Progress Hybrid - Shielded Cooktop and screen - diff stove

[Waulie]

Well, I guess Slow1 doesn't fit the heat sink theory. I've been running 24/7 with twice a day loads for a couple months (with the occasional break in warmer temps). You are right that loading on coals with a warm stove really extends the burn time. Once I get rolling 24/7 I just always seems to have a nice coal bed and I'm usually engaging the cat in less than 10 minutes after a reload. Occasionally, I'll open the draft to burn the coals down some because I've got too many.

It is just strange that you don't have coals after 12 hours unless you stuff the stove. Maybe when you're around all day, try several really small consective loads (small enough that it won't overheat your house) to build up a nice coal bed. Then try loading about 60 or 70% for the night on that coal bed and see what happens.

 

[fire_man]

I was trying to apply some familiar principles to figure out this burn time thing. (Thermodynamics has been a while for me too!)

To figure out a transistor's junction temperature (similar I figure to a stove's internal temperature) you multiply the power dissipated by the transistor times the total thermal resistance from junction to ambient, then just add the ambient temp. This gives the junction temp for a given outside ambient temp.

I figure a stove has a certain BTU's (similar to Power Dissipation), the house a certain R value (similar to thermal resistance), all at some outside temp. Now I just have to make sense out of it and figure out how to get to burn time??

 

[Waulie]

Good luck.

I mean it does make sense. More heat loss from the house = more gradient between the stove and the house = more heat loss from the stove = shorter burn times. Maybe there should be a differential equation in there somewhere.

 

[Machria]

How many average size splits (I know that is a very loose size!) are you guys loading when you say Full load, vs 50 or 60% load?

The whole burn time VS size of house or outside temp thing perplexes me as well. I don't see how the size of the home or temp would affect how or how long the same wood would burn in the same stove with the same draft settings. The stove has a specific amount of air and wood to use to burn, and why would it care or matter how big the space around it is? I understand it needs to transfer the heat, and would do so more in a larger area and/or lower temps, ... but, why or how would the stove "change" it's burn time based on that? It just seems it would burn the wood the same regardless of how much heat the house is taking in. The firebox is 500 to 1000 degree's, so the affect on 10 or 20 degree differences outside the stove doesn't mathmatically seem to want to make a difference on it's performance?

Disclosure: I'm not making any claims or arguments here, as I have no clue about any of this really. Just kinda talking out loud about it!

 

[Waulie]

It's cool, Machria. We're just talking out load too trying to figure out why some have different experiences than others. There likely is a bit of difference based on house heat loss but in reality I don't think it would make a huge difference. Really, Slow1 is the only one who's burn times I find perplexing. He doesn't seem to need a ton of heat but still isn't getting great burn times. Everyone else who's getting shorter burn times has huge, poorly insulated, and/or drafty houses that need a LOT of heat.

As for number of splits, I could only guess right now as I'm not home and I don't tend to count. I would say a typical 60 to 70% load for me consists of 2 or 3 large splits, and maybe 3 or 4 smaller splits and/or small rounds. I'll take a picture of my load tonight and post it. My load tonight is going to be a bit bigger since we're suppose to get 50+ mph gusts tonight.

 

[HollowHill]

I think another thing to factor in here, somewhere, is the hybrid technology. By that I mean, the temp when it switches from secondary to cat and back. I have been mulling this over with regards to the shielded cooktop. I'm figuring that the shield is "sending" the heat back down into the firebox, thus increasing the temp of the firebox, thus affecting the secondary/cat paradigm somewhat. Further hypothesizing, I'm wondering if the cooler house temps mean that the firebox is losing/dissipating heat faster and again, thus affecting the secondary/cat paradigm. I know, I haven't got this all thought out yet, just swirling it around in my brain.

 

[Machria]

I need a beer!

 

[HollowHill]

I've obviously already had one... or more

 

[Huntindog1]

First let me say I a dont have a Progress Hybrid.

I think there are several variables involved.

The flue is the main driver in the air thru the stove. If all you guys flues are different with different draws then air flow thru the stove at lets say 1/4 ways open is all different. It doesnt matter if all you are set at 1/4 ways the air flow thru the stove will be different.

Installing a Manual Pipe Damper and just like a small 1/4 way adjustment in the flue draw may make a world of difference.

Wood Quality is a big one, seems like moisture plays a lot bigger factor in burn times than people think. Add to that types of wood and wood size plus how wood is loaded. How much air space in between splits. How big and hot of coal bed did you load on.

Outside temperature will factor into how much draw of the flue as temperature difference from the bottom of the flue to the top of the flue factors into flue draw.

From my own experience with stoves and not a Progress Hybrid , someone mentioned above that loading on a good bed of coals makes for longer burn times as I think this gets you a fast heat up of the stove which leads to a quicker shut down of the air. This whole quicker start up leads to not getting all your wood burning quickly before getting the stove shut down to a low burn rate. Thats why really dry wood is so good for long burn time as it will fire up and get stove hot really quick. Big pieces that are really dry will out gas at its surface to help heat the stove up really quick on a big bed of coals but these dry big pieces will burn for a longer period of time. With really dry wood and big hot bed of coals start up is so much quicker. less of your wood is burnt up and the really dry wood has very little moisture that counters all this by cooling the fire box.

I have had really fast startup on a good bed of coals that the wood in there doesnt look like its burnt but it is out gasing and the gases are burnng up away from the wood in the top of the stove, or in your case it would be burning up thru the cat also.

If your letting your stove heat up too hot before shutting the air back down will lead to faster burning and short burn times. Seems like wood with moisture leads to longer startups and leaving the air open longer this leads to alot of wood burning and very little heating of the firebox. As your boiling water which is taking away from the heat building in the stove, then you have wood that has burned up much more before you get the stove shut down for the long nights burn. This wood that was charred much more will not last very long.

So basically if every is having different start ups and air shut downs will get different results.

 

[fire_man]

If you run a blower with a stove the fuel will burn down faster. When I ran a fan over my VC Resolute I could burn down a load in a couple hours. I figure it's the same thing but to a much lesser extent with a poorly insulated or oversized house - the heat gets removed from the stove faster and burns down the fuel faster.

Waulie I though when you said you were loading 60% full you meant that you fill up the box with 16" splits, but it could hold 22" splits. Sounds like you load even less than I thought.

 

[Huntindog1]

Fireman,

So running the blower is like having a stove in a big over sized drafty house both looks to cause wood to burn faster for some reason.

Wonder why?

Does cooling the stove at a faster rate increase flue draw thus air flow thru the stove is more, causing wood to burn faster. As temperature differences will effect the dynamics.

Wonder what the temperature difference from the center of the fire box to the surface of the stove does to the burn rate if anything?

 

[Machria]

Installing a Manual Pipe Damper and just like a small 1/4 way adjustment in the flue draw may make a world of difference.

Speaking of flue dampers, I'm installing my stove tomorrow and have been thinking about the stove pipe from stove to chimney connector box which will be about 38" up from top of stove. Should I be installing a key type damper in that pipe just in case I need/want the extra control? And if so, where should I puit it, at the top just before the connector box into ceiling OR on the bottom at the stove? And is there any particulr/special/better kind of damper to use?

 

[raybonz]

I see no difference in burn time perhaps Tony's fan was blowing towards the air intake increasing the air entering the firebox? Otherwise this makes no sense to me..

Ray

 

[Slow1]

As for number of splits, I could only guess right now as I'm not home and I don't tend to count. I would say a typical 60 to 70% load for me consists of 2 or 3 large splits, and maybe 3 or 4 smaller splits and/or small rounds.

Here then is something that I think may be a difference. If I'm reading this right you are loading 5-7 splits in your 60-70% load. I think I'm more in the 7-10 total splits for that sort of load. I think a full load could take 12-15 splits of the size I'm using right now (and that is all 15-17" loaded parallel). I don't know if this is enough of a difference to account for significant burn time differences but... I have been putting some larger splits to the side so I can try a load (on coals) of just larger splits and see what happens.

 

[fire_man]

I see no difference in burn time perhaps Tony's fan was blowing towards the air intake increasing the air entering the firebox? Otherwise this makes no sense to me..

Ray

Ray you may have a point. The VC Resolute had a bimetalic thermostat - cooling the stove by blowing air on it opened up the thermostat.

 

[Waulie]

Yeah, when I say 60% full I mean 60% full height wise with 16 to 17" splits. So, I'm really only using less than half of the total volume.

I do use big splits. I just measured and my big splits seem to vary around 7 to 8" wide on the long end. A lot of those are actually pretty square so there is a lot of wood in each one. I pretty much always put two or three of those in a load, always one on the bottom back and usually another right on top of that one making a wall of nearly solid wood. I've had several that will only fit through the door turned a certain way which I admit might be a pushing it a bit.

 

[Waulie]

Lots of people with different types of stoves have reported shorter burn times using the fan. IDK myself as the one stove I had with a fan just plain had short burns. It is reported quite a bit though.

 

[fire_man]

Waulie's giant split size (7-8" width) is the biggest single variable I have noticed that might help account for his long pure cat burns and longer general burn times. My splits are more like splinters - I got carried away with my new log splitter and over did it.

I can't wait to try the 22" long Beech that was split "Waulie size" last year. Its just not cold enough yet!

 

[Slow1]

I just did some measuring and most of my wedges are 4-5" on long side(base) and 3-3.5" high (think triangle here). I have some rectangular splits but most are 3-4" max on a side with many having 2-3" on at least one dimension. I have one 'monster' split that is rectangular 4"x8" that I will look forward to burning one cold night this week... Anyway, I am thinking the smaller split size may well be seriously contributing to my faster burns.

 

[fire_man]

I've also noticed in pictures of Dennis's stacks (and from holding actual Dennis wood) that his splits are very big, too - and he gets some excellent burn times from what I remember in his posts.

One thing I notice is my secondaries fire pretty quickly after loading, probably because of more outgassing in smaller splits. Both Waulie and Ciccio have reported long cat pure cat burns, and they both have bigger splits than me. I still get some pretty good burn times, I'm not complaining, but it's worth trying some bigger splits.

 

[Waulie]

I took some pics of my coals from this morning and my load tonight. I'll try to post them soon when I catch up on the snow!

 

[Berner]

Speaking of flue dampers, I'm installing my stove tomorrow and have been thinking about the stove pipe from stove to chimney connector box which will be about 38" up from top of stove. Should I be installing a key type damper in that pipe just in case I need/want the extra control? And if so, where should I puit it, at the top just before the connector box into ceiling OR on the bottom at the stove? And is there any particulr/special/better kind of damper to use?

I too am curious about the damper. I always thought an optional stove pipe damper was only for those with excessive drafts. I'm nervous that my draft is not going to be good enough. Obviously a damper would hamper the draft even more but is that a good thing for overall heat and burn times?

 

[rideau]

I've been in Maui for three weeks. Got back home late Tuesday night. Person who was home sitting had a totally plugged cat, with predictable results. Cleaned the cat, loaded the firebox to a comfortable height with 16 inch and shorter maple uglies. lots of air space. used a supercedar as it was a cold start....within five minutes cut air in half, five more minutes engaged cat, shortly shut air completely. Home quickly went to 74 degrees in stove room (16 x 46 room). Twelve hours later too many coals to reload, stovetop over 300. Opened air for a few hours, then reloaded. Reloaded again late Wednesday night, and about 9 AM Thursday. Temp at all times above 70 in stove room, about 64 on the second floor, somewhat cooler on the third floor. Leaving at 10:30 Thursday for a few days, so reloaded when entire firebox covered about two to three inches deep with very active coals. Wood was fully engaged really quickly, cooktop split within ten minutes of loading, soapstone top temp 250 degrees, exterior reading double wall flue temp (have to install the probe!) 300 degrees...much higher than my usual 150 to 200 degrees.
My recommendation: Don't load on lots of coals. Woodstock is sending me a shield and new cooktop.
I think we should probably all use a shield for the cooktop. Cooktop is relatively thin iron, has deep flanges on the bottom, and I believe that the cast iron is easily capable of getting too hot too quickly to safely expand.

I easily, with ten minutes spent starting the fire, get a 12 plus hour fire with no further tending, air completlely closed in these cooler temps, using largish uglies...quite a few need manoeuvering to get throught the door. Toss smaller wood in also... generally well less than 50% full re volume, on average about 2/3 full in terms of height, but not at all tightly packed, but large splits. I just make sure when I split that the pieces will fit through the door. Stovetop temps may get to 420 or so(although they are usually in the 325 range) , and remain above 300 in excess of the twelve hours. Large home is comfortable. Lots of windows, curtains closed as soon as sun sets.
I find this stove very easy to use, and to regulate output. Except when deliberately burning with very small fires, get way more heat than the Fireview.

To a point mentioned above, Woodstock has tested this stove with wet wood, and found little difference in output and efficiency. Not suggesting using wet wood, just don't think that explains the vast difference in results. I think it is split size that explains differing burn times. I consider 2-3 inch splits kindling, shoulder season wood for small fires. My stove with much of that would burn hot and fast, and burn down to coals quite quickly.

I don't know if I will ever really use much 20-22 inch wood (other than rounds up to about 4-5 inches in diameter) because of the difficulty for me of loading. My large splits at 16 to 18 inches are heavy. Adding 20 % to the length may make the wood too heavy to easily load. I'm getting as much burn time, and as much heat, as I need with 16-18 inch long 8-10 inch splits. I have about 1/3 cord of dry maple split to 20-22 inch, and will see at a time of cold start if I can handle loading with it, (once the temps are really cold ) .

 

[Waulie]

I think it is mostly split size that causes the difference.

Here were my coals with a 70% (height wise) load after 12 hours. I had just raked them forward.



Here is a somewhat typical load. This one was a bit bigger than I have been running (maybe 75% height wise) since it was going to be a very windy night. Low of 28.



This was three big splits, one small split, and one small round. I could have easily fit another big split and two more small splits or rounds. This load will produce coals at least like those shown above after 12 hours. Notice how I stacked two big splits tight on top of each other in the back. Those were 7-8" wide. Also notice I had flame before I finished loading.

 

[fire_man]

Waulie thanks for posting the picture of your splits. I'd be embarrassed to post mine, you would wonder what those toothpicks were doing in my stove.

I think your and Rideau's split size vs stove performance says lots about how important the split size is for longer burns.Unfortunately I have years of smaller splits to deal with.