Outdoor thermal storage?

I was talking to a friend about my system and explaining to him how sometime in the future i was planning to add storage. I also posed to me that it was going to be difficult because i am limited by what i can fit through my bulkhead if i want to use pressurized storage. He suggested that i just buy some big tanks and bury them outside. I've hard many many people say that you can't do this but i have never heard anyone explain why. I searched this site and can't seem to find anything. If the tanks are buried at least 4 feet down so they are below the frost line then they won't be at risk of freezing. To get to them you could use the same insulated tubing that is used for outdoor wood boilers. As long as they are heavy steel and they are coated properly they shouldn't corrode. I'm sure that they could also be insulated and then fiber-glassed like some of the newer more efficient water heaters and that would not only insulate but also protect them from moisture.

Can someone explain to me why you can't have outdoor in-ground thermal storage?

I don't have a garage or i would have considered putting them in there before burying them. We'll see how it goes, in the end i may just go with unpressurized storrage if that is the only thing i can get to fit in my basement. I have also considered trying to build a tank. I have noticed how my boiler is constructed and i think i could possibly build a tank out of 1/4 inch steel that would hold the pressure. Of course that would be my last resort as the tank would be large. i was figuring a reasonable size would 4x4x6 1/2. It would be about 780 gallons and once it is in there and built the only way to get it out would be to cut it up. The other thing i've considered is possibly building 2 or 3 smaller ones that would fit through my bulkhead and pipe them in succession. If i calculated right, a tank about the same size as my Tarm OT-50 would hold 300 gallons if it were just an empty box. If i could figure out how to fit a couple of those in my basement in succession i could get my 800 to 1000 gallons of storage. Of course that would require quite a bit of plate steel and i think that might get expensive. I've also considered opening up my bulkhead more. The doorway is about 34 inches wide but the actual width of the the bulkhead is about a foot wider. It would mean removing about 6 inches of foundation on either side of the door. I don' think it would be that big of a deal because it doesn't go to outside it just goes into the bulkhead, and i don't think it would have any real effect on supporting the house at it is only 6 inches. That could possibly be either cheap or free because i know someone that does concrete cutting and would do it for me. In the end that might be my best option because it means i would be able to get bigger tanks into my basement. Of course i'd have to ask someone with structural knowledge to be sure before going that route.

maple1 said:

110 & 330 gallon propane tanks are 30" diameter. If that helps.

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Are the 330 tanks vertical or horizontal? Do you know how long or tall they are?

i thought the vertical ones had a ring on one end to balance them on. Of course that could always be added after i get the tank too.

jeffesonm said:

I have three 800L (211 gallon) tanks that are 30" diameter and <7' long I would sell you if interested.

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Thanks for the offer but i'm going to have to pass for now. I just spent a bunch of money on installing a boiler and buying wood. I need to recoup some of the money I've spent before i think about spending more. Right now i'm just thinking about the future. Maybe 2 or 3 years down the road after this boiler has paid for itself then i can think about reinvesting the money on some storage.

if everything is below 4 feet in the ground would you still need to use glycol? I was only thinking about the possibility of doing it without glycol. I do agree with you that i'm risking a lot if it has glycol. I would definitely not do it with glycol in the water.

What about in a shed? I have a shed that is about 16x16. Could i run lines out there and install the tanks out there safely, or would i lose too much heat getting the hot water out there?