Outdoor Wood Furnace Info
All-Purpose OWF Discussions => Plumbing => Topic started by: themaddhatter on September 23, 2012, 10:34:25 PM
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Been battling with a "homemade" OWB system now for 5 heating seasons :bash: and I am hoping this year to whip the last few issues.
What I came into:
- Previous owner fabricated OWB: 2 feeds & 2 returns, 45 gallons of water for head on feed, 375 gallons in total system
- "homemade" underground trench consisting of pink foam insulation duct taped together as a box
- (4) 1" very old school PEX connected to boiler using hose clamps (~ 65' from OWB to house)
- (2) small circ pumps in basement (I think it was a a taco 007 & a grundfos 15-58)
- Once in basement, converted to copper
- taco ran 3/4" copper to 19"x20" water to air exchanger in furnace plenum (~25' total copper feed & return), with return passing through small modine to keep chill out of basement
- grundfos ran ~ 60 feet of 3/4" copper (total) out to detached garage (with ~ 10' of buried "homemade" PEX box again)
- all circuits are below the feeds on the OWB
Even with this setup, was in place ~ 15 years, but PEX finally failed & pumps also rust seized (2nd season in house)
Since then, a lot of has been changed. I could get into everything that was wrong, but will stick with the pertinent parts:
- Replaced both runs of old PEX with (2) 1" insulated PEX-AL-PEX runs (now there is snow between the boiler & the house) ???
- Only have 1 run connected currently in basement (homemade PEX to garage failed & haven't replaced yet, as it is under a walkway concrete slab).
- Have also disconnected the small modine on the return from the plenum exchanger (hopefully temporarily)
- Replaced all the copper to the exchanger (was buried behind drywall, so couldn't diagnose), and added an air bleeder on return
- New pump in basement (more on that below)
- Conditioned/treated OWB water, installed sediment traps & cleaned up system (now a drain down looks like drinking water instead of orange sludge)
Here is what I am looking for help with:
- Last season, house wasn't keeping very warm. OWB temp was holding steady @ 185 F into the basement (for the first time ever), but exchanger wasn't pushing hot air into house. If outdoor temp was below 30 F, couldn't keep the house @ 70 F set point.
- Checked furnace fan & cleaned. No issue there
- Two pumps were tried: a grundfos 15-58 & a grundfos 26-99. On the 15-58, it would only build ~ 6 psi after pump. The 26-99 would only do ~ 10-12 psi.
- Inlet to exchanger would read 185 f, with outlet reading 170-175 F.
- Pulled old exchanger & swapped new one in with no improvement (still have both). Also connected flow properly: in on top of circuit; out on bottom [with fan below exchanger]
Here is what I am looking for help on:
1: I am considering putting the pumps on the OWB itself to reduce the suction side of the system. That way, the pumps don't have to pull water ~ 65' and through a couple elbows. Rather, it is a straight shot off the boiler. Would this eliminate any possible cavitation I had in the old setup?
2: Given the description of the setup, what sized pumps should I be running? I believe that in the current iteration (basement pumps) that the 15-58 was not pulling the water in very well, and I think I was cavitating the 26-99, but with the pumps on the OWB, would either of these size pumps push properly? Or should I be in a totally different pump size? I was also considering building a manifold to draw both feeds into one, feeding them into the 26-99, and splitting them back out to two of the 1" PEX-AL-PEX lines. Would this work, or am I better off running two pumps? And again, what size?
3: With the 19" x 20 exchanger (capable of ~ 175k BTU), should I consider "stacking" the two in the plenum and connecting both circuits? The first heating season seemed fine, so I don't think it i s required, but it is worth asking...
4: With the two feeds coming in, does it makes sense to have them both dump into a manifold & then connect everything off of them?
5: The furnace uses a squirrel cage driven by a motor with belt. Is there any gains from changing the pulley ratios? Is there an "ideal" CFM which I may not be hitting?
6: Finally, any recommendations on a good online source for Pex-Al-Pex compression fittings to NPT? I have only connected one circuit of the underground PEX, and the company I bought my stuff from (local) is out of business. The fittings were nice (brass with 2 o-rings), and I can't seem to find them anywhere. I still have ~ 100 feet of that nice pex in the barn, and would also like to use it on other "projects".
Any info or advice would be appreciated, and you can always PM me.
Thanks in advance
Shane
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Shane. I would.for sure have pump.at the stove. I'm.running around.500ft total and.having no.issues with keeping house warm..you say orange sludge? Any possibility that the exchanger in furnace has blockage? Also you speak of pressure? This is a open system.correct? May be a issue with air bubble in your system caused by the dual.pimps with mis matched flow rates? From what tour saying you made fir updates I would think it would cook you out of your house... I would.start by moving pump.to back.of stove
You could use smaller pump..but personally.I.would.use the 26-99 and only use the.one.pump. these out guys on here are very expperianced. I set my.own.system.up myself.and works great..but there is a wealth.of.knowledge on here.. to me sounds like.you did.everything right except having pumps.in basement
..one.other thing..do.your pumps run constant...you want pump.to.run 24/7
..keeps hot water flowing.all.the time...
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Also.. i would not go to a manifold in the basement, If your running plate exchanger for hot water heater go to that first in-line then go to furnace. or if your only running furnace go directly to coil on furnace, if you hook up your garage then i would just tap into your feed side coming from boiler. basically cut the feed line and feed garage then return hook back up to feed line going to basement, but first off get that house working correct.. blows my mind you cant keep that house warm. Last winter it was -22 below one saturday and i kept house at 75.. no problems at all..
What do you think guys???? I think he puts pump and stove and make sure its running 24/7... he should be able to keep house warm as he would ever want too...
Do you have a y-strainer in loop?
personally i think you only need one feed line too. i only run 1 set of lines and im running 500 ft. dont think you need the 2 lines. just more pipe to disapate heat....
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Shane. I would.for sure have pump.at the stove. I'm.running around.500ft total and.having no.issues with keeping house warm..you say orange sludge? Any possibility that the exchanger in furnace has blockage? Also you speak of pressure? This is a open system.correct? May be a issue with air bubble in your system caused by the dual.pimps with mis matched flow rates? From what tour saying you made fir updates I would think it would cook you out of your house... I would.start by moving pump.to back.of stove
You could use smaller pump..but personally.I.would.use the 26-99 and only use the.one.pump. these out guys on here are very expperianced. I set my.own.system.up myself.and works great..but there is a wealth.of.knowledge on here.. to me sounds like.you did.everything right except having pumps.in basement
..one.other thing..do.your pumps run constant...you want pump.to.run 24/7
..keeps hot water flowing.all.the time...
Thanks for the reply back.
On your questions:
- The pumps do run 24/7, so no issue there.
- The only concern I had over the 26-99 was if it was "too much" pump. While I have the typical guy feeling of "never too much" (big blocks/forced induction/NOS/etc), there is part of me which wonders if you have too much flow, that you just blow the water through the exchanger so fast that you don't really get a chance to draw the heat off. I would rather use it, since I have it, and it wasn't cheap either.
- I do have a y-strainer in the system now (was part of my "get the orange sludge out" campaign of 2010). It is in the basement before the pump, and for about 2 weeks, I would daily dump & backflush until I got to clear, then checked weekly.
- I had the same thought about the exchanger being plugged. That is why I picked up a new one. The new one did not improve the heat issue (but is still installed nonetheless). Plus now I have the original as a backup (or a "stacked" if I need to go that route). I plumbed the fittings exactly the same with unions, so if I ever have an exchanger issue, I can close 2 valves & "hot swap" easily.
- My original intent with burying the two circuits (like it had before) was to use one for the house; one for the garage. Once I get the garage line fixed, I would like to get back to having heat out there. If I can get the house to be warm & maintain temp, I will put the small modine inline on the primary circuit after the furnace (like it was). Only reason I was thinking of a manifold now was in case I would not be moving enough volume of water in one line to adequate heat the house (1910 farmhouse in East Central MN). There is insulation in this place, but it is an old balloon framed farmhouse, so it is only so efficient (not super tight like a modern home).
Do you happen to know what circ pump you are running on your system? That seems like a wicked long run to me!
I have put a significant amount of time in fixing all the issues with the actual OWB (warped, leaky door; rotted floorpan; aquastat and draft issues), and now that this thing doesn't swing heat like crazy (would swing 50 F and often boil before, now swings ~ 15 F & never overshoots), smoke excessively, or leak water (part of the "orange sludge" campaign), I just now have to get the thermal transfer bugs out to be toasty :)
Another question: what is everyone doing to support their pumps on their OWB? I was thinking of using a chunk of unistrut and finding a clamp which fits on the casting on either side of the motor with some rubber bike tire scraps to keep from rubbing/vibrating. I don't really want to have the stress of the pump hanging freely off the OWB feeds (could see stress cracking over time). Plus the pex does expand & contract as it heats/cools, so I was going to connect it to have some slack in the system. I saw in the winter that the hot pex in the basement did expand away from the wall ~ 1-1.5" versus when it is ambient. So I want to mount the pump rigid to a bracket, put the pex inline with it (no elbows near pump), and give the pex a little room to "arc" before it goes into the earth. Hopefully, that will translate all the expansion displacement into the basement, where I have it set up to move in & out of the wall without stressing copper.
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Im running stacked Gunerfous 26-99 pumps. connected directly together. pumping 66 GPM.. no issue with lack of heat.. accually works better then other pump and uses less wood. As for mounting. they are not that heavy.. i have a street elbow coming out of boiler and directly from there to a flange. Been that way for years and no issues, this is the way most people have them hooked up.. I wouldnt waste time making a bracket. I have 2 hanging off mine and it works fine.
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Shane got a question, when pumps runnning do you hear the water flowing therough pipes, when there is air in lines or bubbles you will hear the water. When i first hooked up my 20 plate for my hot water heater. i had the issue of the plate being hot and seemed fine but when i turned water on it was cold. Hence, lines had so much air in them that it wouldnt heat. I still think you have air in the system somewhere..... you got me really thinking on this one....
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I didn't have time to read everything right now and will read through it later.
You said the pipe coming out of the heat exchanger is hot? That sounds like you have airflow problems, not water.
If the heat exchanger was way too small the water would come out near room temp.
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Im running stacked Gunerfous 26-99 pumps. connected directly together. pumping 66 GPM.. no issue with lack of heat.. accually works better then other pump and uses less wood. As for mounting. they are not that heavy.. i have a street elbow coming out of boiler and directly from there to a flange. Been that way for years and no issues, this is the way most people have them hooked up.. I wouldnt waste time making a bracket. I have 2 hanging off mine and it works fine.
There is no way possible you are getting anywhere close to 66 GPM.
For starters, your pumps are only capable of 33GPM with no no restrictions what so ever. Putting 2 in series does not increase max flow at all.
Now pumping through 500' of pex and multiple other restrictions, I would estimate that one will do around 8-10 GPM and adding the second will add maybe 2-3 more GPM.
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Well, here is what I have:
- When I turn on the pump, the copper "knocks" for a few seconds.
- I can hear the air vent (on the exchanger return on the highest point of the system) vent for a few seconds, then stop
- The biggest reason I initially was thinking about the pump on the OWB was when I went from the 15-58 to the 26-99, is that I do get a bit of the "gravel" sound at the pump aperiodically (leading me to believe I have cavitation). Whether this cavitation is inducing air somehow, I do not know).
Last year I chased the whole "must be air" in the system. Hence the air vent, new copper, and bleeder ball valves.
All-in-all, I have reconfigured the plumbing probably 5-6 times in the basement to chase the potential of air. None of them seemed to make a difference.
The system had no air valve before. Was installed last year over your same concerns regarding air in system. I also have bleeders on the ball valves before the pump and before & after the exchanger. When I turn the system on, I always crack these after I hear the air vent stop whistling (the honeywell style with the "gun bore brush" looking piece on it). I first crack the bleeder before the pump, the close it. Then crack the bleeder before the exchanger, then close it. Then the one after the exchanger. Never seen any indication that there is air in either one (always an instant stream of magma-hot water, not "spitting" or "pulsing".
Last year, also installed spigots before pump, after pump, and after exchanger. Have played with pumping DW in through these in forward-flow & counter-flow setups (was told that the pressure of DW would blow out entrapped air pockets in exchanger). Problem still there.
I am really hard pressed to believe that the root issue is air. Reason being, is that the original install had no bleeders, no vents, and used crappy gate valves (god, I hate gate valves). Literally, all that the PO had in place before was this (in path of flow):
- PEX to 90 degree copper
- Gate valve
- Circ pump
- Copper to exchanger
- Gate valve
- exchanger
- Gate valve "T" bypass setup for Modine
- Copper to wall
- gate valve
- copper 90 to pex
No temp indicators, pressure indicators, spigots, bleeders, vents, etc. Was a PITA to diagnose anything related to it, but it did work the first year without issue (the OWB itself OTOH, well that was it's own problem).
And the biggest thought about it not being air entrapment is that the entire system (i.e. every piece of connected plumbing) is actually below the grade of the OWB feed outputs. In an atmospheric system, that sort of configuration SHOULD self-bleed. But, for good measure, I still added the bleeders/air vent/spigots.
That is what drew me to my ultimate conclusion that I must be dealing with a flow issue, and putting the pump on the OWB itself.
Only way I could be drawing air in would be at a fitting somewhere, but nothing leaks, and no drips.
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I didn't have time to read everything right now and will read through it later.
You said the pipe coming out of the heat exchanger is hot? That sounds like you have airflow problems, not water.
If the heat exchanger was way too small the water would come out near room temp.
Correct. The pipe off the exchanger has ~ a 10-15 F drop across it.
The furnace is an old fuel oil unit from the 70s. Uses a squirrel cage style blower housing with motor mounted on top & vee belt connection.
Took unit out, cleaned cage & housing (very little on them), replaced belt (was in good shape, but I was in there). I have watched the blower running, and there appears to be no slipping/rattling happening.
When I pulled old exchanger, did wash out the fins, and there was a tiny bit of fuzz, but not much. Again, new exchanger did not change situation.
I do know that the squirrel cage blowers like this are not the best at moving a lot of air, but it is what it is. I had asked about playing around with pulley ratios to see if that would bring about a change. The motor has an adjustable pulley (basically, loosen a set screw, then turn on half of pulley in/out), but this will only change the diameter slightly. In looking down the pulley ratio path, I had also read you can overload the motor if you get too far out with the ratios (basically over-torquing the motor). I had also looked into retrofitting a different blower in there as well, but I could never find any tech on that.
When the furnace burner kicks on (i.e the OWB doesn't do it's job), it will keep the house warm. The furnace is set up with a two-stage thermostat: when the house is at the desired setpoint, the blower stops. When it falls below the first (highest) setpoint, the blower turns on (theoretically drawing heat from exchanger in plenum). If the OWB isn't heating the house adequately, the house temps drops to the second (~ 10 degrees lower) setpoint, and turns on the furnace burner. The furnace will maintain that temp all day long with no problem (other than burning dino bones).
Last season, I had bypassed the first (higher) setpoint, and kept the blower running 24/7, and as said, if the outdoor temp was below ~ 30, the indoor temp would not keep the house at 70. If it got much colder than 30, the furnace would kick in & keep the house at 60 no problem.
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RSI is correct, no way. I think even his numbers are a little generous
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Was a typo guys... sorry. Should be 9.6gpm . im not sure on 2nd one, i had flow meter hooked up with just on 26-99 pump.
Im guessing RSI is right. maybe both pushing around 12GPM... my point was as he was describing that he was worried about moving water so fast that it would cool down to fast.. Just saying that if that was the case i wouldnt be able to heat either. Thanks again for correction... ;D
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im jumpng in here late andmaybe way of topic but if i am reading correctly that your OWb can not keep the house warm but the oil furnace can? than i see one of 2 problems not a big enough OWF ((not likely)) or a heat exchanger too small. your heat exchanger in your plenum should be rated at the out put of your oil furnace to be sure you can match the output of the oil furnace that could heat your home.
each gpm of 180 degree water can supposably deliver to your exchanger 10,000 btu so lets say you have an exchanger rated at 75,000 btu per hour, then you need to deliver to it (at 180 degrees) 7.5 gpm to get the most you can from that exchanger. less delivery temps or less gpm will change the usable btu's
i have an exchangers ganged to gether in my huge plenum that equate to 140,000 btu max output. I run my water temps between 160 and 170 (so i am not getting the max out of my exchangers) i estimate i am only pumping between 5 and 6 gpm and have never not been able to heat the house
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I think it would be best if you post again what questions haven't been answered.
We need to know if you are getting proper airflow through the heat exchanger. Are there any gaps around it? If so, how big? I would set the fan to a faster speed. Stacking heat exchangers is a bad idea. It restricts the airflow and doesn't get it that much hotter anyway even if you get a huge fan. You are better off getting a larger heat exchanger and mounting at an angle or building the plenum larger.
Pumping water through the heat exchanger will always give you more heat output, not less. The only reason you would ever want to run it slow to allow more time for it to transfer is if it only makes one pass and you dump it. (ie, waste water heat recovery, etc)
As far as the PAP fittings, they are fairly easy to find. I usually keep them in stock and I am sure Scott has them too. Also, there should be plenty on ebay.
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I think it would be best if you post again what questions haven't been answered.
We need to know if you are getting proper airflow through the heat exchanger. Are there any gaps around it? If so, how big? I would set the fan to a faster speed. Stacking heat exchangers is a bad idea. It restricts the airflow and doesn't get it that much hotter anyway even if you get a huge fan. You are better off getting a larger heat exchanger and mounting at an angle or building the plenum larger.
Pumping water through the heat exchanger will always give you more heat output, not less. The only reason you would ever want to run it slow to allow more time for it to transfer is if it only makes one pass and you dump it. (ie, waste water heat recovery, etc)
As far as the PAP fittings, they are fairly easy to find. I usually keep them in stock and I am sure Scott has them too. Also, there should be plenty on ebay.
Good question:
Summary questions asked (& responses):
- Better off moving the pump to OWB? mw10737 said "yes". I had pretty much set myself to doing this, just good confirmation.- - Given the described setup, would a grundfos 15-58, 26-99, or "something else" make sense? mw10737 said basically "just run the 26-99"
- Should I "stack" the exchangers? You said "no", and it makes sense (more "stuff" to push air through, causes more restriction).
- Should I setup a manifold (either at OWB or in basement)? mw10737 said "no"
- Good Pex-Al-Pex compression fittings? You said you got 'em, as well as Scott (not sure who he is), or also try eBay
- Any gains from changing the pulley ratios on squirrel cage? Is there an "ideal" CFM which I may not be hitting? No real clear answer yet.
Willie G commented about water delivering ~ 10k btu per GPM. Indicates to me that I may have overall flow rate issue (i.e. cavitation). I am seeing a 10-15 F drop across the exchanger, but not throwing the required heat. Willie also commented that OWB may not be "big" enough. The OWB holds 375 gallons, and the firebox is ~ 30" wide x 30" tall x 50" deep. I can put 2 snow sled loads of wood in it a day, and it will maintain 185 F. I don't think I am pulling the max potential of heat from the unit. Again, I have 2 runs of 1" pex-al-pex into the basement (feeds & returns) which I can possibly draw from, so I believe this can deliver the required heat, just need to dump it actually into the house.
Regarding airflow, I have a piece of galvanized duct tin bent in a 90 to seal around the exchanger, with aluminum foil tape on the seams. Total unsealed area is maximum 1 in^2. This is actually more sealed than it was the first year I moved in (and the system kept the house warm then).
I would actually like to increase the overall airflow rate in the system, but I have read repeatedly about "matching CFM to the ducts (not sure if this was ever done), and also overloading (over torquing) the motor. I wager that this furnace install was in the 70's, and it is in a 100 year old farmhouse, so ducting runs aren't "ideal" by any means. I may just try swapping a smaller pulley on the motor to see what happens. Just don't want to burn up the motor/breaker/etc. I can say that you can't "feel' the air blow out of the registers, (just "feel" warmth) but I have read that this is common with the belt driven systems (my mother has a new furnace with direct drive, and her curtains "dance" from the registers).
System is only one speed: blower is on or off. I have watched the blower when it is set to "on" at the thermostat as well as when the fuel oil burner kicks on, and cannot see a speed change. Haven't actually tach'd it or put an amp meter on it, but I can (once I get the plumbing back together).
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Im Scott lol
But I'm not sure why your ot getting heat, it's not making sense to me at this point
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It sounds like you may have flow issues on both the water and the air. I would try setting the pulleys to a faster speed. Maybe check the motor after running a while and see if it is getting much hotter than it does now.
Is there any chance there is a damper in the ductwork somewhere that got closed?
You mentioned the return goes through a small modine. Is that possibly restricting the flow of the whole system?
I would go over the whole system and list all fittings, lengths of pipe and anything else. Something has to be restricting it.
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It sounds like you may have flow issues on both the water and the air. I would try setting the pulleys to a faster speed. Maybe check the motor after running a while and see if it is getting much hotter than it does now.
Is there any chance there is a damper in the ductwork somewhere that got closed?
You mentioned the return goes through a small modine. Is that possibly restricting the flow of the whole system?
I would go over the whole system and list all fittings, lengths of pipe and anything else. Something has to be restricting it.
Maybe the modine isn't made for water? Could it be for steam and have really small plumbing?
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Put a site glass in your line and you will know if your water is moving.
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Thanks guys for the input.
RSI: I agree, that it is low water flow, low air flow, or a combo of the two. I am swapping the pump out to the OWB as soon as I can find some pex-al-pex to NPT compression fittings. I think this is most likely the problem, as the furnace itself will keep heat in the house. I will double check the ducts for dampers, but to be honest, I can't remember ever seeing ANY in this system (wish there were though, as some rooms get much warmer than others). I will see if I can scare up a smaller adjustable pulley: one with the largest diameter basically the same as the current one's smallest diameter (where it is set now). That way, I can play with the adjustment. If I am still having issues after the pump swap to the OWB & playing around with the blower pulley ratios, I will lay out all the connections/fittings/lengths/etc in a drawing.
Scott: The modine may not be for water (who knows with what the PO had done), but it isn't part of the current iteration, as I physically disconnected it last season while trying to diagnose my heat issue (right now, all I have on the system is OWB->PEX RUN -> PUMP -> COPPER - > EXCHANGER -> COPPER -> PEX RUN TO OWB & some fittings/ball valves/y-strainer/air vent). I wanted to get my bearings on things before I go and muddy the waters further. Also, could you let me know if you have 1" compression pex-al-pex to 1" male NPT fittings available? I am going to do some more calling around today, but it has been odd that these aren't readily available here in North Central MN (I will be calling down to the cities today: an hour each way drive, but ISWIS).
Ijon: Good idea on a site glass. Will take a look around & see what I can find (even a flow indicator from grainger or mcmaster would work). I have used them before on some processing equipment, but I seem to remember that getting stuff which dealt with higher temps (200 F or so) were stupid expensive for what they were. That was a few years ago though, and the mind isn't what it used to be).
Again, thanks everyone for the insight. It is greatly appreciated.