So I'm in the process of building a new house. We are in the rough in stage and plan on getting a propane boiler for our radiant floor/DHW and then once we are moved in, I plan on building a boiler shed for a boiler and storage, which will make the propane back-up only. I plan everything being pressurized. So my question is, what do you do with your expansion tank(s)? I'll have a small one for when the propane is installed, but when I install the wood boiler with storage I'll obviously need more expansion room. So do you remove the smaller tank and install larger tanks or did you leave that tank and install more tanks in the boiler shed? Does that cause an issue with multiple points of no pressure change?
Expansion Tank Question For Added Woodboiler
- Thread starter Dutchie84
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salecker
Minister of Fire
On my system i have water in the wood boiler and storage which goes through a heat exchanger.The rest of my system has glycol which is the underground lines,everything in my house and the backup oil boiler which is also in my boiler building.I have a medium sized expansion tank for the glycol and a bigger one for the water side.
Think about putting your propane boiler in the shed after you build it.Then you will have one less flame source in your home.Which is one less source for both fire and carbon monoxide poisoning.
Think about putting your propane boiler in the shed after you build it.Then you will have one less flame source in your home.Which is one less source for both fire and carbon monoxide poisoning.
maple1
Minister of Fire
Just leave the existing one in place and add more, as needed. Should be no issues. There should only be one point of no pressure change in a circulating system, the location of which shouldn't be impacted by added expansion tanks.
To stick my neck out a bit further, I don't think it really matters much where you tie in the expansion tank, at least with boiler + storage systems - as long as it is on the suction side of a circ. I.e., don't spend a bunch of time trying to figure out where exactly your point of no pressure change is. I am not sure exactly how you figure that out anyway with accurate results, you'd have to run head calcs on everything in the circuit going forward (+) and backward (-) from the circ and see where the + running total meets the - running total. Too much brain work for me. (Might be some ignorance mixed into all that....)
To stick my neck out a bit further, I don't think it really matters much where you tie in the expansion tank, at least with boiler + storage systems - as long as it is on the suction side of a circ. I.e., don't spend a bunch of time trying to figure out where exactly your point of no pressure change is. I am not sure exactly how you figure that out anyway with accurate results, you'd have to run head calcs on everything in the circuit going forward (+) and backward (-) from the circ and see where the + running total meets the - running total. Too much brain work for me. (Might be some ignorance mixed into all that....)
Yeah I though of that "just add more at the same spot" and I might go that route because of simplicity, I was just hoping to have the added expansion in the boiler shed to shave more room to store stuff (junk) in the basement.
However (I'm not a plumber) but I will correct you on the point of no pressure change. The PNPC is Always where the expansion tank connects to the rest of the system. You are correct that the expansion tank should feed into the suction side of the circ though. That way the system pressure after the circ is always greater the expansion tank pressure. I've been doing a lot of reading [emoji12]
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Bad LP
Minister of Fire
Yeah that's probably what I'll do. I was just thinking that is for some reason isolation valves out to the boiler shed got closed somehow (Kids) and I didn't notice before I fired that then the relief would blow on the wood boiler. I could take the handles off I guess.
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maple1
Minister of Fire
I don't think I said add more at the same spot - I thought I said add more, but it doesn't matter where.
I have 3 expansion tanks on my system. New big one on the floor beside storage, a bladder tied in just upstream from my load circ. The old existing bladderless is still in the joists above the boiler, I just T'd it into the top of my boiler. Then I also added another bladderless one, under the top of my second floor steps - so about 18' above the load circ, and T'd in with the bladderless one.
You may have got me on the PONPC thing....
Maybe a pro will chime in but I was under the assumption that you should only have one connection from you expansion tank(s) to the rest of your system, that being said I have looked at a lot of builds on here and see people tee in where ever and they don't seem to have a problem. Or maybe they don't realize they have one♂️.
I'm still not sure I understand bladderless expansion tanks. I read about people using them. But don't they become water logged?
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maple1
Minister of Fire
I could see where it could cause problems, depending where Td' in and maybe other system config specifics. Example: if you had two tanks T'd in, one on the inlet side of a circ & one on the outlet, then the circ dP would I think get split - inlet pressure would drop & outlet would rise. Which might cause issues on the inlet side if it makes that too low. That's as opposed to having only one, T'd in on the inlet side - all the dP would go to outlet pressure which is what you want. But with a big bunch of storage & volume, and multiple circs to go with the multiple expansion tanks, and each tank on the inlet side of a circ, I think issues would be hard to come by. Two of mine are T'd in at the same place close to inlet of load circ. The other one at the top of the boiler is right into the top of the boiler, on its own. The loading unit is down low on opposite side via separate tappings, so don't think it has much effect on in/out dP at the circ - it is kind of mid-circuit at which point the flow frictions it between kind of make it not have much effect.
I don't think I have any problems, if they are they are small enough that I can't tell anything is wrong. Bladderless tanks can get water logged. Mainly if there is a way for air to work its way out of the system. So you shouldn't really have air vents, on a system that has one. I do have vents on mine - it is a hybrid thing that evolved from swapping old/new things in/out, some old stuff I just left as was. But the original system did have a vent, and bladderless tank, and I don't recall ever having a waterlogging episode. The risk of waterlogging likely goes down, the farther removed & higher up the tank is from the rest of the system. I left that joist tank in place, 'just because'. It was there already & had seemed to work Ok for the 17 years prior. It might have a fair amount of water in it now, after going on 6 years, I'm not sure - my pressures haven't sent me investigating it. I also did not always have the big bladder tank. When I first did the storage thing, I just used a 110 gallon LP tank for storage, on the floor beside my storage. It worked 'OK', but I did have airlocking issues, infrequent but enough to make the change. Air would work its way out of the expansion tank, and up into one of the upstairs zones. I would have to bleed the air out of the zone maybe a couple times over the winter. If I had had a place to move that 110 gallon tank, up high and away from the rest of the system, I think it would have done pretty good. But the only place it could have possibly gone up high was the second floor master bedroom - and that wasn't happening.
Then there are also the airtrol setups, that catch the air that gets into the piping, and sends it back to the top of the expansion tank. In theory at least.
I think practically speaking - as long as your static pressure is good, and you don't T expansion into the outlet side of a circ, there shouldn't be much to worry about.
(Could be more ignorance there too - I'm certainly no pro at this).
I don't think I have any problems, if they are they are small enough that I can't tell anything is wrong. Bladderless tanks can get water logged. Mainly if there is a way for air to work its way out of the system. So you shouldn't really have air vents, on a system that has one. I do have vents on mine - it is a hybrid thing that evolved from swapping old/new things in/out, some old stuff I just left as was. But the original system did have a vent, and bladderless tank, and I don't recall ever having a waterlogging episode. The risk of waterlogging likely goes down, the farther removed & higher up the tank is from the rest of the system. I left that joist tank in place, 'just because'. It was there already & had seemed to work Ok for the 17 years prior. It might have a fair amount of water in it now, after going on 6 years, I'm not sure - my pressures haven't sent me investigating it. I also did not always have the big bladder tank. When I first did the storage thing, I just used a 110 gallon LP tank for storage, on the floor beside my storage. It worked 'OK', but I did have airlocking issues, infrequent but enough to make the change. Air would work its way out of the expansion tank, and up into one of the upstairs zones. I would have to bleed the air out of the zone maybe a couple times over the winter. If I had had a place to move that 110 gallon tank, up high and away from the rest of the system, I think it would have done pretty good. But the only place it could have possibly gone up high was the second floor master bedroom - and that wasn't happening.
Then there are also the airtrol setups, that catch the air that gets into the piping, and sends it back to the top of the expansion tank. In theory at least.
I think practically speaking - as long as your static pressure is good, and you don't T expansion into the outlet side of a circ, there shouldn't be much to worry about.
(Could be more ignorance there too - I'm certainly no pro at this).
@Dutchie84, I'm in the process of adding a wood boiler and unpressurized storage tank to my existing oil boiler and baseboard system. The existing system has a 2.5gal expansion tank immediately after the oil boiler on the main line before it branches to the zones. (Truth be told that should have probably been a little larger but I didn't build it.)
I decided to add a 2.5 gal expansion tank to my wood boiler outlet. In my mind, the wood boiler needs its own expansion tank because when the wood boiler is acting as a closed loop (not sending heat to storage or any zones) the other expansion tank is not interacting with the wood boiler loop. The boilers water volume is small, 35 gal in the boiler jacket and the amount that's in about 10' of 1-1/4" tubing so I didn't need it to be very large. Then when the zone valve opens and communicates with the base boards the two expansion tanks work together.
I decided to add a 2.5 gal expansion tank to my wood boiler outlet. In my mind, the wood boiler needs its own expansion tank because when the wood boiler is acting as a closed loop (not sending heat to storage or any zones) the other expansion tank is not interacting with the wood boiler loop. The boilers water volume is small, 35 gal in the boiler jacket and the amount that's in about 10' of 1-1/4" tubing so I didn't need it to be very large. Then when the zone valve opens and communicates with the base boards the two expansion tanks work together.
So is your wood boiler system separate from the oil system and the only the that ties them together is the unpressurized storage and HX?
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So is your wood boiler system separate from the oil system and the only the that ties them together is the unpressurized storage and HX?
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I'm piping mine per this layout. You can see in this layout there are two expansion tanks and that is how mine will be. Both of mine are 2.5 gal tanks.
The system is pressurized and the tank has a drop in heat exchanger that adds and takes away heat from the unpressurized tank. Water in the tankndoes not get circulated and only acts as storage for heat.
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maple1
Minister of Fire
2.5 gallons - that seems tiny to me. I'm used to way more water though. Did you check sizing with an expansion calculator?
I found an online calculator and it recommended a 5 gal expansion tank. So technically I have the right size now with both tanks installed. The oil boiler system seems tonl work fine with just the 2.5 gal so adding another 2.5 is sufficient IMO.
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