Hotblast Year 3

CoalisCoolxWarm wrote:Ducted heat supply, right?

If you're using Bit coal, it is possible to have a "cool" fire and never quite get over that threshold to have good warm air in the ducts.

What are the settings on your blower control? The dial that controls the turn on/off blower...

If that is too low, you'll get some heat, but the fire needs some heat to get a good, efficient burn.

I used to set mine higher and let it run lower so the fire would build up before blowing. Something like 120F - 140F to start and then down to maybe 110F to stop might work?

Where are you getting coal? The "best" bit I had came from Valier's, just above Punxsy. It was a recommendation from guys here, which made a good difference in heat output.

I appreciate your questions, CoalisCoolXWarm.
It is ducted.

However, my measurements are right at the top of the furnace.
Ductwork doesn't seem like it should enter in to this yet.

The blower settings are whatever the factory set was.
I think 140.
They run almost constantly.

What is a "cool" fire?
As I mentioned above, yesterday, inside the furnace my IR gun wouldn't read because it was over 1000.
The face of the furnace above the load door was 350 and the supply pipe was only 110 6" above the furnace outlet.

I'm going to apologize if the following makes me look like a butt head.
Obviously, I don't know much of anything and am looking for answers and appreciate any and all suggestions.

The coal this year came from McIntyre's tipple in Shelocta.
This is the 3rd supplier in 3 years of operating my stove.
I'm sure Valier has fine coal.
But, like McIntyre, they buy their coal.
Possibly from the same place.
I don't know.

As I recall, I called Valier last year on your recommendation.
They had the same coal as the other places.
I'd have to check but I seem to remember it was Upper Kittanning.

I believe all of that kind of coal has about the same specs for BTUs, ash, sulfur, etc.

I couldn't see going an extra 30+ miles one way to haul coal that seemed, to me, to be about the same.
I could be wrong.

But, I don't think my problem is coal when I get fire as hot as I am.

The loss of that heat from the firebox to the supply seems significant

Sunny Boy wrote:Larry,

Your stove and duct temp readings seem kinda low to me for trying to heat a whole house.

Do you have any readings of temps in the same places from the old coal furnace to compare to ?

How do the firebox sizes of the two furnaces compare ?

How about the surface square area of the heat exchangers ?

Any duct fans ?

If your present furnace's firebox, and/or, heat exchanger are even just slightly smaller than the old one, you'll have to run this one hotter to make up to difference.

Paul

Thanks, Paul.

The old furnace has been gone for over 40 years.
It was a big one but I don't know or remember BTU rating or firebox size.
Reaching way back into the recesses of my memory, the fire box was way bigger.
I have no duct fans other than the two blowers on the furnace.
I don't have a plenum.
Just 2 8" pipes that hook into my existing ductwork

Dieselpowerf350 wrote:How close is it to your regular furnace? Just the blowers on the back might not be enough to push it through your house. Mine will heat the duct up some, then the big blower from my oil furnace will turn on and push the air through my duct work.

Thanks for weighing in, dieselpowerf350.
The coal furnace is about 30' from the propane furnace.

I'd thought about turning on the blower for the propane to run all the time.
Decided against it because I thought it would blow cool air when the coal fire burns down.

You may be right about the blowers but they were the ones specced by the manufacturer.
And I still have those low temps coming right out of the furnace.

This may be dumb sounding but it's like the heat exchanger isn't working properly

larryfoster wrote:

Sunny Boy wrote:Larry,

Your stove and duct temp readings seem kinda low to me for trying to heat a whole house.

Do you have any readings of temps in the same places from the old coal furnace to compare to ?

How do the firebox sizes of the two furnaces compare ?

How about the surface square area of the heat exchangers ?

Any duct fans ?

If your present furnace's firebox, and/or, heat exchanger are even just slightly smaller than the old one, you'll have to run this one hotter to make up to difference.

Paul

Thanks, Paul.

The old furnace has been gone for over 40 years.
It was a big one but I don't know or remember BTU rating or firebox size.
Reaching way back into the recesses of my memory, the fire box was way bigger.
I have no duct fans other than the two blowers on the furnace.
I don't have a plenum.
Just 2 8" pipes that hook into my existing ductwork

That right there could be the difference. The old furnace could produce more heat volume without having to run hard.

Think of BTUs as "heat volume" not temperature. Then look at your situation in the extreme. Say you have a group of one hundred pieces of coal burning at a set temp. Then you have a group of same sized coal burning at the same temp, but it's 1000 pieces. Which group is going to give you more heat "volume" (BTUs) ?

To get the one hundred group to equal the heat volume of the 1000 group you have to make it burn hotter to increase the heat volume.

Since you can't get your furnace to be "way bigger", to get the heat volume the old furnace had, you have to get your furnace's temps, "way hotter" to make the same BTUs. And when said you've run your furnace hotter it showed that works.

Paul

Another way to think about it is, BTUs are just a measure of "heat" volume (not temperature) to raise one pound of water one degree F.

It doesn't matter if you use a bunch of candles, or one small oxi-acetylene welding torch. If they both raise that pound of water one degree they both put out the same BTUs,..... even though the torch flame burns a few thousand degrees hotter than a candle flame.

You can't have the heat volume of a lot of candles, so go with a hotter fire in a smaller space like the torch.

In other words, crank it up and kick back !

Paul

Thanks for those examples, Paul.

Please clarify something and type real slow for my simple mind.

I keep getting stuck at the furnace.
The heat isn't even getting to the ductwork to heat the house adequately.

90K BTU propane furnace 80% efficiency heats the house adequately.
135K coal furnace at, let's say, 50% efficiency is roughly the same heat volume.
My house is warmer with the propane with about the same volume.

I also lose 900 (or so) degrees from the firebox through the heat exchanger when it reaches the supply right at the furnace.
This is before it ever has a chance to get to the distribution through the duct work.

I can't find a picture that shows me how air moves through my furnace

larryfoster wrote:Thanks for those examples, Paul.

Please clarify something and type real slow for my simple mind.

I keep getting stuck at the furnace.
The heat isn't even getting to the ductwork to heat the house adequately.

90K BTU propane furnace 80% efficiency heats the house adequately.
135K coal furnace at, let's say, 50% efficiency is roughly the same heat volume.
My house is warmer with the propane with about the same volume.

I also lose 900 (or so) degrees from the firebox through the heat exchanger when it reaches the supply right at the furnace.
This is before it ever has a chance to get to the distribution through the duct work.

I can't find a picture that shows me how air moves through my furnace

Apples to oranges.

First off,.... from what guys who know more about the process say, don't believe the BTU numbers of modern coal stoves. They say that more realistically the BTU you can expect are closer to half the plate rating.

Secondly, that coal furnace is very likely rated at it's maximum output, but, from the temps your posting, it sounds like you've got it dialed back more than what it can do running at max.

Third, your propane furnace has one burner setting and it only adjusts burn time, not flame volume like you can do with the dampers on the coal furnace.

You mentioned that you've had higher output temps from the coal stove being run hotter. So, If you were to open the dampers and run the coal furnace at, or very near to, it's maximum, it would likely come closer to what you think it should be doing based on the numbers on it's rating plate.

Paul

Thanks for your continued patience, Paul.
I'm pretty thick
I put my replies in italics below.

First off,.... from what guys who know more about the process say, don't believe the BTU numbers of modern coal stoves. They say that more realistically the BTU you can expect are closer to half the plate rating.

So, my 50% efficiency guess to get around 63K BTUs output is more than I should expect?

Secondly, that coal furnace is very likely rated at it's maximum output, but, from the temps your posting, it sounds like you've got it dialed back more than what it can do running at max.

I don't have anything dialed back.
I usually have the spinner primary air open as far as it will go.
The only way to get it real hot is to open the ash door.
Then I need to keep watching it so it doesn't get too hot

Third, your propane furnace has one burner setting and it only adjusts burn time, not flame volume like you can do with the dampers on the coal furnace.
As mentioned above, I don't have any dampers to open.
Other than the spinner on the ash door, the only thing I can open is the ash door

You mentioned that you've had higher output temps from the coal stove being run hotter. So, If you were to open the dampers and run the coal furnace at, or very near to, it's maximum, it would likely come closer to what you think it should be doing based on the numbers on it's rating plate.

Only thing I have left to open is the ash door.
Then it becomes a full time job monitoring to be sure it doesn't get too hot

Another issue that may be a contributing factor is that the built in air feeds aren't adequate to get hot fires.

As I mentioned, the only way to get I can get hot fires is to keep the ash door open.
Otherwise, it maxxes out at much lower temps

Ok. I thought you mentioned higher temp numbers, but I see now you also mentioned the door needing to be open. "If I really work on making the furnace really hot by opening the ash door and get the front of the furnace to 500-700, I can get that temp inside the supply pipe to 150-160 up to 200. "

300-ish F over a load door doesn't seem like much to me for a coal furnace.

It could be that with one spinner there is a either a design shortcoming in that furnace, and/or, the chimney system draft is on the weak side and it needs another spinner damper to let it reach it's potential output ? Do you have a mano gauge hooked up ?

Is your house relatively air tight ? How does the stove act if you crack open a basement window ?

As to BTU ratings, I only know what's been said many times on here over the past 3 years when the topic of BTU ratings of coal stoves comes up - that is to not believe them. Some say they are so far off that it's more realistic to halve them. Maybe someone more in the know will jump in for that one. I do know that a UL listed stove is not rated under your conditions, but what that stove will do in a test lab. Real-world results will vary greatly - especially if your chimney system has a weaker draft strength coupled with possibly a too-small primary air inlet.

Yes, running a coal, or wood stove at it's max can be nerve racking and stressful on you and the stove. And, you'll have to refuel more often. That's why, unlike sizing a wood stove where you don't want it too big, it's wise to get a coal stove that seems to be more than needed. Run a big wood stove slow and you risk building up creosote. Run a big coal stove slow and the coal lasts longer.

Paul

Ok. I thought you mentioned higher temp numbers, but I see now you also mentioned the door needing to be open. "If I really work on making the furnace really hot by opening the ash door and get the front of the furnace to 500-700, I can get that temp inside the supply pipe to 150-160 up to 200. "

300-ish F over a load door doesn't seem like much to me for a coal furnace.

It could be that with one spinner there is a either a design shortcoming in that furnace, and/or, the chimney system draft is on the weak side and it needs another spinner damper to let it reach it's potential output ? Do you have a mano gauge hooked up ?

Yes.
It, typically, sits at .5 (or -.5)

Is your house relatively air tight ? How does the stove act if you crack open a basement window ?

Not real tight in the basement.
The outside basement door has a 1/2" crack on the edge between the door and jamb

As to BTU ratings, I only know what's been said many times on here over the past 3 years when the topic of BTU ratings of coal stoves comes up - that is to not believe them. Some say they are so far off that it's more realistic to halve them. Maybe someone more in the know will jump in for that one. I do know that a UL listed stove is not rated under your conditions, but what that stove will do in a test lab. Real-world results will vary greatly - especially if your chimney system has a weaker draft strength coupled with possibly a too-small primary air inlet.

Yes, running a coal, or wood stove at it's max can be nerve racking and stressful on you and the stove. And, you'll have to refuel more often. That's why, unlike sizing a wood stove where you don't want it too big, it's wise to get a coal stove that seems to be more than needed. Run a big wood stove slow and you risk building up creosote. Run a big coal stove slow and the coal lasts longer.

Never too concerned about using more coal to a certain extent.
Don't want to run at unsafe levels.
I do run it with the ash door open for short periods.
Usually, in the morning to get the temps back up.
But, I check it at 30 and 45 minutes because the fire is plenty hot

One other thought, Larry.

You say the furnace has two 8 inch uninsulated hot air outlets. Where do they connect to the original duct work leading to all the rooms - and how long of a run are they ?

Paul

Hey Paul, just to keep things in perspective.... I'm using the same furnace. My current stats are,

385 over the load door
286 flue pipe, 2 ft from breech
122 warm air supply
73 average house temp
15 degrees outside

I'm at 12 hours since last tending and the thermostat is calling for heat (hence the elevated temps). The fire has at least another 6 hours of heat output before it will start to wane.

The kicker of the whole thing is that I'm heating 2400 square ft compared to his 1000. I should also add that I'm using ~65 pounds per 24 hours for the current heat demand.

Larry, it would help to know how much coal you are burning (accurately) per 24 hours.

Also a thing to consider is the volume of air flow of the warm air supply. His could be less or more than mine just because of resistance in the duct work. His could be heating less air to higher temps which would net out the same as (mine) heating more air to lower temps.

I agree that adding another primary air control to the ash door would reap huge benefits.

Larry, we've been over this pretty extensively in the past. If I remember correctly, it seemed to me that you get short bursts of heat but it doesn't last, and I think this is why your overall house temp isn't satisfactory.

Get a two inch hole saw and cut another primary air control into that ash pan door. If you can burn 70 pounds a day I bet your house will be toasty.

Those tiny points of combustion where you read over a thousand degrees aren't gonna make your warm air supply a thousand degrees. It just doesn't work like that. The heat that the fuel bed produces gets spread out over the surface area of the fire box. The BTUs aren't lost, they are spread out. Same with the propane furnace, I can't guess what the temperature of burning propane is but of course you can see where I'm going with this.

You say the furnace has two 8 inch uninsulated hot air outlets. Where do they connect to the original duct work leading to all the rooms - and how long of a run are they ?

Each is 2 joints of pipe and 2 elbows.
6'?
Initially, it went straight up into the duct before I put a return on.
Had to move the furnace to put a return on,

Lightning wrote:Hey Paul, just to keep things in perspective.... I'm using the same furnace. My current stats are,

385 over the load door
286 flue pipe, 2 ft from breech
122 warm air supply
73 average house temp
15 degrees outside

I'm at 12 hours since last tending and the thermostat is calling for heat (hence the elevated temps). The fire has at least another 6 hours of heat output before it will start to wane.

The kicker of the whole thing is that I'm heating 2400 square ft compared to his 1000. I should also add that I'm using ~65 pounds per 24 hours for the current heat demand.

Larry, it would help to know how much coal you are burning (accurately) per 24 hours.

Also a thing to consider is the volume of air flow of the warm air supply. His could be less or more than mine just because of resistance in the duct work. His could be heating less air to higher temps which would net out the same as (mine) heating more air to lower temps.

I agree that adding another primary air control to the ash door would reap huge benefits.

Lightning, thanks for sharing that info.
Looks like over fire and supply temps are similar.

To answer your question would take a SWAG estimate unless I waited 24 hours.
I'm guessing each shovelful of coal is 5#.
I'm thinking 12 shovels for the day
I add 3 times per day which is way less than previous years.
Morning (8ish AM) 4 shovels, late afternoon (4-5) 3-4 shovels and bedtime (10:30-11) 4-5 shovels.
Each time I shake and empty ashes and poke and push hot coals to the back and fill the front to the top of the bricks.

I can stretch to 12 hours if I reduce the air a little.
At night, I close the spinner to between 2-1/2 -4 turns open depending on how cold it is out.

I think I saw somewhere that you drilled a hole in your door for an additional air source