Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: ssr on November 24, 2011, 09:15:16 PM
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I AM A NEW MEMBER TO THE SITE.BUT NOT NEW TO FABRICATION.I'VE BUILT A OWB THAT IS A LITTLE OVER 300 GAL. WITH A 32''X42''
FIRE BOX IN IT. IT IS ALL INSULATED REAL GOOD.PROBLEM IS I GOT 2800' FT. OF 1/2'' PEX IN MY CONCRETE FLOOR AND CANT SEEM TO GET IT WARM NO MATTER WHAT I DO.IF THE BOILER IS NOT CIRCULATING I CAN GET IT HOT AS I WANT IT.BUT WHEN I START CIRCULATING IT THROUGH THE FLOOR IT JUST WONT RECOVER.MY PUMP IS 40GPM AND 30 FT HEAD. I KNOW YOU DON'T WANT THE WATER HOTTER THAN 120 DEG. IN THE CONCRETE BUT WHEN ITS CIRCULATING I CANT EVEN GET THAT CLOSE.ANYONE GOT ANY OTHER IDEAS.I GOT A MIXING VALVE ON ORDER SO I CAN GET THE BOILER AROUND 170 THEN SEND 120 DEG WATER TO THE FLOOR.IE TRIED ALL I CAN THINK OF.THE BOILER I BUILT IS OFF A SHAFER DESIGN. IM RUNNING OUT OF IDEAS HELP.........
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here is a pic
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2800 ft all on one loop??
Normally radiant heating is done in zones and 300-400ft with zones valves and pumps coming off of a header system. The shaver design is not nearly as efficient as some IMO but it should do what your asking.
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no sorry the longest run is 300 foot . i got 10 loops running to one manifold.1'' pex running to the feed manifold. and 1'' running from the return manifold to the boiler
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It is going to take a while to get things heated up, why only 120 to the concrete?
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Oh and Welcome to the site
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ive had it going for 2 weeks.i heard you dont want it above 120 degree or it will start busting the concrete.its just not coming around.the concrete is 6'' thick with 2'' foam under it it and the pex is 2'' from the top.
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thanks for the welcome this site is great for all the people like me
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Yea, don't get it over 120. Actually about 100 should heat it. What is the problem? The furnace can not keep up or you are not getting hot water through the system? If its the furnace not recovering then I would ask if your pump runs all the time? If it doesn't I would bet you don't have as much storage as you may think. The water on top of the water jacket may be hot but without the pump running it will not mix and the water below the firebox will not be as hot. The ideal way to do a infloor system is to have the pump on the furnace run 24/7 and the pump for the floor to stop and start. This way you can slowly adjust the mixing valve to a position that will allow the furnace to maintain its temperature while pulling some heat into the floor.
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I ONLY HAVE ONE PUMP FOR THE SYSTEM,IT IS INSIDE THE SHOP IT IS 50' AWAY FROM THE BOILER.IM SURE THE TANK IS 350 GAL.THE HOT FEED IS TOWARD THE TOP OF THE TANK.AND THE RETURN IS AT THE BOTTOM,ON THE RETURN INLET ON THE TANK I MADE IT RETURN UP BY THE FRONT OF THE BOILER SO IT WOULD HAVE A LONGER TIME TO MIX.I MUST BE MISSING SOMETHING.I THINK THIS SYSTEM SHOULD BE PLENTY TO HEAT A 40X 60 SHOP FLLOOR.BUT I COULD BE WRONG. ANY HELP IS ALWAYS GREAT
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Unless it is redirected inside, my HeatMaster has the return going in at the top and the supply feed is on the bottom with circulating pump. Im not knowledgeable about which should go where or whether it makes a difference or not but that appears to be how mine is connected.
I just looked at the Shaver design, I am perplexed as to why they designed their system to heat the hot water at the OWB. Additionally, it appears you would need more pex tubing. Is this more efficient or have some advantage? I cant make sense of it.
Anyways, good luck!
Michael
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Mcarter. That's just kinda the old way of doing it so to speak
I know that most stoves I've fooled with have the pump pulling out of the bottom and returning to the top, better mixing that way I suppose
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The reason to have the supply on the bottom is because it helps mix the water in the furnace. Hot water rises, cool water sinks. When you pump the cooler water into the top it will naturally falls which mixes the water nicely in the furnace. If you only have one pump on the whole system you have to be starting and stopping it. I would guess the majority of water in your furnace that isn't all that hot and so when the pump kicks on you use the hot water on top rather quickly. Also the water coming back from the zones is going to be cold from being in the concrete so you are pumping cold water into lukewarm water. Add to it the fact that shavers design isn't as efficient as many models and I would say all of that together is your problem.
Scott, what do you think? Am I missing anything?
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first thing i would do is check at your OWB how many GPM are being returned to your boiler (i think your system would require at least 10)
you say you have 2800 feet of pipe in your floor-----how many square feet is your floor?
as some one has allready suggested, your OWB should have a line that allows water to circulate to and from the OWB 24/7 and your floor loops should be controlled with a pump (such as a pump hooked with a zone valve controlled by a thermostat)
when you say thiings just wont recover, do you mean your OWB will not recover to yoru set temp?
you should be using a mixing valve and have your floor temp about 100 to 110 (i think that is average..i have run mine as high as 120)
what you shold be lookinig for is a delivery temp from your OWB to the return temp of the OWB to be no more than 20 degrees )say 160 in and 140 out) this should allow your OWB do recover if it is large enough for the amount of btu you are drawing off it.
if this is the only draw you have i am "guessing" you are (or need to be) drawing about 80 to 100 thousand btu per hour and this would mean your pump needs to be delivering at least 10 gpm to the floor header.
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The reason to have the supply on the bottom is because it helps mix the water in the furnace. Hot water rises, cool water sinks. When you pump the cooler water into the top it will naturally falls which mixes the water nicely in the furnace. If you only have one pump on the whole system you have to be starting and stopping it. I would guess the majority of water in your furnace that isn't all that hot and so when the pump kicks on you use the hot water on top rather quickly. Also the water coming back from the zones is going to be cold from being in the concrete so you are pumping cold water into lukewarm water. Add to it the fact that shavers design isn't as efficient as many models and I would say all of that together is your problem.
Scott, what do you think? Am I missing anything?
Nope, I think what your saying is right on track. Im not sure yet that it's all of his problems but it's sure a good place to start. He needs that stove cranked up and a zone valve/mixing valve.
But, like your saying, I don't think the water inside his stove ever has a chance to mix properly.
Hey ssr, how thick is your firebox???
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the fire box is 1/4 '' thick 32'' dia. and just shy of 40'' long.switching around the inlet and outlet might be a good place to start,after it was brought up.the pump i got pumps 40 gpm per minute and 30 ft head. hopefully this is big enough.im getting the mixing valve next week .ill install it also . thanks for everyones input. im pulling my hair out on this project, i spend to much more money on it the wife will hang me.lol
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your pump sounds like it should be fine. your floor loop should only be around 10 feet of head (i think) like i said earlier pull the return line off at the OWB and see how many GPM is returning from your system then you will know for sure.
also as i stated before the return temp should never be more than 20 degrees less than your feed temps. most in floor radiant temps should only be between 7 and 12 degree drop from feed to return
when your floor system is calling for heat and you say your stove cant recover...it MUST recover at some point if it is working at all,,what i mean is the water temp at the stove should reach a point where it does not go lower..
also how is your stove fed air...naturally or forced?
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How many brands out there pull the supply water from the bottom? You guys have me scratchin' my noggin now. I dug up my installation and operation manual for my P&M 250 to make sure I'm doing it right. It shows several pictures of supply water being pulled from the top ports and return water being directed to the bottom ports. My friend's CB 6048 is hooked up that way also. Our systems use the pump as a "pusher" on the top ports, with no other pump in the system.
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martin, my home made is the same i have never had a problem with temps
perhaps the OWB cycles a little sooner than the other way but the water (if your pump runs 24/7) is always mixing. yes i agree that the hot water rises and if you put the cold in the top it will mix well. but i also think that if you are pushing 10 or 20 gpm into your tank it is mixing at a good rate as well. i mean lets face it..water going out the top is being pushe back in the bottom and your stove is always holding the same amount of gallons so what goes out the top has to be replaced with something. also if your system is operating properly (and sized properly) there is likley only a 10 or 12 degree difference between feed and return
i have seen some stoves where the feed and return are on opposite sides of the stove?
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How cold is it getting up there? Supposed to get up to 58* or 60* here tomorrow. It's 50* right now.
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52 rigth now and supposed to stay near that for the next 4 days
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also how is your stove fed air...naturally or forced?
it is fed by a fan in the front door.i got the fan blowing under the fire. it is around 120 cfm. and i got a reastat on it to adjust the fan speed 1-10 .i can run the fan at what ever speed i want. good info on here
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ok your stove never recovers how do you mean?
1 does your stove never get back up to your set temp?
2 does your fan ever shut off ?
3 does your stove "settle" at a lower temp (i mean does your stove say...stay at 70 or 80 degrees, it must settle somewhere?)
4 do youknow at what temp your water is entering your floor loop and what temp it is returning to the boiler?
5 have you determined the GPM flow returning to the boiler?
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You are correct that it doesn't matter all that much where the supply/return is. However with him starting and stopping the pump it only adds to the problem. With 2800ft of pipe full of cold water you need plenty of reserve to be able to pull from when the system kicks on. One thing I have learned from radiant in floor systems is that you can waste a lot of heat by pumping in water that is too hot. What you really want to do is slowly heat the floor up evenly and then it shouldn't take as much to maintain. Radiant heat systems are much slower systems than forced air systems. As WillieG already suggested you need to only pull a portion of the heat off the outdoor furnace. To do this properly you need two pumps and a mixing valve.
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the water in my floor loop leaves teh loop anywhere from 80 degrees to 110 but meets up with the water in the return header that is anywhere from 135 upwards
my floor loop is set up that the floor loop itself is always circulating..when the themosta calls for heat the zone valve opens and the mixing valve does its thing.
http://i67.photobucket.com/albums/h308/billie_boy7/P2120004.jpg (http://i67.photobucket.com/albums/h308/billie_boy7/P2120004.jpg)
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willie g
THE FAN ON THE BOILER DOES VARY RARELY SHUT OFF.
THE FEED TEMP AND RETURN TEMP ARE AS MUCH AS 45 DEG APART ALOT OF TIME.THEY ARE NEVER THAT CLOSE.
I HAVE NOT YET GOT A EXACT GPM ON THE RETURN LINE.I GUESS I COULD JUST DUMP IT IN A BARREL AND TIME IT OR WHAT.
THE WARMEST THE AMBIANT AIR TEMP IN THE SHOP WILL ONLY STAY AROUND 55 DEG. AND THAT IS WITH THE BOILER CRAMED FULL OF WOOD WITH THE FAN ON HIGH CHEWING UP WOOD.
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Well the heat is going somewhere. I guess you have insulated pipe between the shop and furnace and insulated below the concrete?
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there is 2'' insulation under the concrete.i dont have insulated pipe in the ground,but it is ran 4' deep in 4'' pvc for only 50 ft.
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there is 2'' insulation under the concrete.i dont have insulated pipe in the ground,but it is ran 4' deep in 4'' pvc for only 50 ft.
Well.... There is a big part of the problem. It doesn't matter if it's 4" deep or 4' deep. Once the heat leaves the pipes it's gone and your not getting it back. It doesn't matter if your heating the air around the tubing, the dirt, whatever. When it's gone it's gone. That's why the insulated pipe is so important. It wouldn't surprise me if 30 degrees of the temp difference in supply and return is simply lost in getting there.
If youve got a roaring fire and no results. Well, the heats going somewhere.
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This is one of the most common problems I see in DIY owb's is people skimp on the pipe and think PVC is somehow an insulator. Ive seen folks make there own insulated pipe, some of it is "ok" but not as good as a true quality triple wrap. They usually end up over 4 bucks a foot in DIY pipe, I don't see how it's ever worth a couple bucks a foot to run into problems and have to do all the work involved with it.
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i was going to get the insulated pex but i was told in that short of a run it would not be worth it to do so.
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50ft is a pretty good run, that's 100ft of un-insulated 1" pex.. Willie had some numbers on how much btu were lost per our per foot, I'll find them
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there is 2'' insulation under the concrete.i dont have insulated pipe in the ground,but it is ran 4' deep in 4'' pvc for only 50 ft.
If you have the PVC sealed and no sharp bends, I would pull the pipe out of it and buy triple wrap and pull it through. (take out of the outer pipe it comes in)
To see how much heat you are losing, you could make a bypass at the floor loops so no water goes through the floor and check the temperature drop.
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General Outdoor Furnace Discussion / Re: D.I.Y. Pex line insulation?
« on: October 28, 2011, 07:43:57 PM »
ball park figure here of heat loss of 1 inch uninsulated pex pipe burried inside a hollow air filled pipe..somewhere in the area of (this is a guess and likley a low ball one at that) 40 to 50 btu per foot per hour
for easy figuring lets say 50 btu per foot per hour. you say 400 feet (is that one way?) this could be 800 feet round trip taht gives us 800 x 50 btu that give us 40000 btu of heat loss per hour or 960,000 per day that in my opinion would be about wasting one years wood supply each year
now i am basing this on only guessing as i have figures for copper pipe that use an hot temp of 140 and the outside temp of 70 (1 inch copper would lose about 30 btu per foot per hour) i beleive that pex would not lose heat as fast as copper but in the scenerio we have, we would have a temp spread much larger 180 in the pipe and only about 50 in the air around the pipe and then the dirt around the air would be drawing a little ahrder as well so i say 50 btu per foot of pipe per hour is a fair number to use? (some one maybe able to do better)
these are just guesses but i can tell you this..when you see 400 feet of thawed ground in mid january that is about 2 feet wide you will say...AH HA that is where all my wood is going!
Compliments of willieg
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In regards to willies figures, I think that 50 btu is a low estimate, just my opinion. So, you can figure out where a lot of your btu's could be going.
However, I don't think there is one major thing causing your problems. I think it's a combo of a lot of things, pump on top and starting and stopping the pump could cause mixing problems, lack of zone valve and zone pump, the un insulated line, and if it's a shaver copy that's not a real efficient design but it should do what your asking once you figure out this other stuff
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holy smokes...those uninsulated pipes are going to cost you wood and plenty of it..however i agree with scott that there are many things contributing to your problem.. if you fix all the ones but your underground pipe your stove should do the job but you will be wasting lots and lots of wood you burried your pipes deep but without insulation they will still be giving up many thousands of btu's
i am not sure how you could let someone tell you that in that short of distance you dont need to insulate, after all you insulated below your cement floor?
you do need to insulate that underground pipe. there is no way i know of that can show you how much heat you are losing because if your pump in moving 40 GPM you may or may not see a dramatic heat loss? But rest assured you are losing way more heat to the ground than you should be willing to give.
my pipes were 3 feet down and when they got waterlogged you could see a strip in my yard that was 2 feet wide in mid january that never had snow on it more than an hour or two after a fresh snow
my water logged pipes i think would draw more heat off than pipes in a tile but you are still going to lose mega btu's