Outdoor Wood Furnace Info
All-Purpose OWF Discussions => General Outdoor Furnace Discussion => Topic started by: capon3 on October 24, 2011, 02:25:52 PM
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Just finished installing a Legend OWB. The house is approx 1,500 sq. feet. The heat exchanger is 100,000 BTU and is installed on the return side of the blower as it would have been a lot more work to put on their other side, it seems its not heating as it should when it comes out of the vents upstairs. The supply line going into it is so hot it burns your hand, the return line coming out of it is a little warm but nothing like the supply line, so the heat is going somewhere but not through my heat vents. The exchanger is approx 120 ft from the furnace. The aquastat is set at 180 degrees. It has 2 1inch pex lines and it reduced to 3/4 inch just before the exchanger the company I hired to install it put on some kind of electric valve on so when it calls for heat it opens and then it is circulated through the exchanger. When its not calling for heat it is not circulating through the exchanger. The circulating pump is a taco 007. Any suggestions are appreciated.
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Why would they reduce it to 3/4 before it goes through the coil? Or did they use a 3/4 coil? You are not going to get nearly the flow through a 3/4 line as you would through a 1 inch line. I would think your options would be to replace the lines/coil with 1 inch or install a pump with more pressure and volume. I know from experience that either would help, however the 1 inch lines would most likely do the most.
Many years ago when I first installed a furnace to my home I used 3/4 lines and ended up with the problem you describe. After a few years I installed a larger pump which helped some. When I started selling furnaces (about 5 or 6 years ago) I only used 1 inch lines and noticed how much better this worked. 3 years ago I installed new 1 inch lines to my home and was amazed at the difference it made.
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As mentioned there seems to be a restriction in the line. The valve may be too small or not fully opening. If the inlet is about 180 deg the outlet of the exchanger should be about 160.
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BoilerHouse makes a good point that I had forgot to mention. If they used a 3/4 zone valve it may be the point of restriction. I have also seen some 1 inch Honeywells that restrict water flow to almost 1/2 inch. The long and shot of it is that if your return line is dramatically cooler than the supply line it is a sign the coil is not getting enough water flow.
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I'm not sure why they reduced it to 3/4. Needless to say I was pretty upset when I came home and found it that way. The only response I got when I asked why was that it wouldn't make any difference (yeah right).
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Iam not sure how hot air units work but i have hot water base board with a 40 plate exchanger and I have a pump on both sides running continuesly and then when up stairs calls for heat the zone valve opens and the heat goes up
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Also is the 120 feet of duct between the heat ex. and the blower insulated?
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Yes it is insulated.
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as someone has allready posted, your inlet water of 180 into your exchanger should not be cooling more than about 20 degrees..if it is you have one problem with a couple of answers for it...your pump is not moving enough water or your zone valve that controls the flow is restricting the water flow too much.
i can tell you i use a taco 0011 pump and it also cuts back to 3/4 lines in the house to feed my exchanger in the furnace, it has never hot given me enough heat and the outlet on the exchanger is only about 10 or 12 degrees cooler than the inlet.
on an average 10gpm of 180 degree water will deliver about 100,000 btu per hour
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thanks willieG i was getting scared my coil is home made but the in and out are only 3/4
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Don't chase a problem prior to the valve when you have 180F at the valve. You don't have a leak so the law says the heat is being transferred to the air or is staying in the return pipe. Since you have only a warm return pipe you must be getting little flow thru the valve. I would think that even the restriction of a 3/4 valve would allow reasonabel heat. Maybe the valve isn't opening fully? Short term you could have air in the HE and return line but that would eventually clear itself. Shine a bright flashlight thru your return line and see if you have a trickle of water??
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Don't chase a problem prior to the valve when you have 180F at the valve. You don't have a leak so the law says the heat is being transferred to the air or is staying in the return pipe. Since you have only a warm return pipe you must be getting little flow thru the valve. I would think that even the restriction of a 3/4 valve would allow reasonabel heat. Maybe the valve isn't opening fully? Short term you could have air in the HE and return line but that would eventually clear itself. Shine a bright flashlight thru your return line and see if you have a trickle of water??
Not necessarily. I have seen them air locked for months and very little heat output. If there are any ball valves I would try opening and closing them several times. The surge of water when opening the valve is usually enough to force it out.
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Ok, I think I fixed part of the problem. I bled the system and it is heating better than it was, the return line is a lot hotter than it was, and the heat output upstairs is better, but I still don't think it is what it should be. Granted I am a newbie and haven't had any experience with these, but just from talking to people, I still don't think it's putting out like it should. I just wonder if my Taco 007 isn't big enough for the job. The input and the return are 1" pex (reduced to 3/4" just before the exchanger) running approx 120' one way to the exchanger. Pump is located in the basement just before the exchanger on the input side. Any suggestons as to what size pump I should have? Also thanks for all the help before.
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If you want to stay with a Taco. I would get the 0011.
Grundfos 25-64 or 26-96 are a little smaller but would probably be pretty good too. Or 26-99 if you want a little bigger. I believe the 26-99 is pretty close to the 0011 but I haven't looked at a chart for them in a while.
I am running a B&G PL36 right now on mine and am pretty happy with it so far. It will move more water than any of the others I mentioned.
There are several brands of chinese pumps that you can get cheaper. If you want any numbers for equivalent sizes for them, let me know.
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Thanks RSI, I probably will stay with a Taco that way I wont have to change the flanges.
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Flanges are universal and what will have will work with any brand.
Depending on how your pump is mounted, you probably will have to rotate them 90 degrees. The 0011 is turned 90 from the 007 too.
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bigger pump will run alot more water thru exchanger from the outdoor furnace side which in turn your house pumps are running slower thru the exchanger and robbing more heat from outdoor furnace. Also make sure your exchanger isn't hooked up backwards. Im no expert but if your loosing 20# on the return of exchanger why have one what i have noticed when a zone is first calling I would loose fifteen# at most due to the lines cooling off and whatnot while sitting waiting to flow again but after a few seconds its only loosing at most 3# on the return compared to the inlet from outdoor stove.