Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: concordprof on January 19, 2014, 07:35:49 AM
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First, I would like to say how useful this forum has been to me over the past few weeks. I read the forum everyday and learn so much. However, I am at a breaking point with my NEW (10/13) CB 4030. I apologize for the lengthy post. I just want to provide as much info as I can. The specs are as follows:
-2000 ft new construction
-Full basement that is not currently hooked to the owb (would like to if possible)
-Water to air heat exchanger on a 3.5 ton hvac system
-My stove is 45' from my house. The line comes into my basement, over about 20', up to my attic, and over another 30ft. All of the 1" pex is insulated with pipe insulation. There are ten 90s total on the entire run with the required thermostatic valve. I think the heat exchanger is the cb 125k btu.
The current pump is this one: http://www.amazon.com/Taco-009-F5-Single-Phase-Circulating/dp/B000LDFNAS (http://www.amazon.com/Taco-009-F5-Single-Phase-Circulating/dp/B000LDFNAS)
My wood situation is mostly seasoned oak, hickory, and maple. However the majority of it is wet due to laying in the weather before I have a chance to buck it. Once it's cut, I store it under black plastic.
I live in southern wv so the winters are average. Last night it was 20 degrees and that is average for this time of year.
Here's the problem:
I am only averaging 8 hours of burn time when it drops below 40 degrees. I have probably already burnt 12 cords of firewood since the end of October. I know the it is hard on the owb when the water temp drops below 150 but that is occurring everyday on mine (happens over night). Usually I put 3 logs in it at 4:00, put a few more in at 7:00, and then have to stay up and fill it up at 11:00 in hopes to heat my home overnight. I spend probably 60-80 minutes per day out there. After reading this board, I have came up with the following possibilities to help mitigate this problem:
-dry seasoned wood will make a huge difference
-look at changing the pumps out
-water storage tank in my basement
- add a few chunks of coal
-sell my 4030 (anyone know what they are going for used?) and purchase either the 5036 or another brand that is rated for homes larger than mine
- any other suggestions you all might have?
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Welcome to the board! Sorry for all of your troubles. I think you should be able to heat 2000 sqft that is properly insulated just fine with 12 hour+ burns. I suspect that you may have a Delta T problem possibly. Could you do us a favor and measure the temperature of the pex when it leaves the OWB and returns to the OWB as well as the temp when it enters the water to air HX and when it exits. I am going to suspect that the forced hot air blower in the house runs ALOT. What are your temps leaving the air registers in the house? The best way to take the temps of the pex and the registers is with an IR gun which can be picked up at any big box store for around $40, they are worth their weight in gold. Wet wood isn't the best to burn and you lose about 30% efficiency with it but if you burned 30% less than 12 cords that would be about 8 cords burned so far which is WAY to much still. We will know if your pump needs to be changed after you give us the temp measurements. You probably don't need to go the extra thermal mass storage route(people don't like that route around here either except Sprinter and I). You don't need any coal to to extend your burn times, you should be able to do 12 on wood without an issue. Get us those temp readings and I think we will be able to find your problem right away.
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You probably don't need to go the extra thermal mass storage route(people don't like that route around here either except Sprinter and I).
Just because others don't like it, doesn't mean its an avenue that shouldn't be explored. I've posted enuff good design and sizing info for doing a complete system start to finish and full troubleshooting. Short of spoon feeding everyone info, it helps a person understand better when they learn it themselves. It also eliminates confusing opinions. A lot of these systems do work , but are far from correct or efficient. Not many installs going in on the design day temps. So these problems arise as soon as the system is put to the test.
Unfortunately to remedy, it usually means more money.
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Hondaracer
You are correct about how often the fan runs on the air handler. I bought a cheap infrared to check the temp and this is what I found.
Thermostat reads 180
Ir temp of pump 180
Ir temp of pex (out) at the owb 153 (I know this isn't right)
Ir temp of pex (in) at the owb 133 (while not accurate, there is a 20 degree difference?)
Ir temp of pex (in) at the hx 147
Ir temp of pex (out) at the hx 143
Sprinter
I've read a little that has been discussed on here about mass storage but don't want to out a ton of money into it. Would an old 80 gallon water heater work? Would it even be worth it?
I'm still considering selling after winter and going a size bigger, but would like the current 4030 to work if possible.
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While I dont know much about Water to air HX, the 140-150 dont seem high enough from what I have read on posts.
Sprinter might have a better answer, but thought that they need temps closer to 170-180 with dT of no more that 20
Sorry couldn't help, I run in-slab so my temperatures for operating are way LOWER
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I don't know how much I trust the IR temp gauges for reading pex line temps. What I've found with my IR is that the surface you are aiming the thing at makes a huge difference in the reading. For example, the exhaust stack on my oil burner is partly galvanized and partly a flat black pipe. With the burner running I can get a temp of 110 degrees on the glavanized portion while one foot from it on the black pipe I'll get 160 degrees. When I lay the IR gun right on the pex line, I can get a difference of as much as 20 degrees just by slightly moving the IR gun around, all the while holding it directly on the pex.
I think the 20 degree difference that you're seeing between the OWB 'out' and 'in' lines is a good thing. From what I've read here, 20 degrees is a good differential temperature between feed and return lines.
As for my OWB, I have a Hawken, and because they pull the water off the bottom of the boiler, I get roughly a 165 degree reading at the metal outlet right at the back of the tank. I say 'roughly' because I'm using the IR gun and the fittings before the pump are painted a semi-glossy black color. One foot down the line, right after the pump and on the pex line, I'll get a 155 degree reading. There is NO way I'm losing 10 degrees in one foot!
Assuming the 165 degree reading is correct, which I assume is close because the boiler is set to shut off at 180 and the aquastat is at the top of the tank, I am getting adequate heat for the water to air heat exchanger in the building with forced hot air heat. It will only heat the building to 65 degrees when it is 0 degrees outside with a stiff wind, but the oil system wouldn't even do that much, so I'm happy with that.
The other outlet on the OWB feeds the main house, a 12 room, uninsulated old house that has hat water baseboard heat. The OWB runs a LOT to keep up with it, but it maintains the old oil boiler at 150 degrees even when all the zones, (6), are calling for heat. So again, I'm happy with that.
I'll add that the main house is 230 feet from the OWB and the other building is 137 feet. And both systems have a TON of 90 degree elbows on the pex lines because of space limitations.
My point is that I *think* 160-ish degrees of OWB water should be enough to heat what needs to be heated as long as the original heat system is sized correctly too. That's the problem in the first building I described; the forced hot air oil system isn't big enough to move enough air to heat the space we need to heat in the first place, so I'm not sure how the OWB is doing it!
My other point, (if I actually have one!), is not to trust the IR temperature guns. I think they're fine for rough readings, and maybe a $300 unit would be more precise, but the $50 ones like I have are not all that accurate. I'd like to get something with a probe that I can actually lay on a pipe and get a good reading.
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The IR guns can be finicky to get an accurate number with. I have found mine to be very accurate if you do three things. One is measure the pex where it has been covered with pipe insulation(I peel back some insulation and then take a reading). Two is hold the gun in line with the pipe and three is hold the gun sensor right on the pipe. My readings with mine are very accurate if I do that. The temps through the water to air hx are not correct or you are losing alot of heat from the OWB to the house and from the house back to the owb. That looks like you are losing 5 degrees from the boiler to the house and 10 from the house back to the boiler excluding what the heat exchanger is extracting from the water which is for some reason WAY to low. It should be extracting around 20 degrees from the heat exchanger. It could be that your pump is moving water VERY fast and the delta t is just not very much but I highly doubt that. I suspect you may either have a large air bubble in the hx or your fan in your forced hot air system is moving very little air across the heat exchanger. What are your temps coming from the registers in the house? Any way that you can gain access to the heat exchanger so that you fan feel or measure temps on it to make sure that it has the same temperature in every area of the unit?
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Great post Honda, I'll add one thing, the heat exchanger may be getting plugged up on the hot air side with dust and hair reducing air flow through the rad, that's the first thing I would check. Air filter?
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Thanks Slim, I hadn't thought about the hx being plugged with dust. I was thinking about what else could cause the blower to not move enough air across the hx to extract the temp and I was wondering if you have a multi speed blower? Could it be set to only spin up on a lower setting possibly? This doesn't explain why your blowing through so much wood( I am wondering about temp loss in your underground piping). What do you have for piping in the ground?
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That's the beauty of the forum Honda, soooo many people and ideas, nobody can think of everything nor has the time.
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Does the 2000 SF include the basement? If not that is a lot of area to heat.
How is the house insulated? Could you be loosing that much heat?
What type of underground pipe? 147-153? 6 degrees seems like a lot to me and may be the problem. If the underground lines get wet they loose a lot.
Is your wood split or whole rounds. Even wet, it should do ok but will use more. I find the whole rounds seem to last longer, but split dries better. You could try different sizes and see if there is a difference.
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The IR guns can be finicky to get an accurate number with. I have found mine to be very accurate if you do three things. One is measure the pex where it has been covered with pipe insulation(I peel back some insulation and then take a reading). Two is hold the gun in line with the pipe and three is hold the gun sensor right on the pipe. My readings with mine are very accurate if I do that. The temps through the water to air hx are not correct or you are losing alot of heat from the OWB to the house and from the house back to the owb. That looks like you are losing 5 degrees from the boiler to the house and 10 from the house back to the boiler excluding what the heat exchanger is extracting from the water which is for some reason WAY to low. It should be extracting around 20 degrees from the heat exchanger. It could be that your pump is moving water VERY fast and the delta t is just not very much but I highly doubt that. I suspect you may either have a large air bubble in the hx or your fan in your forced hot air system is moving very little air across the heat exchanger. What are your temps coming from the registers in the house? Any way that you can gain access to the heat exchanger so that you fan feel or measure temps on it to make sure that it has the same temperature in every area of the unit?
"Hold the gun in line with the pipe" What exactly do you mean? aim it at the pipe or aim it along the pipe?? I've had trouble getting readings that make sense.
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Hold the gun parallel with the pipe and put the opening for the sensor right onto the pipe. Te sensor sits back in the housing of the gun about a quarter inch so your not actually touching the sensor to the pipe or anything. This just ensures that the sensor isn't reading any other surfaces other than the pipe.
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Could there be a problem with the insulation on the boiler itself? I see people commenting that they don't like spray foam insulation because it can crack, etc (I have no experience either way as I just put a down payment on my first owb) so that popped into my mind about your situation. Maybe it's cracked in places, or parts have fallen off, and you're losing heat before it gets pumped into the house?
If you're needing a new boiler, order one soon or you'll have to pay tons more in 2015 for a gasser.
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Concord,
We live in comparable climates (Lowest temp this year has be 12 degrees so far.
We both have conventional style boilers. My setup has a much smaller firebox and I'm able
to heat my 2,500+/- sqft block house no problem.
I normally buy seasoned wood and leave it out in the elements 1- 2 years before I cut & split.
I've left wood on my truck and forget to stack under a shelter a few times. It has been wet
from rain and not caused to much of a problem.
Based on the specs of your stove compared to mine I believe it should keep up.
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Hopefully he'll be able to take a look at his heat exchanger and figure out why he is only extracting 5 degrees off the water when it goes through the hx.
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Sorry guys for not replying sooner. I appreciate all of the comments and I will try to answer the questions.
I didn't think the numbers were correct but I figured the temp difference was what was needed. What should be the difference between the out and in at the owb? We just had a cold front come through. I've been burning seasoned locust and it has improved my burn times some, but I'm still not getting more than 10 hours when the temperature is below 35 degrees.
I am going to try to follow Hondas recommendation and try to get a more accurate reading. It would be difficult to take the hx out so I would rather not try that.
How would I go about checking for the air bubble?
Regarding the filters...I change those about every month.
I have their thermopex buried about 20" deep. The dirt has settled so water lays in the ditch at times (new construction so no grass seed planted there yet).
Linda...The 2000 ft does not include the basement but I would like to add that in the future only turning the unit on when I'm down there.
If I sell, what do used (1 year old) units usually sell for? Brand new before taxes is $5000.
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I don't think I would sell.
Your firebox is much larger than mine, you should (On Paper) be able to transfer heat faster than mine.
Sounds like you may start looking at the water laying in your ditch.
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Yea the problem isn't the stove at all. Your numbers are telling us that you have some issues there. Please retry your readings to make sure that they are accurate. You should not be losing that amount of heat from the boiler to the house and from the house back to the boiler. You also need to extract more than 5 degrees through the heat exchanger. Something may be wrong there such as an air bubble. If you could find some way to get access to the hx(not pull it out but atleast be able to either put your hand on it or shoot the IR sensor towards it to make sure that you have heat all the way around it. What are your temps coming out of your heat registers in the house? You said the fan runs all of the time. That is because you are extracting so little heat from the piping that you likely only have mild temps coming from the registers. I get around 135-150 coming from my registers.