate of fire within about two inches of the end of the grate you have room to increase your feed rate. I don't know what uses less coal but a 20 minute recovery is too long in my opinion.

Coaled Sweat,

What size nozzle (how many gallons per hour) is on your oil burner? That is what counts.

Mike

If the boiler were undersized, the water temp. would not be climbing back up with the circulators running. Drops in tank temperature are a fact of life with these types of units, it takes time for the fire to build up and to die down, unlike a gas or oil system where the flame is instantaneous. One possible thing to try is to keep a larger maintenance fire (less time to build to a larger fire). Feed rate speed will not have an effect on your consumption, as it still takes Xamount of time for the coal to burn.

Mike

Complete Heat wrote:Drops in tank temperature are a fact of life with these types of units, it takes time for the fire to build up and to die down

I don't think the circulators are running for 20-30 minutes continuously. If they are, he has other problems. I would think a stoker should out perform my hand fired boiler. It has no trouble maintaining a fairly even temp.

I have never owned a stoker, nor do I claim to know anything about them. I have many years experience operating and maintaining industrial steam boilers up to 500HP. This does not sit right with me. It is either improperly adjusted for draft/stroke bigtime, or its undersized. From the description, gt750 says it runs down from the high limit to the low and takes 20 minutes to recover. I am assuming that this happens in a continuous cycle. Ideally, a boiler should be running as hard as it can without hitting its high limit. This matches the firing rate to the load, it doesn't matter what the fuel is. If this thing is being stoked and a blower running continuously once it falls below the high limit and runs down to the low limit before it starts to recover, its going to be too small when the temps hit the minus column.

Am I missing something about stokers

"20-30 minutes to recover with the circulators running" sounds right to me. When the oil burner guy was sizing a new boiler for my house, he talked about the theoretical ideal of minimizing off time, i.e. when perfectly sized the burner would run all the time but at a low(er) rate. I think that's saying much the same as coaledsweat's statement about matching the firing rate to the load. Of course coal will take longer than oil to recover, because it's not instant-on like oil. But if your boiler recovers back to 175, AND THEN MAINTAINS 175 while continuing to supply heat to the house, then I don't see that you have a problem.

What you didn't say is, is it keeping the house comfortable or not?

coaledsweat wrote:Am I missing something about stokers

You got it right.

From Keystoker's web site the KAA-2 has a 480 sq. ft. specification. Likely much to small for your 2000 sq. ft. ranch house, unless it's super, super insulated. It's Keystoker's smallest boiler.

rberq wrote:But if your boiler recovers back to 175, AND THEN MAINTAINS 175 while continuing to supply heat to the house, then I don't see that you have a problem.

That was my point. From his post it seemed like it didn't maintain the temp. Instead, it continues to fall to the low limit and then struggle to get back to the high limit.

If it is undersized, a heat recovery system would make that easier to live with and keep you warm when the temps drop if you can't return it for a bigger one. Its actually more efficient to run a small boiler very hard as opposed to a large one idleing.

hello everybody first off i would like to thank everybody for there input it has been a great help. i dont think the boiler is too small because it has 90000 btu gross while my oil burner was 100000 gross btu which i had way under fired. as for the slow recovery i have to agree with reberq and complet heat this is a solid fuel and takes a little to get going. but once the fire is up and running i have no problem holding temps 0f 170. i have since made some adjustments since i made the first post i did increase my maint fire and turned the stoker in 1 more turn. i still have 4 turns to go to full stoker. it seems to be working good i cant complain i am burning about 35-40# of coal in a 24 hour period so my boiler runns for 4-4.5 days on a hopper now ony if the ash bin was bigger it would be pretty maint free for a four day strech. if anybody has any other ideas i would love to hear them i am new at this and all help is greatly appreciated. if somebody else is running a kaa-2 i would like to compare settings and ovealll running.


thanks chris

I think you found the issue and are making the right corrections, 35 to 40# per day is only 24,000 btu per hour at best. You need to keep tweaking it up to increase the coal feed, when the weather is cold you should be using closer to 75# per day and maybe more.

Just my opinion based on the simple numbers, coal is 14,000 btu per # for the really good stuff, so you are doing well to heat your house with that amount of coal.

Yanche,

Keystoker rates their boilers on "load square feet". which is different than square footage of the house. Load square footage is determined by how much baseboard their is in the house. The KA-2 would be able to heat my house (3,200 sq. ft.), so while the KA-2 is Keystokers small unit, it is quite a capable unit.

Mike

Complete Heat wrote:Yanche,

Keystoker rates their boilers on "load square feet". which is different than square footage of the house. Load square footage is determined by how much baseboard their is in the house. The KA-2 would be able to heat my house (3,200 sq. ft.), so while the KA-2 is Keystokers small unit, it is quite a capable unit.

Mike

What's deceiving is that they do in fact rate them as you say, however their chart says it is for "square feet". Obviously, the chart is labeled wrong by looking at the BTU ratings.

http://www.keystoker.com/coaloilboilers.html