FPX Burn Times

Got Wood said:

BrowningBAR said:

I have no experience with this stove, but 4 hour burn times on a cat fireplace insert that claims 75% efficiency with a 4.3 Cubic Feet fire box would seem... very frustrating.

I love the look of the insert and was thinking about redoing the living room at some point to accommodate something like this. But, based on this thread, I think I will change my long term plans.

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I really have no regrets installing the FPX. It really is great looking, I'm dang proud of the finishing stone work I did cause I dont consider myself exceptionally handy but I got some good help and love the end result. the large fire box and viewing glass doors really are nice to view. find myself staring at it a lot. And it does kick out a great amount of heat. I would say it provides 98% of the heat for the house with the exception being those brutally cold winter mornings when the furnance kicks on for a short time before I get it blasting heat again. The POS system does work too - I have some older drafty windows and when the fan is running there is no draft. It circulates the heat through my house nicely too. So, its great looking (a real center piece to the room) and provides all the heat for the house.

The burn time length has been frustrating but only because I hear about these 10-12 burn times on this forum. I have never used any other wood burning unit for primary heat so I dont have any comparison point. The unit does fall short of advertised lengths but my guess is most do too. With the shorter burn lengths I probably use more wood than those with other units (Last winter I used 5.5 cords). The burn length isnt a big issue for me as I work from a home office and as a family we prefer cooler sleeping temps and dont mind waking up to a cooler house.

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I am in the same boat as you I love the unit and can't beat the looks of it.

It's just my nature to try and improve things and right now this stove is a challange and i enjoy it. I would not be unhappy with any improvements but at the current moment I am content with it's performance.

It's located in the family room
My house has a very open floor plan so it helps

All the above on good bed of coals...I stuff as much wood as I can in the 36, maybe 4-6 splits of Almond, then I'm usually good for 6-7 hrs. of a good overnight burn and residual coals in the morning. The fan is sometimes going intermittently off/on when I get up at 6am, so I know it's still warm, but a few more splits on the coals then it takes off again. I keep the fan on about 3/4 and the air just barely open, if the air is closed all the way then I'll some black.

What kind of wood, and how full or how much do you put in the the box?

I try and arrange so it's pretty compact. With 3-4 splits, I'll get 6 hrs.

MDfireguy said:

FPX Dude said:

I try and arrange so it's pretty compact. With 3-4 splits, I'll get 6 hrs.

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yep, I packed it tighly last night and it was still going good at 6 hours. Thats much better. I was afraid to pack it tightly in fear that the wood would smolder and not get enough oxygen. It's sort of like burning a solid wood brick...but it worked.

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Interesting, you back 50% more burn time by packing the same amount of wood tightly. Do I have this right? Also, I assume that is on a good bed of coals to start out with?

I have been most successful with smaller splits and build them like a block tower in the box. Always go the whole burn cycle. 6-7 Hours tops though on coals. Unit always warm to touch though in the AM. Usually I need to relight (rebuild).

This video demonstrates it well http://www.woodheat.org/images/Video/StoveOp.wmv


As an aside-

I have a friend with a soapstone and a slightly larger house than mine. Room config is very similar. The soapstone does not warm the house as much as the FPX (with blower running). I think in the larger homes the posi-pressure really works.

That said- it definitely likes to gobble wood.

Mdfire how many splits are you putting in when you pack it tightly?

I pack it tight with large splits over really hot coals at 10 and the blower is still running at 6. Im able to reload at 6 with smaller splits over warm coals and get a roaring fire in 15 minutes. When i get home from work i reload with small splits again over warm coals . I dont use posi pressure exterior air supply.I was afraid of smoke smell in the house. The glass is very dirty with the low setting. I clean it with a razor blade scraper and never use any cleaner or towles. I clean the glass just so i can see that cat is working.

I too have had success by packing the wood tighter. Personally I am terrified of overfiring the stove since you can see what is going on behind the wall. The manual states to look for glowing behind the face plate (not the cat but on the actual frame). I don't think I have come close. Bought a $20 magnetic and affixed on door just under the cat damper rod. Highest reading I got was about 300F (again on door). Packing tightly, burning hot good wood has just about eliminated the black glass even with the air control all the way closed down. Just a haze that really isn't too bad to wipe off.

Typically load around 10PM. Reload around 6:30AM. Some coals in the bottom. Haven't used a match in over a week. Wife loads during day and but runs it cooler.

Hi, I am Derek. I am new to the forum although I have been lurking for a while. This is my first year burning and I have an FPX 36. My wood supply is ok but not ideal. I scored 3 cords of wild cherry that had been down for 2 years. I cut split and stacked this in late June of this year. I also scored 3 cords of hard wood from tops that were left over from logging a woods 4 years ago. I cut split and stacked this in late September of this year. The cherry is very dry but the rest is not seasoned very well. I am getting 5 - 6 hours of good usefull heat per load and have enough coals to relight the next load 10 to 12 hours later. Right or Wrong, here is how I operate the stove and look forward to any advice. I always load the box full although I do not arrange and stack the wood so that it is as tight as I can get it. I have been mixing the wood by using 2 - 3 good sized splits of the not very well seasoned wood on the bottom of the load and filling the rest of the box with the cherry. My splits are 20" long but I have some shorter ones I use for the back of the box. I have removed the grate from the box and prefer to leave some ashes on the bottom. I light the load and run full air and bypass full open until the combustor temp gauge (purchased from Condar) reads 700. My fan usually kicks on before this point when the stove top guauge (also purchased from Condar and placed on the top of the door) reads 200. I then close the bypass, leave the air wide open and watch the combustor temp gauge climb to 1000 - 1200 degrees. At this point I throttle the air down to maintain combustor temp in the 900 - 1100 degree range. I then wait until all splits are glowing red and most of the flames have died down. At this point I clse the air completely down and let the FPX do its thing. The stove top gauge never gets above 350 and progressivley drops after the air is closed off. The fan (which I always leave on high) will run for about 5 - 6 hours. My overnight burn and durning the day burns always leave enough coals 10 - 12 hours later that can be recovered with a coal shovel and placed in the front of the box to start the next load. My glass stays clean now. However, if I shut the air all the way down too early it will coat my glass with a nice layer of creosote. If I leave the air open (even just slightly) for the entire burn I will only get about 3 hours of usefull heat from the load and no coals at all left in 4 - 6 hours. I am extremely happy with this unit. If anyone has any suggestions on how I can improve my process my ears are open. I have a 1900 sf ranch (open floor plan) and another 1900 sf in the basement. We have been easily able to heat the house with the FPX and have not used any other form of heat yet. The house we keep in the 72-74 degree range on the first floor and the basement (unfinished) stays 64 degrees. I have the air intake blower for the FPX mounted in the ceiling of my basement which draws its air from inside the basement as I did not want the positive pressure setup. I also installed a return air vent for our furnace in the ceiling of the family room (this is where the fireplace is located). We have a circulation mode on the furnace which turns the fan only on for about 10 minutes every 30 minutes. This does a nice job of balancing the temperature in the house. However, it is still always a little warmer in the family room than in the bedrooms. It has never been below 67 in the house after an overnight burn but usually around 70 and sometimes we have to turn the fan on the fireplace off for a while 2-3 hours into a burn if the house reaches 78 degrees. Our chimney is on the outside of the house but I insulated the exterior walls of it and did not insulate the wall between the chimney and the family room. The chimncy pipe runs straight up with no elbows 19 feet. The outside air vents are coiled to prevent too much air from blowing through. I was hoping for longer burn times but based on others comments It looks like its not going to get any better. I am hopeful to get my wood supply built up so that I am only burning seasoned wood as I am concerned about creosote build up in my chimney. I will definately clean it after this winter. Sorry for the long post and thanks for all the information you guys put on this site.

MDFireguy, my wood is not completely coaled when I shut it all the way down. It is still in log form but glowing red hot. The flames are not completely dead at this point either but the show for all practical purposes is over. This happens about 2 hours into the burn. It is a pain if you want to light quickly and leave. If I have to leave before the wood hits this stage I leave the air cracked open slightly. But my best results happen when I can choke that air completely off about 2 hours in. I hear you on the quality of wood thing. I hope to have all of next years wood ready by spring and then get 2 years ahead and stay there. I know that better seasoned wood will produce better results with this thing.

Does anyone get backpuffing when you close move the lever all the way closed? I was thinking of drilling some holes in the air assembly plate. The reason i want to do this is get my wife to reload when im not around. Just easier for me to instruct her to load it, wait till it gets hot then close the bypass and put the lever all the way to the right.

hughmyster, I don't have any trouble with "backpuffing" at all. I do however always open the air control and damper all the way before opening the doors. I also open the doors slowly. The only time I have ever had smoke roll back into the house is when the doors were opened quickly. The movement of the doors creates a draft stronger than the draft from the chimney for a brief second allowing the smoke to roll out of the box. I really don't think drilling holes in the plate is going to help much with this matter. And the downside would be that you would lose the ability to choke down the fire for a long burn or to get it back under control if it started to climb to extremely hight temps. I could be wrong but I would strongly advise against that plan. It is my understanding that backpuffing with a hot stove would almost have to be caused by negative pressure in the house (assujing the chimney isnt' clogged). Try opening the window closest to the insert for a minute before you open the doors and see if that solves the problem. In new construction homes that are built air tight it doesn't take much to cause negative pressure. Exhaust vents like the ones above your oven and in the bathrooms are enough to create this negative pressure situation.

Derek said:

hughmyster, I don't have any trouble with "backpuffing" at all. I do however always open the air control and damper all the way before opening the doors. I also open the doors slowly. The only time I have ever had smoke roll back into the house is when the doors were opened quickly. The movement of the doors creates a draft stronger than the draft from the chimney for a brief second allowing the smoke to roll out of the box. I really don't think drilling holes in the plate is going to help much with this matter. And the downside would be that you would lose the ability to choke down the fire for a long burn or to get it back under control if it started to climb to extremely hight temps. I could be wrong but I would strongly advise against that plan. It is my understanding that backpuffing with a hot stove would almost have to be caused by negative pressure in the house (assujing the chimney isnt' clogged). Try opening the window closest to the insert for a minute before you open the doors and see if that solves the problem. In new construction homes that are built air tight it doesn't take much to cause negative pressure. Exhaust vents like the ones above your oven and in the bathrooms are enough to create this negative pressure situation.

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I also open the doors slowly when reloading. When i say backpuffing i mean when i close the air control all the way down the wood gasifies and have mini explosions causing smoke to be pushed out the door seals. My chimney is 30 feet tall. The smaller the splits the more backpuffing i get. Does anyone else see this?

Sidebar, where do you guys put the thermometer on the FPX? I dont like putting it on the doors, dont think that is accurate. I thought about pulling hte face plate off and putting it on the top of the stove that way, but assumed that the air blowing over it would screw up the readings.

Never found a good spot.

I would strongly recommend against drilling holes. These units are UL/FM approved and tested as designed. Some thought goes into the holes and how much air the box has for combustion. Drilling holes would be like leaving the door cracking....I think this would be a surefire path to something very bad.