Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: oaky on May 01, 2014, 06:23:04 PM
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I'll be running my P&M BL-2840 this fall for the first time, after I get it installed within a couple of months.
I was told it is better to connect the return to the top port opposed to the bottom port. BL manual says water return should be connected to the bottom port. My old Aqua-Therm was connected to the bottom. Any thoughts?
Still cold in Wisconsin, 43 for a high, Average high for today is 65 F.
oaky
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oaky,
The Shaver Furnace returns to the bottom. I do not know what P&M recommends.
Greg Steinacher
618-401-0726
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Gassers I like to return to the bottom, conventional's to the top, the hottest portion of a downdraft gasser is in the bottom, conventional's is the top, this tends to keep the water from boiling when it is run very hot as i normally do. does not affect the warranty either way but this is the way i do it
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Do what slim says, he seems smarter than the average bear.
Interestingly enough I've looked at every brand imaginable on line out of curiosity, some brands on their sites or literature show a top return while others show a bottom.
I posted a question about this once in the homemade section. Some seem to think a top return promotes better mixing, while others don't.
I plan on taking some temp readings before insulating the next one I build.
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Water returns to the bottom always..Thats for any system
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Matty, I beg to differ, I have seen and heard water boil inside OWB's, by returning to the hottest point of the boiler you automatically get the best heat exchange, sort of like why you plumb a plate exchanger in a countercurrent flow, that is the way to get the best and most efficient exchange, when you choose to run the boiler on an efficiency mindset with very low stack temps as well as very hot water temps, you come as close to boiling as you can without going over, by returning on the bottom of a gasser and top of a conventional you are returning to the hottest point,therefor getting the best heat exchange
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Good information guys!
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I don't know which is better but I do know that the manual stated return to the bottom ports on the BL. Another thing I learned when installing the pump in said boiler there will not be much room to work with if you choose to install the pump on the bottom ports, unless of coarse your pump is not located at the boiler. My 2 cents.
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Most folks it makes no difference, we did have a couple of people that complained of boiling by going that route as they were running very hot temps and when they switched the lines the boiling stopped, this tells me that returning to the top of the B-L is better for hotter running units.
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Return water should come back to the top in a conventional folks, no question about it. This creates further mixing of the water which creates a more balanced tank of water from top to bottom, equalling potential efficiency increase and added boiler protection.
just as slim said, gassers are hottest in the bottom so returns should be there
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Thanks Scott, I'm not sure it makes a big difference if the unit is run cooler say 185 but when you run 195+ it sure does
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Ive seen conventional stoves with water boiling in parts of the water and other parts 50 degrees colder! Switched the lines around and it corrected 90% of the issue
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If you only turn pumps on when there is a call for heat, I could see the potential for heat stratification in the OWB. But if you are running pumps constantly, I would think that water movement woudl keep the water mixed relatively well.
In regards to locating pump, I do agree with CROW; I have no idea how I would install a pump off the lower connections in my CB eClassic 2400. By the way pumps are located in the house; haven't had to replace in dead of winter, YET
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The water temperature varies in the water jacket in various areas?
oaky
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The water temperature varies in the water jacket in various areas?
oaky
Yes, in some stoves like I said I've seen it be 50 degrees
Even on stoves that have proper port placement I've still seen them have a hot spot where you could hear water boiling and display temp be 180 under a hard burn
I've also used a infrared gun when doing some trouble shooting and noticed boilers with poor design, returns at the top, or a small pump would have much cooler temps in the bottom of the boiler than the top
This causes a whole array of issues, first of all u want a balanced "hot" tank of water! If you are running your stove at 165 and have 165 at the top where your aquastat probe is, and have 135 in the bottom or cooler, you are causing the ash line to be very cool inside the firebox which will lead to condensation of moisture into the ash and premature failure of the firebox.
Also, don't simply assume there is no internal plumbing inside ur boiler, because on a lot of different boilers there is pipe that put the water where they want it to go. Most returns will extend over the top of the firebox towards the front of the stove.
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The water temperature varies in the water jacket in various areas?
oaky
Yes, in some stoves like I said I've seen it be 50 degrees
Also, don't simply assume there is no internal plumbing inside ur boiler, because on a lot of different boilers there is pipe that put the water where they want it to go. Most returns will extend over the top of the firebox towards the front of the stove.
I'm not certain how the internal plumbing is designed in the BL series. This may be the reason why P&M want the return connection on the bottom?
oaky
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Water returns to the bottom always..Thats for any system
Right on, P&M is a good boiler , you'd be smart following their recommendations over some "theoretical better idea". Short circuiting the supply flow to prevent problems is a bandaid fix for other design flaws. Whether its a bad boiler design or too large of a circulator that causes very high pressure differentials that lead to flash boiling.
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I was wondering, if the water nearest the top is usually hotter, wouldn't it be better to draw the water from the top, this way, the water leaving the port, will about the same as the temp readout on the aqua-stat & you'll be getting the hottest water to the house?
It makes sense what LittleJohn had mentioned, if your circulating pump is constantly running, the water will always be mixing.
oaky
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I may or may not be right here guys but I look at the boiler as a heat exchanger, the goal of any heat exchanger is to get the maximum exchange for the least amount of energy expended, this is why the returns always come back to the hottest or supply side, the greater the differential between the 2 waters the more effective the exchange, this again is why plate exchangers should always be plumbed in counter current flow, I look at the design and determine rather the top of the boiler or bottom is going to be the hottest and then plumb the returns to it.
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Matty, I beg to differ, I have seen and heard water boil inside OWB's, by returning to the hottest point of the boiler you automatically get the best heat exchange, sort of like why you plumb a plate exchanger in a countercurrent flow, that is the way to get the best and most efficient exchange, when you choose to run the boiler on an efficiency mindset with very low stack temps as well as very hot water temps, you come as close to boiling as you can without going over, by returning on the bottom of a gasser and top of a conventional you are returning to the hottest point,therefor getting the best heat exchange
Slim all conventional owb pull from the top and return to the bottom..My OWB is set up that way.. Everyone's else's that Ive been pulls from the tops...My oil boiler in the basement pulls from the top and returns to the bottom…The hottest part of the water is the top..Why would you wanna pull already "cooled" water from the bottom..Im talking about conventional OWB's.. Not gassers.. I understand the flame burns upside down..
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I may or may not be right here guys but I look at the boiler as a heat exchanger, the goal of any heat exchanger is to get the maximum exchange for the least amount of energy expended, this is why the returns always come back to the hottest or supply side, the greater the differential between the 2 waters the more effective the exchange, this again is why plate exchangers should always be plumbed in counter current flow, I look at the design and determine rather the top of the boiler or bottom is going to be the hottest and then plumb the returns to it.
Not to be nit-picky, but shouldn't that idea follow though into furnace returns as well, the return (kept at proper minimum temperature) should be injected into the jacket closest to the flame front, or hottest point of the furnace?
Neal
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Again it is about the most efficient exchange of heat, I realize that most conventional's pull from the top, I am saying that either way is OK with me but I find the B-L series gets very hot in the top and for higher temps it may be better to return to the top on that model, all my 250's return to the bottom as that is the hotter area. Neal look at the burn chamber of an oil boiler, they typically return on the bottom and rear, they typically supply from the top front, same theory that I am promoting here.
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Again it is about the most efficient exchange of heat, I realize that most conventional's pull from the top, I am saying that either way is OK with me but I find the B-L series gets very hot in the top and for higher temps it may be better to return to the top on that model, all my 250's return to the bottom as that is the hotter area. Neal look at the burn chamber of an oil boiler, they typically return on the bottom and rear, they typically supply from the top front, same theory that I am promoting here.
I think you and I are saying the same thing. I was just trying to be clarify/understand that it wasn't necessarily a top or bottom issue, but an issue of the return going to the hottest point of the furnace. :thumbup:
Neal
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Neal you are on the money.
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Neal you are on the money.
(http://i7.minus.com/ibBMFs.png)
Money troll! (http://www.freedomsledder.com/forums/public/style_emoticons/default/lol.gif)
Neal
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Neal, seriously, do you grow fruit trees?
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Neal, seriously, do you grow fruit trees?
I'm planting some Honeycrisp apple trees this summer (seriously). Buying them at the store is more spendy that a bad cocaine habit and Obama's taxing combined!
I'd like to try some pears too. :thumbup:
Neal
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Again it is about the most efficient exchange of heat, I realize that most conventional's pull from the top, I am saying that either way is OK with me but I find the B-L series gets very hot in the top and for higher temps it may be better to return to the top on that model, all my 250's return to the bottom as that is the hotter area. Neal look at the burn chamber of an oil boiler, they typically return on the bottom and rear, they typically supply from the top front, same theory that I am promoting here.
I should have mentioned in my first post, that I wanted advice,te return would be best on top or bottom, pertaining only to the P&M BL OWF's.
I appreciate all your comments & they all are valid. I guess my main concern is keeping the condensation down to a minimum on the surface of the firebox. After installing my BL & starting it up this fall, I intend to run my high temp at, 180 F with a differential of 10 degrees.
Slimjim, your point is well taken, may I ask, with the new BL series, that include refratory cement on the bottom third of the firebox sidewalls & ends including fire bricks onte grates, would the return water heat up more quickly closest to the refractory cement (bottom), as the refractory cement & fire bricks will retain a quite a bit of heat, even at idle? My dealer had recommended having the return to the top, he had said the water at the top is the hottest so when the cooler water return, the extra heated water will act as a buffer incoming cooled water.
I want what is best for my large investment & to be good to my stove. After manufacturing P&M conventional OWF's for 30 years, I would think by now they would have worked out all the clinkers & pretty certain they have. I'm thinking it may be best if I go by their recommendation on water line hookup
oaky
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I just spoke with Brian about this and he agrees with my way of thinking, either way is OK but they will be changing the manual to read return to the top as it helps with any boiling, simply something that we did not experience until they were in the field and running hard this winter.
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Thanks slimjim, I appreciate it. Have a great weekend.
oaky
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You are very welcome Oaky, do the same!
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Neal, seriously, do you grow fruit trees?
I'm planting some Honeycrisp apple trees this summer (seriously). Buying them at the store is more spendy that a bad cocaine habit and Obama's taxing combined!
I'd like to try some pears too. :thumbup:
Neal
Honeycrisps are gooood. I'd like to find a Melrose. The old gentlemen in the area had the only Melrose apples I've found, when he retired they ripped the entire orchard out and planted it to corn :-[
I have a few pear trees at the farm. You can have the one I planted. The sob grows like a freaking weed, I gave up on pruning it and it still produces like mad.
I used to have a white peach tree, got 5 bushels of peaches off it one fall. A fungus or something eventually killed it and I haven't been able to get another peach tree to take since. They all grow for a year or two then die.
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Neal, seriously, do you grow fruit trees?
I'm planting some Honeycrisp apple trees this summer (seriously). Buying them at the store is more spendy that a bad cocaine habit and Obama's taxing combined!
I'd like to try some pears too. :thumbup:
Neal
Honeycrisps are gooood. I'd like to find a Melrose. The old gentlemen in the area had the only Melrose apples I've found, when he retired they ripped the entire orchard out and planted it to corn :-[
I have a few pear trees at the farm. You can have the one I planted. The sob grows like a freaking weed, I gave up on pruning it and it still produces like mad.
I used to have a white peach tree, got 5 bushels of peaches off it one fall. A fungus or something eventually killed it and I haven't been able to get another peach tree to take since. They all grow for a year or two then die.
Pixie Crunch is supposed to be fantastic too. I haven't tried them however.
http://www.gurneys.com/product/pixie_crunch_apple_tree/apple-trees (http://www.gurneys.com/product/pixie_crunch_apple_tree/apple-trees)
Neal
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NEVER GIVE UP/ it makes for great reading!
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Won't swear to it but I think I planted a bartlett.
I'm going to try another peach tree in completely different part of the yard, maybe whatever killed the others won't be in that part.
Fuji's are also tasty. I just don't care for red delicious, nice pretty apple with little flavor.
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Neal/ A bit fruity, soft in the squash and has a lot of grapes, the place wouldn't be the same without him!
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Neal/ A bit fruity, soft in the squash and has a lot of grapes, the place wouldn't be the same without him!
Hey, at least I didn't come from a nut tree like you! ;D
Neal
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You two are making me laugh!
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I would enjoy several cold beers with you Neal!