How to Know If I'm Getting 100,000 BTU's From My Stove?

First of all, Happy Thanksgiving to all!

There is so much knowledge to be gained here, I need some. I've been roasting coal for 27 years now, 1st an EFEL now my ALASKA KODIAK.

My question is, 'how do I know if I'm running at full efficiency?' How do I know if I'm getting the most heat from the stove or sending it up the flue?

With my air shutter fully open and the MPD fully closed, my stove temp is 300 measured on a flat side at the level of the red coals and the stack temp is 150 8 inches above the exit and right below the MPD.

If I crack open the MPD, stove goes up to 350 and stack to 200. Where is the point of diminishing return?

I have what I would call perfect draft conditions, it can run it in 65 degree rainy weather with no visible red coal and it stays running at 100 degrees stack temp. I have a baro about 2 feet above the MPD, and it seems to work quite well on windy days.

The pictures show my configuration. My lovely wife has allowed me to alter/adorn the stove with heatsinks and fans to pull as much heat as possible off the box.
The muffin fans are 230 volt, they run silently on 115. The 20" box fan has a Lutron dimmer, it idles when we're in the room but we turn it up overnight. That fan feeds into a plenum I made to funnel air down to the inlet where the factory screaming blower would attach. The other half of the plenum feeds up to yet another heatsink mounted to the back wall of the stove. It's so great not to worry about creosote by cooling the sides and extracting as much heat as possible.

YES, I know the ozone generator is not a good idea, but it really attracts the coal dust/fly ash. I clean it every few days and marvel at what would be elsewhere.

I hope I covered everything... How do I measure/guess at the BTU output?

Thanks in advance.

YES, I know the ozone generator is not a good idea, but it really attracts the coal dust/fly ash. I clean it every few days and marvel at what would be elsewhere.

I think it is a great idea and I use one similar to yours and clean it every morning. It lives near my new (to me) Jotul 507

How to know if I'm getting 100,000 BTU's from my stove?

If your daily coal consumption is about 280 pounds, and your stove is 70% efficient, and the ash generated by burning it looks respectable, you have likely achieved 100,000 BTU's per hour of average output for one full day.

That would require adding 50 pounds of new coal to your stove at intervals of roughly four and a quarter hours.

To measure your hourly BTU output you must know your hourly burn rate and your stoves efficiency.

For the case of burning 50 pounds of coal over 24 hours at 70% output efficiency you are achieving an average hourly BTU output rate of:

50/24 * 12,250 *0.70 = 17,865 BTU's per hour

It is very tough to accurately measure the actual BTU output of a stove. Larry's mention of coal consumption is about as close as you are going to get. Generally speaking, if the stove is heating your house and you can keep the stack temperature low...you are doing fine.

Forum member "gizmo" recently posted this in another thread, I thought he did a fine job of summing it up.

gizmo wrote:The one thing I learned about BTU's is, If you don't have enough, you will be cold.

Gizmo has nailed it!

Your stove is beautiful! Your modifications show a high level of handy work!

You are burning bit coal? I only ask because of the creosote mention. Maybe you burn some wood at times?

In all honesty I would say Larrys "equation " is about as good as any for a general idea of the btu's. For me it's just a number to compare stove sizes too in particular for hand feds. I always look at how many pounds does the stove hold in a full load and then how hot it gets versus the stack temps in my situation. I find it interesting that at "full throttle"you only get 350/150. That's good stove to stack numbers but if I opened my primaries all the way I think I could get 700/175 numbers on a cold day. I don't run it that high, I like to stay about 550r so max and normally just cruise at 350-400 during the winter but that is with the primaries maybe a 1/2" or so open. Maybe it's the heat sinks you have attached to yours?

Nice set up by the way and a happy Thanksgiving to you and yours.

A 100,000 BTU is an enormous amount of heat.. To make it more understandable just how much heat that is, I've concluded the following.

100,000 BTU is enough heat to raise roughly 120 gallons of water 100 degrees. Imagine raising the temperature of a 120 gallon tank of water from 40 degrees to 140 degrees IN 1 hour!

Of course this hinges on me doing my math right

The math is right. Either that or we are both making the same mistake.

lsayre wrote:The math is right. Either that or we are both making the same mistake.

Thanks Larry

lsayre wrote:Your stove is beautiful! Your modifications show a high level of handy work!

Thanks for the compliment and the formulas. Shoveling 280 lbs. per day sounds like I'd be feeding a locomotive! I use about 40 lbs./24 hrs. for these temps. I guess 100,000 can never be reached, and would be unnecessary.

I like the statement about if you're cold, you need more BTU's. Makes sense.

After reading the responses so far maybe my better question would be 'Do I have a good stove/stack temperature ratio? I think so, and at a certain point there has to be a increase in stack temp for box temp, not necessarily linear though?

After drilling the first hole, installing the heatsinks and proving to my skeptical inspector/wife that we wouldn't die of CO poisoning, she kinda gave me free reign of experimentation. I think she realizes the savings now that oil is $3.49/gallon that a couple $14.95 fans and the few watts it takes to run them quickly turns into savings.

We haven't had the oil on yet here, overnight room temps are 75 near the stove to 68 in bedrooms far away while it is below 30 outside. The house is comfortable, I think I've reached coal nirvana...

Thanks again. John

SteveZee wrote:You are burning bit coal? I only ask because of the creosote mention. Maybe you burn some wood at times?

In all honesty I would say Larrys "equation " is about as good as any for a general idea of the btu's. For me it's just a number to compare stove sizes too in particular for hand feds. I always look at how many pounds does the stove hold in a full load and then how hot it gets versus the stack temps in my situation. I find it interesting that at "full throttle"you only get 350/150. That's good stove to stack numbers but if I opened my primaries all the way I think I could get 700/175 numbers on a cold day. I don't run it that high, I like to stay about 550r so max and normally just cruise at 350-400 during the winter but that is with the primaries maybe a 1/2" or so open. Maybe it's the heat sinks you have attached to yours?

I'm burning purely Blaschak pea anthracite. Never wood/bituminous. Very predictable and stable.

I think tonight I'm going to shovel a light layer on top of the hopper fed level to see if it brings it up a bit? With the angle of the fire-brick that would give a larger surface area of red coal. If that's the case, since the hopper is slightly tapered inward, a shorter hopper would achieve the same effect making a larger firebox? I think I'll leave well enough alone there. No turning back on that one...

In a different thread (topic/subject) I inquired if I could burn pea in this stove, and it seems from the replies that you can but it will likely never reach sufficient temperatures in the dead of the winter in most home settings on strictly pea. To get it up from 300 degrees to 500 degrees or so will most likely require burning nut. With nut you should generate loads of additional heat. I'm not speaking from direct experience here, but I welcome that anyone with direct experience should jump in and correct me or confirm this.