Any condensation problems with this?

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willworkforwood

Feeling the Heat
Jan 20, 2009
465
Central Ma
After reading the post from HR on the "Return temp" thread, I started thinking (again) about possible condensation with the way I'm using my boilers. With condensation damage being such a big deal, and also something you apparently don't see until it's too late, it seems like a good idea to ask the pros. Our house has lots of South-facing glass, and on good sun days, we can solar heat the house, even at 20* outside. On sunny days, we'll let the WB run down to empty, mid to late morning. We shut it off with the water temp usually at 170-180. The OB (in series) is also shut off at the same time (and same temp of course), along with all circs. Now there is no flow in the system exept for some DHW being pulled from the Superstor. Depending on the Weather, we can leave everything off from 5 to a max (so far) of 12 hours. After a little bit of trial-and-error, we've become good at judging when the WB needs to be fired back up in order to reheat everything at the right time. At refire time, the WB water temp has dropped to 100-140, and the OB from 90-130, depending on length of time down. The refire sequence is WB comes back first alone, and when it hits 155 the circ to the OB loop kicks in and reheats the OB. The zone circ stays off until both boilers are back to around 175, and then we turn the zones back on as needed. This has been working really well (much better than I ever imagined it could), and has saved a ton of wood with no oil used in the process.
I thought that with no flow, and the boilers just cooling down gradually, there would be no condensation issues. But now I'm wondering about "reverse condensation" in the OB - when it's temp is 90*, and then being immediately hit with 155* from the WB. Does anyone see any potential problems with what I'm doing?
 
I have basically the same set-up in my house. You could get some condensation as you WB temp is coming up but it would be the same with the danfoss or whatever temp valve if you had one on it for the same amount of time. I run my boiler nonstop and don't have any problem of it getting below 140 because the circulator shuts off at 145. I should have said in the post on the other thread that if you have an aquastat on the boiler that turns off the circulator when the boiler temp gets around 145-150 then I would never use return protection unless it's a large amount of return water such as storage, radiant or storage. I've never replaced a boiler damaged from condensation in my 22 years of doing this. I do have one to replace this week that some idiot put a 009 circulator on a cast iron burnham with radiators and ended up cracking the side of it.
 
I could be wrong but I've understood the condensation damage occurs when it is allowed to happen repeatedly through the entire burn not just from bringing your system up to temp. My homemade water to air heater (air conditioner condenser) will take 180* water and the 3/4" return line feels ice cold coming back. It's a good thing it's mixing with the return of my dinky Modine style heater that probably has a delta T of 5* if it's lucky. The circ running both of these heaters is tied to an 1 1/4" primary loop about 15' long so their should be plenty of mixing going on. I have a well thermometer on the primary loop in a tee with along with the fill valve (needs to be moved to its own tee directly in the primary loop stream) that is reading 140* when the boiler is at 186*. Won't know for sure until I move the thermometer, but I would guess it should be reading about 150* at this time. That's a 35* delta T! I had about a 1/3 load of dry walnut & some elm and the EKO 40 hovered at but never went above 186* running full tilt. I guess my point is you should definitey measure your return water temp especially if running w/o a mixing valve, loading device, or the new style variable boiler circs. FWIW I'm using a 1 1/2" 140* Danfoss but it is bushed down to 1 1/4" on the input & output to match the rest of my close boiler piping. The boiler return input is only 1" and I keep that valve about a 1/3 closed. I also changed to EKO settings to not turn on the boiler circ until it was 170* and shut off at 165* I believe. It used to be at 150* but the boiler would never reach the 165-185* range like I believe it should. Let's see what the pros say but I don't think there is anything wrong with your startup procedure. It would give good piece of mind to know what the return water is coming back to your WB though, maybe you can tell from the OB if it is plumbed between your WB and loads. Wish I had that much solar gain. Mine is definitely noticeable but not enough to go without heating.
 
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