Sidearm heat exchanger problems

Mare Posted By Mare, Dec 27, 2007 at 2:28 AM

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  1. Mare

    Mare
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    Dec 27, 2007
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    We just installed a Central Boiler OWB 2 weeks ago. Everything seemed to be working fine up but now it seems we run out of hot water. We have a sidearm heat exchanger hooked up to our oil 30 gallon water heater. I read the other posts here on this topic and from what I understand from them, I would believe it is working fine. The horizontal pipe that runs out of the top of the exchanger to the anode port on the tank is extremely hot. The water as you first start using it is also extremely hot. If you make a constant draw of hot water though (eg. 2 showers in a row), you lose the hot water. At times you can go to the bottom of the exchanger and draw water out that is extremely hot and sometimes it really isn't. I turned the oil burner back on but set the thermostat to 100 degrees and on a constant draw, it will kick back on again. Can someone think of something that can be wrong? We drained the tank to install the exchanger which I would imagine took care of the sediment on the bottom of the tank. The anode rod was quite a site though, looked like white swiss cheese. We purged the air out of the tank (or so we thought we did) at the top elbow of the exchanger set up. Any help would be appreciated.
     
  2. Eric Johnson

    Eric Johnson
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    Nov 18, 2005
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    Welcome to the Boiler Room, Mare. I have a sidearm and I have been thinking about your problem. At the moment, I'm thinking that maybe putting a circulator on there might be a solution. Sidearms work slow by nature, but with enough storage capacity, they can usually keep up with most domestic water needs. But being gravity-fed, they don't respond well to large demands. If you only have a 30-gallon tank, I'd say that the sidewarm is working OK, but it's not getting enough storage capacity to keep up with your hot water demand. You might want to consider adding another hot water tank or replacing what you have with a 50- or 80-gallon tank. Or, as I mentioned earlier, put a circulator on the water line to speed things up. The hx is not the problem--it's the rate of flow through the hx and/or the storage capacity of the hot water heater.
     
  3. BrownianHeatingTech

    BrownianHeatingTech
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    Oct 5, 2007
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    Assuming it's piped correctly...

    Sidearms are not as efficient as other sorts of heat exchangers. It may simply be incapable of keeping up with two showers in a row, depending on your setup.

    Joe
     
  4. Mare

    Mare
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    Dec 27, 2007
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    Thank you so much for your replies. One thing that does concern me is that because it is an oil water heater the drain is further up the tank to allow for the combustion chamber somewhat like a gas heater but just a tad higher up. This makes the exchanger extend approx 10 inches above the top of the tank. With all the diagrams of all the instructions, the horizontal run from the top of the exchanger to the anode connection should be 4 inches or less from the top of the tank (I'm assuming this is part of the gravity concept). Ours isn't. If we were to elbow down to the 4 inch level do you think that would help us out?
     
  5. rowerwet

    rowerwet
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    everything I've seen about sidearm HX says no more than 4" above the tank for gravity feed, with a circulator it wouldn't mater.
     
  6. 700renegade

    700renegade
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    Nov 20, 2008
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    I'm suspicious about your air purge on the 3/4" line that feeds into the old anode location. Do you have a air bleeder vent on that section? if not, I'd start there. You have to have ALL the air out of that section of line or you will get very restricted flow. An air bubble that occupies 3/4 of the line is just like having a valve 3/4 closed. There is no velocity in there to push the bubbles out. Also the 10" above the tank is probably an issue - it works against the thermocycle function. you may need to cut apart and resolder the fittings to get it as close to flush w/ the tank as possible.
     
  7. Duetech

    Duetech
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    Sep 15, 2008
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    Sidearm exchangers do not have to be perpendicular. They can be attached at an angle to avoid extending above the top. Convection or gravity heat will work at just a little above level but will be slower. You can still angle the sidearm with plenty of pitch. I had my sidearm installed on our old propane water heater for about a week and lost my hot water even though the sidearm was hot the water in the tank was not. I drained/purged the tank before hooking the sidearm on so I thought I was ok. Curiosity got the best me so I decided to drain/purge the tank again. I got more crud the second purge than I did the firs time. Been working fine now for two years and gives more hot water than the gas did. I think the hotter water from the boiler loosened scale off the inside of the tank.
     
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