Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: F7JC on December 14, 2011, 07:08:03 PM
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I know their are a ton of factors with this, but I will ask anyway.... I have a Hawken 1100 and the last few weeks I load this thing hardly twice a day. Once a day if it is in the 40's and twice when its in the 30's. So far I have been pleased with the wood consumption.
The past week end we hit the 20's, couple days went by and I still loaded twice a day. The last two nights in the low twenties I have been getting 6-8 hour burn times.... Not real happy about it, I dont want to load it in the middle of the night and nobody is home in the middle of the day. I do not understand why it suddlently started sucking the wood.
My theory is because my bubble wraped, pvc sleeved pex lines are only buried 2 foot max and the ground started to freeze robbing the heat from my setup. I have also noticed the fan in the house kicked on every 15 minutes at night, maybe its the cheep plumbing or maybe its the ineffecient house. Any ideas??
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the fan kicking on that often is a little high i think. on the other hand are you sure your bubble wrapped lines are dry, could your pvc have a bad joint and be letting water in and surrounding the bubble wrap. if your lines are dry, only being burried 18 inches shouldn't affect it so much that you would go from loading twice a day to three times. what did you heat with before this stove? what were your fuel bills for a winter with your last furnace.
has something esle changed? are you sure yoru damper is operating properly and not opening too far and you are losing too much heat up the stack? there are many things that could h ave changed, you need to investigate them all. there will be more ideas come for you to consider..please do consider them all and do your best to check them all out.
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I will try to help if I can as I have basicly the same owb. First we need to know more info. What exactly are you heating? How big is it and how warm are you keeping it? What did you heat with before and how much fuel did you use in a comparable month? What kind of wood are you using and how long has it been seasoned? How deep is your water table and have you noticed any snow melt above your underground pipe. How full are you filling your owb? When the draft fan is on are you getting any visible smoke from the stack or is it just heat waves?
I am heating a 3000 sq ft house plus dhw. My boiler is a he1000 (same size as yours). I live in Michigan (cold). My underground pipe is logstor. I keep the house 73 when we are here 71 when we are not. When it is in the teens my house blower cycles probably every 15-20 minutes for about 5-7 minutes. I have a 140,000 btu water-air hx. When temps are in the teen's at night 20's during the day I have no problem going 14-16 hours before putting more wood in. I normaly put in half loads twice in 24 hrs.
As far as I am concerned, 6 hours between fills is unacceptable and should not be occuring unless you are grossly undersized for your heating demand. Without knowing anything more I would be leaning towards your undergound line's as this is where a tremendous amount of btu's can go if things are not perfect. You need to measure the temp at the line before the hx to see what your ground loss is. This however is easier said than done unless you have a temp gauge installed in the line where it enters the house. Good luck and keep us posted.
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I have a CB5036 with Thermopex install about 1 foot in the ground. My wood burning when the temps were in the 30's at night doubled when we started having consecutive nights in the single digits. I was taken back a bit by the amount of wood increase. Recently, we've had lows below zero and I typically load my unit up around 4:30pm just at dark and check it in the morning around 6:30 just before daylight. The first night our temps dropped to -12 degrees and I had my OWB about half ful. The next morning I heard my propane heater kick on, meaning my OWB was out of wood. I went outside to find the temperature down to 154 and just white ashes. That evening I loaded it full, which I hadn't done before. The low for that night was -7 degrees and the next morning I found the OWB with some wood still to burn, but mostly gone. That was nearly a 14 hour burn at a overnight low of -7 degrees burning mostly aspen with a couple of pieces of ponderosa pine.
My point of laying that out is that our stoves are probably fairly close in performance. Thermopex line is probably the difference in efficiency compared to your bubblewrapped pvc lines. I used some bubblewrap foil insulation beneath my infloor heat water pex between floors in my house and it is not a very efficient form of insulation. You can actually lay Thermopex on the ground for awhile and not loose any heat with freezing weather, unless of course it is well below zero.
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MTJAG and woodman :post:
20* earth temperatures won't bother Thermopex much at all. My stone foundation is right at about 2' thick, so I ran mine through a window to supply my heat exchangers, and the 4' of exposed line never even melts snow unless the sun shines on it. I wrapped one layer of foil backed(or faced) bubble wrap around my side arm heat exchanger and shot the temperature and it was around 115*-120*, so I added another wrap and it is still about 10* warmer than than the ambient temperature of by old basement. That stuff is better than nothing, but it's not Thermopex.
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MTJAG and woodman :post:
20* earth temperatures won't bother Thermopex much at all. My stone foundation is right at about 2' thick, so I ran mine through a window to supply my heat exchangers, and the 4' of exposed line never even melts snow unless the sun shines on it. I wrapped one layer of foil backed(or faced) bubble wrap around my side arm heat exchanger and shot the temperature and it was around 115*-120*, so I added another wrap and it is still about 10* warmer than than the ambient temperature of by old basement. That stuff is better than nothing, but it's not Thermopex.
That's a good indicator of the difference between foil backed bubble wrap and Thermopex. F7JC do you have a thermometer on your inbound OWB water pipe in the house? If so, what is the temperature variance. On my application, the temperature on the OWB at 175 is nearly the same or maybe a degree or two cooler. Woodman suggested that you message that before your HX and that is sound advise. That will quickly tell you if the problem lies in your lines. Hope this helps, cause it would drive me nuts to not be able to figure out where all your btu's are going.
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Because you mentioned your fan inside your house is coming on about every 15 minutes since the outside temp dropped, I would have to say it is your house. Like mentioned above, we need more info on your house.
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Because you mentioned your fan inside your house is coming on about every 15 minutes since the outside temp dropped, I would have to say it is your house. Like mentioned above, we need more info on your house.
:post: Everyone seems to always jump to underground lines first. While it could be the issue, it is pretty easy to test. Get a barbecue thermometer and strap it to some copper on your incoming line in the house. Chances are it will only be a couple of degrees cooler than at your boiler. If the fan wasn't coming on every 15 minutes before and it is now, then that is why you are burning more wood. That fan is drawing BTU's out of that water and sending cooler water back to the boiler, which causes your draft fans to run more, which causes you to burn more wood. What's your differential set at on your aquastat? Try lengthening it to see if makes any difference. So if it's at 5, move it to 10, or if it's at 10 move it to 15. That way you will idle a little longer between burn cycles which should save some wood theoretically.
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Of course combined underground pipe used and how well a house is insulated are the keys to determine wood use.
Thermopex and well insulated house here= 1/4 cord so far in Dec.
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Of course combined underground pipe used and how well a house is insulated are the keys to determine wood use.
Thermopex and well insulated house here= 1/4 cord so far in Dec.
Thermopex, Logstor, or any underground pipe like them is the best you can buy. Still doesn't mean F7JC's problem is that he didn't use that pipe. Could that be the problem? Absolutely. It's more likely an inefficient house problem though.
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onemore thing, i went back and re-read the original post..what are you calling a "filling" you say you were loading twice a day in the warmer weather and now you have to load three times?
when you loaded twice was it like ..twice 30 pounds of wood (example only) and now 3 times 30 pounds..how about now that it is colder you fill twice with 45 pounds?
just trying to make sure you understand that when the weather gets colder it will take more wood..most of us who are experienced with our own OWB get to know about how much wood to put in on a mild day to get us through until we want to add wood again..like, i like to add wood at 6 in the morning and 6 at night, depending on the forcast and the temp the air is when i fuel the stove is my gauge on how much wood to put in, as i am sure many folks here do teh same thing.
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Wow nice reply on this one. I am leaning on the house being the issue. The home is only 14 years old and a two story with 1200 square feet on the main, 400 on the second, and 1000 on the basement. I have a foyer about 15 feet high in the front of the home (200 square feet maybe) and catherdal ceilings (300 square feet) in the family room. I do believe alot of heat rises there. The second floor atic has about 9-10 inches of celose and the rest of the main floor is about the same, not sure whats in the family room (catherdal ceilings). Fiberglass insulation in the walls, maybe R-19. I have been keeping the house 74 degrees. As I remember I went through 1200 gallons of propane last year with my indoor wood stove running at night and weekends (at 70 degrees). I do believe the furnace kicked on frequently also.
I am heating with green oak, maybe and cherry, I load about 5 to 7 6-8 inch logs anywhere from 2-3 feet long. Wood has set pry 4 months.
As far as the pvc having a leak in the joints I really doubt it, I pitched the line toward the basement so I could see if any water leaked in, so far no wet basement.
The little snow we had this year did melt above the lines, but at night it all freezes up again.
Not sure on the damper, the fan does make some strange noises once and a while, just have to hit the door and it stops.
From the boiler to the home I loose about 3-4 degrees, the differental is factory setting at 20 degrees I do believe, kicks off at 175 and on at 155.
As far as the bubble wrap Im not sure thats the best insulator I should have choosen in my current situation, Maybe I will spray foam around it next year or save up for the good stuff.
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Two things to look at:
1) What is the difference in your heating degree days, that number should point to a related difference in wood usage. Us a 65 degree base, it simply means that at 65 outside temp your house requires no heat due to solar and internal heat. http://www.degreedays.net/ (http://www.degreedays.net/) Degree days are the correct measure of heat load, not a rough temperature.
2) You are getting frost on the ground. Is it melted above your piping and frozen everywhere else? If you are keeping frost above your line it suggests your insulation is somewhat effective. Burried 2' down is surely below the frost line? Therefore the ground temp is above 32. How long an underground run is it? Short = less heat loss. Had your ground gotten wetter due to rain? Water can pull away heat, especially flowing water.
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My underground run is 110 feet. I do notice when it rains I burn a little more wood. But not as much when It snowed and was 20 degrees out. I'm thinking about just runing the furnace with propane for a couple days, bypass the HX and let the boiler pump run and see how much I burn that way. When we hit the 20's again that it.
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1200 gallons of propane would equal about 109,800,000 btu plus any wood you burnt in your indoor unit.
lets say in mixed hardwood you have about 18,000,000 recoverable btu's in a cord. now lets say your owb is 60 percent efficient. you would recover about 10,800,000 btu per cord. you would need about 10 cords of wood for your heating season plus what ever amount of wood you burnt in your indoor stove.
most outdoor stoves i have seen (unless your unit is quite small) can achieve this number on 2 fills per 24 hours, but not knowing how much you burnt previously in your indoor stove i dont know what to say. it could be possable you may have nights that you can't get by on 2 fills. these nights in my opinion would be severly cold and windy if your house is an average insulated house.
do you know what your OWB is rated at in btus per hour and what was your propane stove rated at per hour. this may help you in knowing if your OWB is rated for what you really need. if yoru propane stove could keep your hose warm without the indoor wood stove then you have a good start in knowing how big of OWB you need. I am not quite sure how to size the OWB but perhaps some dealers here could tell us. you must remember as long as you have propane in teh tank your stove can output the max it is rated for, with the OWB its rating may not be wuite true as your fuel supply wanes as it burns. I am not sure if OWB are rated on a burn of say one hour burn of a full load of wood or a 4 hour burn, this would change the btu output. perhaps a dealer could tell us how the btu output is calculated?
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My recent heating degree days:
12/1/2011 27
12/2/2011 27
12/3/2011 29
12/4/2011 25
12/5/2011 17
12/6/2011 9
12/7/2011 12
12/8/2011 30
12/9/2011 32
12/10/2011 29
12/11/2011 39
12/12/2011 36
12/13/2011 23
12/14/2011 21
I chewed my wife out on the 12th for running the thermostat up on the 11th. She did some but the data shows a 25% bigger heating load than the 8th. I was mostly wrong again.
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Interesting.... Last year I just about burnt 2 or 2 1/2 cords in the indoor stove. If I go through 10 cords a year with my current setup I will be tickled!! My stove is 150gallons and its rated for 225,000 btu.... as for hourly btus I wouldnt have a clue, same for the indoor stove.
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Interesting.... Last year I just about burnt 2 or 2 1/2 cords in the indoor stove. If I go through 10 cords a year with my current setup I will be tickled!! My stove is 150gallons and its rated for 225,000 btu.... as for hourly btus I wouldnt have a clue, same for the indoor stove.
your ratingo f 225,000 btu should be your hourly rating..how does that comapre to the propane stove (it should be on a plate somewhere on the stove)
as for wood consumption that would be 10 cords to equal your propane gallonage plus the 2 or 2 1/2 cords you used in your indoor stove. (this is an average guess, it could be more or less one or 2 cords) and in cords i mean real cords...bush cords..what ever you call them in your area ..a cord equals 4 feet high, 4 feet wide and 8 feet long
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I have burned a cord so far, pretty pleased with that. I fill twice a day but only 3 0r 4 pieces at a time. I'm heating a 2800 square ft. farm house. I have an oil fired hot water furnance which I only run to make sure it will run. I really like my 250 Cozyburn. on my 4th winter with it and it's already paid for itself. I read somewhere that a cord of locust is equivalent in BTU's to 100 gallons of fuel oil. So when I spend all day cutting a cord of wood and heating oil is $3.82 a gallon. that's quite a savings. Think Ill keep cutting!
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Well it snowed today and out of curiosity i ripped the foam from the pipe that runs into the mechanical room only to discover water was in the pipe.... this may be an issue.
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I have burned a cord so far, pretty pleased with that. I fill twice a day but only 3 0r 4 pieces at a time. I'm heating a 2800 square ft. farm house. I have an oil fired hot water furnance which I only run to make sure it will run. I really like my 250 Cozyburn. on my 4th winter with it and it's already paid for itself. I read somewhere that a cord of locust is equivalent in BTU's to 100 gallons of fuel oil. So when I spend all day cutting a cord of wood and heating oil is $3.82 a gallon. that's quite a savings. Think Ill keep cutting!
Dont blame you there buddy.. Current price here in NH $3.49
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Well it snowed today and out of curiosity i ripped the foam from the pipe that runs into the mechanical room only to discover water was in the pipe.... this may be an issue.
May be gound water getting inside insulation rather than a leak. Water around piping will sure decrease effiecency. That would explane wood usuage increase along with heat demand in your house increasing due to colder weather. May need to replace or better insulate underground piping at some point. I would suggest running piping inside a casing like 4'' or 6' pvc to keep it dry if you insulate it yourself.
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I did run it in 4 inch pvc, must have been damaged when I backfilled it or had a bad joint. I'm thinking if trying to get away with it the rest of the year and replace it with thermapex or something similar next spring. We will see. Piping still looks moist on the bottom, yet only lossing 5-6 degrees, hopefully I can make it work the rest of the winter.
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The fact that your insulation is wet may not be as catastrophic as people imply. I guess it depends on the insulation. Closed cell foam will remain fairly effective because it doesn't hold water like a sponge. Most of what we use for PEX insulation doesn't really absorb water. Water is a good transferer of heat but a little trapped water is not a disaster. On the other hand if you have the inside and outside of our 4" pipe filled with water it would transfer the heat from the PEX quite effectively. Especially if the ground water was flowing thru the area. I think the best data is the temperature drop from OWB to House. I'd assume the return to be similar. You might check this drop at various times, especially after a good rain as compared to after you have had no rain for a period (dryer ground).
It seems most people think 3-5 degrees is a reasonable loss. I don't know what mine is and even if I had an IR Thermometre I'm not sure that shooting a metal fitting exposed to outside air (at the OWB) and then a fitting in the basement (65 F) would be accurate. Maybe if it was the same temperature outside as the basement it would be representative of heat loss. Hey, I need one of those IR tools anyway, and I now have a Lowes Christmas Gift Card :-)
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perhaps a smal amount of moisture could be condensation? also losing 3 or 5 or 5 dgrees in the ground may be a lot or not much? the heat loss in your pipes is also tied to how many GPM you are moving. lets take some imaginary numbers (only because i don't know the real ones) two house are matched perfectly in pipe size, stove size square feet ..evrything but one thing GPM. fan speed exchanger everything is the same but GPM so both houses call for heat, both are delivering 180 degree water but one is delivering 5 GPM and one is delivering 10. the house that is getting 5 is losing 10 degrees on the out (return)side of the exchanger and the house delivering 10 may only be losing 4 or 5...it would work the same in your underground piping. if you read the adverts on some of the underground pipe it will (or may) say that it has a 1 degree loss in 100 feet of pipe, also in the fine print i have seen it say ..this test was done at 5 gpm and water temp of 180 in the pipe and 54 in the ground. all three of these things can and will make a difference
if you are melting snow above your pipes ..you are losing enough heat to account for quite a lot of wood consumption. my underground pipes are 250' from the OWB to the house. i used to have a melted area 3 to 4 feet wide above them with my old insulation. last year i replaced them with the foam stuff n the black sheeting and my i have no melted area now. in my situation it saved me about 1/3 of my woood consumption! i would not have believed it until i recorded it myself.
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WillieG-
That should be pinned somewhere! Great explanation!
Bottom line=Don't go cheap on your underground pipe!
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Yes, willie is right. If I lose 1 degree F with my circulatot on high that could be much worse than 3 degrees with it on low. I have the 3 speed TACO. The temperature loss just 'represents' BTU loss but probably needs multiplied by a flow volume. But since temperature is the thing we can measure ...
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I have also noticed less noise in the pipes in the mechanical room in the last week or so. Like the flow has slowed down a bit. Purhaps i should put another pump in to see if results are similar. The water in the basement may be condisation, it really hasnt flowed out, rather a steady drip, right after a rain or snow. Also the little bit of snow we had this year has melted above the line two to three foot wide. But at night frost and any moisture freezes about the line.
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if this has been a new install recently, it may melt over the line for a bit as the ground has not settled completely ...but if it is still melting snow in the heart of winter when the air temps are not above freezing and the direct sun is not heating things any, then you can likley consider a problem