Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: Ridgekid on January 08, 2012, 01:14:28 PM
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Still tweaking on my Grunfos. I've learned the following:
On my system:
@ 2 gpm I get a 30* drop across my exchanger
@ 3 gpm I get a 25* drop across my exchanger
@ 4 gpm I get a 20* drop across my exchanger
Do you look for a minimum gpm or a certain temp drop across an exchanger?
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Wondering the same thing in a low tech way. What circ speed is the best? Still have the original 3 speed circ on my NC.
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As with anything with multiple variables, there is a sweet spot. Since we can't control all the variables, we can control certain variables such as return water speed, setpoints on our boilers and furnaces. Somewhere in this is an optimal performance...maybe
I've got another question to add to this...does anyone try to insulate their heat exchangers? I have two 50 plate exchangers that put off alot of heat in my basement.
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i guess you need to know a couple of things..first how did you size the exchanger for your home heating..you should know how many btu per hour you need to heat your home, now it is said that 180 degree water will deliver 10,000 btu per hour to your home per GPM so if you think on the coldest day of the year you will need 60,000 btu per hour then you should have an exchanger that can pull that much from your water and you should be able to deliver at least 6 pgm to attain that many btu
your blower speed will also have an impact on how many btu you pull from your exchanger (i am not sure how to figure that out)
i have an "inground water furnace' that has a 2 speed blower, it runs in low speed 24/7 and since i installed my OWB it has never had to kick into high speed. i have large ductwork because the water furnace needs to move a lot of air as it does not make very hot air when and if it ever runs. i have enough heat exchangers in the plenum for 140,000 btu but i know i never draw that much with the fan in low. my water comes to the house at 160 or so and with just the furnace drawing heat it leaves at about 150, if the house is calling for heat and the doemestic water is also running the return will drop another 10
i have seen my stoves temp on a cold night and when using doemestic water and the furnace drop the temp of the OWB 5 to 7 degrees below the "blower on" temp before the OWB starts to catch up
as for sweet spot..i have no idea. i tend to lean towards that most indoor boilers say to keep your return no more than 20 degrees cooler than your delivery so i think that may be a target for us as well?
i think (not 100 percent certain) my pump is delivering about 5 or 6 gpm
i guess i would say ..oversize your exchanger (most do anyway as you should fill yoru plenum to prevent cool air from going around it)
pump enough water to keep near the 20 degree differential between feed and return.
just my thoughts..im sure others do differently
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The heat exchanger for furnace is 100k btu. The air handler is a trane. Not sure what the flow rate is. Here's the model number. twe036c140a0
I found it. It's 1500 cfm!!!!!
Sorry. That other number was the cfm of the outdoor unit fan.
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I'm not sure if there is a magic number, 20 degrees sounds good. But as far as there being an exact number that I'm not sure!
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I replied in your pump thread on some thoughts I had.
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Thanks Scott. I too replied to your added comments.
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The biggest thing is getting enough heat in the house. How much difference is the temperature of the DHW coming out of the plate heat exchanger?
Another thing is how good it is mixing the water in the boiler. It might be cold at the bottom and hot at the top. It probably isn't an issue on your boiler because most CB's hold quite a bit of water but low flow rate could cause boil over on some stoves.
If the real low circulating rate is causing dead circulation areas it may rust through faster. You might want to check with CB and see if they have a minimum recommended flow rate.I would guess your old pump was running around 8gpm or so.
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i wrap my ex with insulation . Iam loseind 30* on the coldest nights between my boiler and the ex .Iam running 007 on both sides not sure why?
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RSI - again you bring very good points to light. You are right about the return line and the controller sensing point. I have noticed it overshoots on burns about 1-2* with the lower flow rate. I need to look into this unless someone knows the minimum flow for a cb classic?
Fireboss- this discussion is about heat load across a heat exchanger. To confirm, your losing 30* before the heat exchanger? Sounds like a underground pex issue. Many discussion already started on it.
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30 seems like alot of lost heat, my return at the own is about 10 less then the temp going out I have a 140' run
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MTJag,
I say insulate the heck out of everything. My 50 plate is wrapped in duck insulation and then I stuffed fiberglass all around it, it's in my crawl space. My line set in the house I used the 1" fiberglass insulation. from Mansfield, the boiler line kind. All that hard work I put into the systems and the firewood - I want the heat to go where I need it to go - DHW and my water to air heat exchangers in my plenums.
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Let's clarify this... He's just measuring from the intake side of his hx to the return side. Not from the stove. He loses The same number of btu but the variable is the water flow, faster water loses less heat but you have to move more of it. He's running his pump 2-4gpm where many of you are 15-20gpm, he's experimenting
If your losing 30 degrees from the stove to the hx like someone said, I'm willing to bet your thermopex is soaked.
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iam sorry iam loosing 30 across the EX . I dont loose hardly anything from the wb its only 14 feet away from house well 28 if you count there and back. my house is 3000 sq . with new replace ment windows this summer. most of my house is very warm execpt my liveing room i cant get it past 65 -68 with the thermastat set at 75 the cirulater pump running all the time witch in turn cooks us out of the room that gets the heat first feels like iam chaseing a ghost
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iam sorry iam loosing 30 across the EX . I dont loose hardly anything from the wb its only 14 feet away from house well 28 if you count there and back. my house is 3000 sq . with new replace ment windows this summer. most of my house is very warm execpt my liveing room i cant get it past 65 -68 with the thermastat set at 75 the cirulater pump running all the time witch in turn cooks us out of the room that gets the heat first feels like iam chaseing a ghost
would be good thing to either use a smaller exchanger in the first one so you dont pull so much heat from it before going to the second one or...as my house is i use a feed header and a return header then pipe both rooms seperatley ( i take i you have 2 exchangers and 2 blowers now?)
could you for testing purposes block of part of your first exchanger with cardboard or a piece of tin to only draw off the heat you need and see how that works...if you are dropping 30 degrees on the first rad your second rad can not pull the heat required because the feed water is now too low for the rad to supply the needed btu
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RSI - again you bring very good points to light. You are right about the return line and the controller sensing point. I have noticed it overshoots on burns about 1-2* with the lower flow rate. I need to look into this unless someone knows the minimum flow for a cb classic?
Fireboss- this discussion is about heat load across a heat exchanger. To confirm, your losing 30* before the heat exchanger? Sounds like a underground pex issue. Many discussion already started on it.
I don't know how there could be a minimum flow for a CB..Reason why I say that..Every set up is so different.. Ive seen CB's literally tuck right up to the house..Probally don't need much flow rate..Somebody 100ft away def needs a much higher flow rate for heat demand..
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[/quote] I don't know how there could be a minimum flow for a CB..Reason why I say that..Every set up is so different.. Ive seen CB's literally tuck right up to the house..Probally don't need much flow rate..Somebody 100ft away def needs a much higher flow rate for heat demand..
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i think what you mean to say is someone who has their stove close to the house would get more GPM than someone farther away if the pumps and the lines were the same size. flow rate could be adjusted by the size of the pump if the distance is farther from the house to match that of the closer stove.
flow rate has a lot to do with btu per hour delivered to the home (that and the water temp) if you keep your water hot (say at factory setting of 180) you could get by with a lower flow rate than if you ran your water temp lower. however you need to keep your water tmep high enough that your blower can extract enough heat to accomodate for your homes heat loss. there are many variables to a homes (and yoru stoves) "sweet spot"
i say dont gamble and keep your water temp at your boiler no lower than 150 (coldest) and keep your gpm high enough to lose no more than 20 degrees drop on the return line to your blower. ( i know there are exceptions depending on how well your home is insulated and the outside air temps and the wind and such)
i guess you could lower your gpm by the heat yoru home requires on a daily or hourly basis but why not just make sure you are getting enough to heat yoru home on the coldest winter days and leave it alone?
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No, I was talking about minimum flow rate for proper circulation in the boiler. It may or may not matter on a CB but they probably designed it so the water would travel in a certain pattern inside the boiler to keep the water mixed. If it is not flowing like it should then sediment may accumulate and cause corrosion and interfere with proper heat transfer.
This may or may not be an issue just something that should probably be checked on if running only a few GPM.
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I don't know how there could be a minimum flow for a CB..Reason why I say that..Every set up is so different.. Ive seen CB's literally tuck right up to the house..Probally don't need much flow rate..Somebody 100ft away def needs a much higher flow rate for heat demand..
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i think what you mean to say is someone who has their stove close to the house would get more GPM than someone farther away if the pumps and the lines were the same size. flow rate could be adjusted by the size of the pump if the distance is farther from the house to match that of the closer stove.
flow rate has a lot to do with btu per hour delivered to the home (that and the water temp) if you keep your water hot (say at factory setting of 180) you could get by with a lower flow rate than if you ran your water temp lower. however you need to keep your water tmep high enough that your blower can extract enough heat to accomodate for your homes heat loss. there are many variables to a homes (and yoru stoves) "sweet spot"
i say dont gamble and keep your water temp at your boiler no lower than 150 (coldest) and keep your gpm high enough to lose no more than 20 degrees drop on the return line to your blower. ( i know there are exceptions depending on how well your home is insulated and the outside air temps and the wind and such)
i guess you could lower your gpm by the heat yoru home requires on a daily or hourly basis but why not just make sure you are getting enough to heat yoru home on the coldest winter days and leave it alone?
[/quote] Exactly Willie..I got a buddy who has the exact OWb as me.. Mine is a yr older..I run a 007 taco pump..Im approx 128 ft + or - to my oil boiler.. unlimited hot water.. house 72- 74F.. My buddy on the other hand... He's 85 ft + or - to his oil boiler.. Ran the factory 007 taco pump.. 007 pump could not keep up with heat demand.. thermostat set to 72 at night..wake up and it would only be like 66 F in his house.. ...Up graded to a 011 taco.. World of difference...Every situation is so different..
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I don't understand why the distance from the house would have anything to do with a minimum required flow rate.
You need the same GPM to get the same amount of heat to the house. Distance makes no difference on how much you require. It does make a difference on what pump may be needed and possibly what size pipe.
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I don't understand why the distance from the house would have anything to do with a minimum required flow rate.
You need the same GPM to get the same amount of heat to the house. Distance makes no difference on how much you require. It does make a difference on what pump may be needed and possibly what size pipe.
exactly.. and what would be (in my opinion) the "sweet spot" would be knowing how many btu you would require to heat your home on the coldest day of the year and making sure you could deliver that. if you were sure you could deliver this amount then you can deliver enough the rest of the year and that would be "sweet"
perhaps one of those 3 speed pumps and you could run it one speed for average cold days and turn it up on those extreme cold days...but for my money i like the "plug and play" technique...plug in the wood and go play..leave all else alone ;)
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I don't get how a outdoor wood boiler manufacture can give a minimal flow rate.. I can't imagine they would say for example: You need 3 gallons per min so you won't have a build up on iron and manganese..If your well water has a very high concentration iron..Your gonna have a build up of iron somewhere..Its all whats in your water really..
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Here is my rather amatuer opinion, first time fire up on a new system, you should have at least a y strainer in line and check to see what you may have "caught" if a problem arises. Weld slag, spider webs, mouse nest, all possible.
Just a thought....
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Been doing some reading.
Central boiler provides a hydronic component selection guide. On the bottom of every page it states not to exceed 30* dt. Mbtu will vary based on actual dt.
On my install the Total 1" pex installed is approx 230'. That's round trip from/to Green Dragon.
The Taco 009 rated Gpm for that amount of pex is 6.8 gpm.
Maximum flow rates: ( for CB )
1" pex = 11.5 gpm
1 1/4" pex = 17 gpm
There is a listing on minimum lengths that are dependant of pump selections. In my case the taco 009 requires at least 80' or you overload the pump.
Ok. That's it I'm tired....going to bed.
That's just some data I wanted to share..........
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Well my low tech experiment told me this:
Low speed = oil boiler runs alot.
Medium speed = oil boiler runs only in AM when calling for heat and lots of hot water.
High speed = oil boiler never runs.
Ok, high speed it is! :thumbup:
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As with anything with multiple variables, there is a sweet spot. Since we can't control all the variables, we can control certain variables such as return water speed, setpoints on our boilers and furnaces. Somewhere in this is an optimal performance...maybe
I've got another question to add to this...does anyone try to insulate their heat exchangers? I have two 50 plate exchangers that put off alot of heat in my basement.
Insulated the heat exchanger I made for hot water, it made a world of difference in the amount of heat in the room and I don't have to worry about burning myself on it. The metal gives off alot more heat than the pex lines feeding it.