Small propane tank for exp tank. Anyone using?

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Stlshrk

Member
Mar 4, 2008
166
VA
I was looking at the thread that tells us how to make a sight glass and exp tank using a hot water heater. Then I started thinking that when I buy my storage tank, could I also buy one of the smaller vertical type propane tanks to use for the expansion. Like a 100-200 gal to allow for poss future additional storage. I would plumb it similar to the description in https://www.hearth.com/econtent/index.php/forums/viewthread/11559/P15/

Anyone have thoughts on doing this? Currently planning on 500 gal storage with an Eko 40. I would think I could frame up and mount the exp tank above my storage.
 
The only down fall I see is no blatter so you will need to drain the tank of water when it fills with water over a extended period of time (1-2years). We have 2- 500gal propane tanks for storage and we have a over kill 500gal propane tank for expansion.
 
Thanks for the reply.

I had thought about that. Could that be remedied by having an air fill valve atop the tank and I could blow it down in the offseason?
Either way, still a pretty good savings and would allow me to have a tank big enough to allow for additional storage later on without having multiple exp tanks, I think...
 
Anybody else use a propane tank for an expansion tank?

I was thinking if the propane expansion tank was installed up-side-down and on top of the storage tanks, any water that expanded into the tank would be drawn back into the storage tanks as it cooled.

Thoughts?
 
Do I understand that one benefit of a pressurized system is that air can be removed and therefore less corrosive to the steel? In reading trade journals and Caleffi's free "idronics" journals, you want air separators, which is soon going to pull the air out of the expansion tank without a bladder.
 
Since I propose to put this tank as the highest point in my system, I wouldn't think that air would be displaced from the tank. As the storage tank water expanded into this tank, it would just squeeze the air inside the tank but not displace it.

From what I understand, the oxygen in the tank could be absorbed by using an oxygen scavenger or would be consumed by making a limited amount of rust. This would be a finite amount of air in the system.
 
Yes it will work, but like anything plumber said, you will have to shut off the feed to the tank, and drain the tank now and then. You will know it is time to drain the tank when your relief valve starts to overflow.
 
This quote is from the link NSearchof posted at the top of this post:

BrownianHeatingTech said:
verne said:
I was told I needed larger expansion but not how large

Okay, it's been a while since I've done this (I typically deal with non-pressurized storage tanks, so my expansion tank sizing is usually for the heating loop itself)...

If I'm using the chart correctly, you have an expansion factor of 0.0351 (assumed for a worst-case 40-200 degree reheat).

So, if you have 1000 gallons, that means you need a tank that can accept 35.1 gallons. Of course, you want to size this for the whole system, not just the tank, so add the fluid volume of each boiler, and a few percent more for piping. It never huts to over-size an expansion tank, except when you have to write a check for it... (let's call it 40 gallons, for the sake of discussion)

I'm assuming that you'll go with a non-bladder tank, due to the cost involved with a bladder tank of the size you'd need...

You typically want to size your expansion tank to never fill more than 2/3 with water. And you're going to have some water in the bottom under "cold" conditions, to make sure that the air doesn't leak down into the main tank. So I'd suggest at least doubling the acceptance volume when sizing the tank. Find an 80-gallon or larger tank, and use that. I think a used water heater would likely be a good choice. You can mount it above your propane tank, connecting to the "drain" tapping at the bottom. Do yourself a favor, and have a valve immediately after the connection to the propane tank, so you can isolate the expansion tank if needed for service.

You'll want to use a tee fitting there, add a valve and then a barb adapter facing up, and the same at the top, but with the barb facing down. Connect a high quality (don't skimp on this) nylon-reinforced clear hose between these two barbs, and double-hose-clamp each connection. This is your "sight glass" which will let you monitor the tank. The valves let you isolate it, for periodic replacement, if it hazes or leaks.

You'll have to pre-charge it with compressed air, so that's what the extra tapping on the top tee is for - add a valve, then a tee with a pressure gauge, then another valve and an air adapter of some sort (that's up to you). When you are filling, wait until you see water entering the bottom of the sight glass, then start adding pressure. You want to keep at least 10 gallons of water in there, so make a mark roughly 1/8 of the way up. Add pressure as you fill, making sure not to add enough pressure to push the water below that line. Make another mark 1/4 of the way up, and make sure the water ends up below that (this is the cold fill - it's going to go up as it heats). Record the final air pressure (do it on scrap paper, then when you've run the systen a while and are confident that things are set right, mark it right on the tank with a Sharpie).

Since it is a non-bladder tank, the air will slowly dissolve into the water, so keep an eye on that sight glass. Get used to how the water level raises as the system heats, and mark the initial "high" water line, the first time you fully heat the system from cold. As the air is absorbed, that's going to creep up. Keep a decent safety margin, and periodically drain some water and add some more air. This is what that valve on top of the propane tank was for - close it, then you can drain the expansion tank and re-adjust it without fighting the pressure in the main system. Drain it to that 1/4 mark, and re-pressurize the air to the previous pressure. Then re-open the valve on the propane tank and you're good to go.

Joe Brown
Brownian Heating Technology
www.brownianheating.com

Anybody have a feel for whether Joe's instructions would be necessary if the home-made expansion tank were mounted higher than the storage tanks, and plumbed as I've described above?
 
Dunebilly,

You think the tank would still need to be drained if it is the highest point in the system and the connection to the storage tank is the lowest part of the exp tank?

Thanks,

DC
 
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