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[Jd79]

I built my OWB in 2014 (can see the build if you search under homemade and look for post under my userID).  I have used it for the past two winters, and have fired it up for this season already.  I am at my wits end trying to figure out my wood consumption.  The OWB heats the house and DHW fine, but it seems like I am going through ridiculous amounts of wood to do it.  Here's my setup:  Approximately 175' of 1" pex-al-pex to the middle of the crawlspace where it transitions to 1" regular pex, goes to the 30 plate at the water heater, then to my coil, then back to the crawlspace where it transitions back to 1" pex-al-pex to head back to the boiler.  Total round trip is approximately 400'.  I spray foamed it in the trench.  I'm wondering if this is my problem?  I noticed last year that there was SOME snow melt by my boiler and near where the pipe enters the house, but I didn't think it was TOO significant.  Pipe averages about 30" deep for the majority of the trip through the yard.   My Maverick temp indications show 7 degrees difference round trip when nothing is calling for heat.  Both are strapped to the piping at the boiler (supply and return).  I don't have any in-line temp gauges.  I'm heating 1800 sf of decently insulated home (built in '04) and DHW.  We use a lot of hot water, and for some reason our incoming water line is extremely cold in the winter time.  I have seen it pull the return temp down 40 degrees when we are running both showers.  If the heat kicks on, it will drop it a little more.  This tells me I am not moving the water fast enough, but I figured a TACO 0013 would have been enough when I did my initial head loss calculations.  Things I have tried:  adjusting amount of air flow, adding fire brick to bottom of firebox, using seasoned wood only, using green wood only, using a mix of wood, thrown in a little coal, played with increasing and decreasing my differential setpoints for when the blower kicks on and off (currently set at 12 differential--168 on, 180 off.)  Nothing has made an appreciable change in wood consumption.  I also placed a scrap piece of 1/4" steel in front of the chimney in the firebox so the flames won't blow up the stack.  Instead, they hit the plate, roll up and around the tank, then go down and exhaust up the stack to conserve some of the heat.

When I load the furnace, in milder weather like now (typically upper 30s and lower 40s) I can fill it 2/3 full and it will last 11-12 hours.  Last night it dropped to upper 20s.  I loaded it 2/3 full at 7:30 and at 3:45 am my alarm was going off for low temp (out of wood).  There was a heavy frost on the ground this morning, but none of it was melted over the lines.  To get an idea of how much I am loading, I am putting about 10 pieces in, approximately 18-24" in length and anywhere from large splits to whole 6" round un-split logs.  When it gets to teens and especially single digits, I can fill this thing up full and get 8 hours of it.  My back can't take this much longer!  A rick (4x8 face cord) lasts me about 3 to 3 1/2 days in the middle of winter.

Is my furnace undersized?  Are my lines junk?  What am I doing wrong? 

[RSI]

How much regular 1" pex do you have in the system?
Is the crawl space insulated? If not, is the pex-al-pex insulated?

[hondaracer2oo4]

Your lines are junk is my vote. We can figure that out though pretty easy. My maverick is reads two different temps between the two different probes. I would confirm that yours is accurate. If you are right that you are losing seven degrees with no call for heat that is pretty significant depending on how many gpm you are moving. If you are only moving 5 gpm and losing 7 degrees over 400 feet that isn't terrible. If your boiler holds 200 gallons and you lose 7 degrees every 40 mins that isn't terrible but not great either. If you are moving 15 gallons per min and loosing 7 well that's bad. How many sqft you heating? Your pump may be to small but the btus you have created have to be dispersed somewhere. I had foam in trench lines for 4 seasons. I think they got worse and worse every season. I replaced them with logstor this year when I built my garage and what a crazy difference in idle times. My boiler use to fire every 3 hours at the longest. Now with the purge cycles and no calls for heat it can go almost 8 hours between a 160-180 run. Like I said confirm you are losing that much heat from supply to return and how mug water you are flowing.  By the way my closed cell foam was squishy with water in the couple areas I dug up.

[Jd79]

How much regular 1" pex do you have in the system?
Is the crawl space insulated? If not, is the pex-al-pex insulated?

In between the floor joists are insulated, but the block walls of the crawl space are not.  My memory may be off, but the more I think about it, I think I ordered 300' of pex-al-pex, not 350'.  I cut that length in half (one piece for supply, the other for return), laid it in the trench (lined with plastic) and spray-foamed it myself.  I know I ran short because the initial intent was to run pex-al-pex all the way to the heat exchanger, but it ran short about halfway across my crawl space, so I transitioned to 1" pex at that point because that was all that was available locally.  Nobody around here has ever heard of pex-al-pex.  I would estimate 25 feet of 1" pex from the supply side pex-al-pex connection to the heat exchangers, then another 25 feet back from the exchangers to the pex-al-pex again.  I know that flub-up added extra head loss due to decreased ID of the pipe I hadn't accounted for originally.  All pipes in crawl space have the foam pipe wrap around them (the stuff that comes in 4ft sticks and is 5/8" thick).  Hope this explanation makes sense and isn't too confusing.

[Jd79]

Hondaracer2004--holy smokes!  8 hours between cycles?  I'm not sure how often mine cycles, but I know it is a LOT more often than that.  I'm only heating 1800 sf.  Was hoping to heat my 1600 sf shop at some point, but with this wood consumption I'm not even going to try heating that old drafty building.  When I built "Woody" as my kids call it, I put a separate set of supply and return ports to put a future pump in for the shop.  My water capacity is around 200 gallons, give or take.  I used about 2/3 of a 500 gallon propane tank for the water jacket and 1/2 of a 250 gallon for the firebox.

[RSI]

Did I read it right that your return boiler water was 40 degrees? Is so, has it always done that? The 0013 pump should be able to move enough GPM. If it it didn't used to do it, I would try cleaning the plate hx.

If you have a real low flow rate then you would see a large temp drop even with no load.

Depending on how you built your boiler, a super low flow rate might have really poor circulation in the water jacket that may be part of the wood usage problem.

[Jd79]

No, I was saying that the plate exchanger will drop the temp 40 degrees when there is a demand for hot water, as in supply on maverick shows 180, return shows 140 or even 130  sometimes, especially if house is calling for heat at same time.  One time when kids were showering, dishwasher was running and washing machine was going, I remember seeing it drop to 120 with a supply of 180.

[hondaracer2oo4]

Confirm your maverick temp probes are both reading the same temps on the same pipe. If they are than your pump isn't moving enough water. But still, the btus you make have to be going somewhere. The real question is how much of a drop with no call for heat and how many gpm are you moving. If you had a flow problem in the boiler you would be boiling in some spots which would lead to having to put water in it constantly to make up for that. Yes you read that right. Around 8 hours!

[RSI]

It sounds like you have a somewhat decent flow rate. 7 degrees heat loss with no load would use a lot of wood. You need to confirm you are getting accurate readings like Hondaracer mentioned. If you aren't insulating the pipe and probe, I would do that to make sure ambient air temps aren't giving you a false reading. Also, make sure you are on the same kind of pipe on both supply and return.

[Jd79]

Will do.  My concern is that the pipes are touching some in the trench and the supply may be heating up the return on the way back to the furnace, masking some of the heat loss since both probes are at the furnace.  I have tried a laser thermometer to check temps at the house, but that thing was so far off, I couldn't get any useful data.

[hondaracer2oo4]

The ir thermometers work well if you follow a few rules. One is that the further away you are from an object the larger the area it is measuring. Ussually at a foot away it is measuring something like a 3 inch circle and taking the average of that 3 inch circle for the temp. So if you are trying to read a pipe you need to place the sensor end right on the pipe. Second thing is that if it is shiny it throws off the sensor. So wrap the area you are measuring in black electrical tape. Those two things should help you get an accurate reading. If the pipes are touching themselves in the pipe that should to be hurting your efficiency to bad either because you still wouldn't be actually losing those btus. They would still be in the boiler system.

[RSI]

Yeah, pipes touching together won't matter much and would actually give you a higher return temp.

If nothing has changed since you first had the pipes foamed then I would look at other possibilities first. If it has gotten worse, I would dig up a section of the pipe and see if it seems water logged.

[mlappin]

Yeah, pipes touching together won't matter much and would actually give you a higher return temp.

If nothing has changed since you first had the pipes foamed then I would look at other possibilities first. If it has gotten worse, I would dig up a section of the pipe and see if it seems water logged.

Unfortunately I’m leaning towards heat loss in your underground.

I made mine as well, worked very well for quite a few years, then started to notice a little snow melt at the house where they turned to head towards the OWB, then started to notice some at the boiler the next winter, the last year they were used I had a green streak for 120 feet or so from the house to the boiler, that ate a LOT of wood. Replaced with Logstor, some of that was exposed at a spot I had to hand dig to repair a drainage tile from the house, then had an ice storm, ice stuck to the Logstor until the sun melted it off.

When was the last time the plate exchangers were flushed? If they are starting to plug that will definitely cut flow. If you’ve seen huge temp difference from day one inside then for some reason the flow is too low, I ran 1” pex for years with a Grundfos 26-99 and never seen more than a 25 degree temp drop, but that was also just one water heater and a 20x20 HX in the furnace.

[Jd79]

It has always had a huge drop when there is a demand on the dhw side.  I just attributed it to our incoming water to the house is always ice cold in the winter.  It's been that way since we built this house.  I always figured it was taking a lot of btus to heat that water up from 40 degrees up to about 150.  I've never flushed the heat exchanger, but I haven't noted that anything has changed either.  I've pretty much been dealing with this heat loss and wood usage since day one.  I've just been trying to troubleshoot and come up back at square one.

[mlappin]

Thats pretty cold well water, never really checked the temp of ours, I know the well is about 120’ deep. Thats gotta taste pretty good when its hotter than hell and humid.