STORAGE QUESTIONS

[Outlaw]

I have an Atmos boiler 85000 BTU's I am just starting the heat storage building process now. I have a 500 gallon propane tank to use for my storage.
My question for today is, what do I need for a expansion tank? How big of a tank, what brand, model, make , serial number? What can I use instead of a new expensive one?
Any help would be greatly appreciated.

Thank You!

 

[Nofossil]

I have an Atmos boiler 85000 BTU's I am just starting the heat storage building process now. I have a 500 gallon propane tank to use for my storage.
My question for today is, what do I need for a expansion tank? How big of a tank, what brand, model, make , serial number? What can I use instead of a new expensive one?
Any help would be greatly appreciated.

Thank You!

Another Vermont member - welcome to the forum!

There are a few threads on this topic, with MANY different solutions. In a classic true pressurized system, there's a rule of thumb as well as an actual equation, neither of which I remember. Seems like 500 gallons of storage needs about 40 gallons of expansion room. If you have a freeze-proof high point in your system, semi-pressurized is an option. Essentially have an open tank at the highest point with an overflow to avoid disasters.

 

[stee6043]

I have (2) 66 gallon tanks from Elbi for my (2) 500 gallon storage tanks. I purchased them through Cozy Heat (sponser of this site)....

ETXTV-110 XTV-110 Elbi Expansion Tank - Stand

 

[Outlaw]

Freeze proof high point, hmmm perhaps that would look good in the living room... I'll have to think on that one a bit, maybe disguise it as a coffee table?

Seriously, that won't work for me as the house is a ranch, and the boiler room is in the celler. So 40 or more gallons it is, thank you very much for the quick response.

 

[stee6043]

Freeze proof high point, hmmm perhaps that would look good in the living room... I'll have to think on that one a bit, maybe disguise it as a coffee table?

Seriously, that won't work for me as the house is a ranch, and the boiler room is in the celler. So 40 or more gallons it is, thank you very much for the quick response.

All you really need is roulghly 30' of room above your boiler. Basement plus main floor plus attic might make it work...and the size of the pipe doesn't need to be anything specific - whatever you could fit.....

 

[Outlaw]

30 FEET? or 30 inches? When the system is pressurized what keeps the expansion tank from filling all the way to the top and out the overflow?

 

[emesine]

33 feet of vertical pipe (can be very small diameter no problem) will give you one atmosphere or about 15 psi. This will "pressurize" your system. 15 feet would give you about half that, don't know if that would be enough or not. In terms of overflow, what I would do would be to get your whole system up to temperature, thermal storage full, boiler firing, etc. Then fill up the overflow tank. When your system is hot is the largest volume. As the system cools the water will contract, and the water you put in your overflow tank will go to fill up the system. If you fill it when the system is hot, you shouldn't have any spills...... theoretically

Andrew

 

[dogwood]

I am getting ready to size my expansion tank for a pressurized system also, and have a beginners question or two. Are there other factors besides the pressure maintained in the expansion tank that determine the amount of pressure in a pressurized system? Answers in this thread seem to indicate the height the pipe rises is a factor. My 1.25" pipe will have to rise about ten feet to the attic space. How do adjust the pressure to where it needs to be? I have 1000 gallons of storage and anticipate getting an 86 gallon expansion tank, although I have to do the calculations to be sure this is right. I am planning on getting a Solo Innova. I'd appreciate any information any of you might share. Thanks

Mike

 

[stee6043]

First - you don't need the tall vertical pipe being discussed above if you have expansion tanks. The "tall pipe method" is a way to have a semi-pressurized system which would eliminate the need for expansion tanks. Having expansion tanks is much easier and cleaner, in my opinion. I think what drives some people to using the pipe method is that some local code authorities will not allow non-ASME pressure vessels in residential applications. By going with the open pipe you're not technically pressurized and presto - easier to get approved in some cases.

As for the pipe - it's Physics 101. Every 33 feet of a water column generates one atmosphere of pressure. Typical closed-system boilers run at or near 15psi (roughly one atmosphere). So by installing a roughly 33' piece of pipe straight up, open on the top (typically with an open tank to catch overflow) you can have your proper operating pressure without the need for tanks.

Again...it's much easier to deal with expansion tanks I'd say. You simply charge the system to the proper pressure with your garden hose (or however you fill it) and you're good to go. No need to deal with overflow in the attic, etc....

 

[Gooserider]

I will admit it's a bit of a trade-off as to which is easier to deal with, the "tall pipe" method, or expansion tanks...

The tall pipe obviously reqires the right physical setup, if you can't get about 30 feet of vertical distance between the boiler and the top it isn't going to work... You also need to have the room in the attic for the tank, and the floor has to be up for the load (The tank has to be able to handle about as much volume as the "acceptance volume" of the expansion tanks on an equivalent system...) If running a non-pressured storage system, this is no big deal usually as the required volume is pretty small, but a pressurised storage system will need a big tank, which can get very heavy, very quickly...

OTOH, expansion tanks get really expensive for the large ones, and a bladder type expansion tank is physically a large unit, much bigger than it's "acceptance volume" due to the need for the bladder chamber. Again for a pressurised unit, you are talking around the size of a typical large family hot water heater... The expansion tanks are normally located near the boiler, so they are in relatively "prime real estate" - the tall pipe tank in the attic is less likely to be using high value space...

From a functional standpoint, there is very little to go wrong with the tank in the attic, beyond the ever-present but relatively remote possibility of a leak - otherwise it's straight plumbing, operating by the laws of physics. Expansion tanks are slightly more problematic as they have a rubber bladder in them, which has been known to fail...

As mentioned, the "tank in the attic" may be easier to get past the code officials.

Essentially each approach has its own strengths and weaknesses - I would say that each person needs to evaluate their own situation and decide which is best for their circumstances, there isn't really a "best" answer...

Gooserider

 

[pybyr]

When I was still considering pressurized storage (before concluding that I could not find any suitable pressure-capable tank of decent size that could be shoehorned down my cellar hatch) I was considering the "tall pipe/ open tank above" approach being discussed here.

One thing that became apparent as important to consider (in addition to a piped overflow at the top of the upper vessel) was the sheer weight.

Let's say you need to make room for 60 gallons of expansion-- since water weighs roughly 8.34 pounds per gallon, that's 500 pounds of weight, concentrated in a relatively small footprint-- make sure that the upper portion of the structure, where the expansion tank is to be located, is suited to carrying that load.

 

[DaveBP]

Essentially each approach has its own strengths and weaknesses - I would say that each person needs to evaluate their own situation and decide which is best for their circumstances, there isn’t really a “best” answer…
Gooserider

That could be a "sticky" in itself to apply to a number of different elements of wood boiler systems.

 

[Singed Eyebrows]

Hi Outlaw; Sorry I didn't see your question earlier. Atmos requires a 500 liter expansion tank as the minimum size. They claim it is needed for power balancing. I bought a new Amtrol ASME 500L 175 psi for $500.00 off Ebay delivered to Mil. Wis. This is a $7000.00 tank so I was happy to pay this for it. If there is a real cheap way out on a tank I didn't find it, Randy

 

[Hansson]

I have 500 gallon storage tank and my semi open system have a 40 gallon expansion tank on the of the house.
Found a pic of a installation.Not my
(broken link removed to http://www.forumbilder.se/images/18112009103138c88f.jpg)

 

[RobC]

There is another way that doesn't get much attention that I will be trying shorty that other have had success with. Take an appropriate sized tank for expansion. My case I'm adding expansion for 1000G pressurized storage. I will try using a 100 Gallon ( NOT to be confused with a 100 pound ) propane tank. Add a fitting to the bottom of tank, drill and tap, or weld, for water inlet. Add a inflation nipple, Schrader valve, to the top. Hope fully I will be finishing my storage this week and will report back. If others have any feed back on doing this set up I would like to hear more. My supply and return run over head and the tank will be sitting on the floor, but, apparently, once you have the right amount of water in the bottom of the tank and air pressure in the top your good. You need to make sure that at cool temps you maintain water in the bottom of the tank.
Rob

 

[Singed Eyebrows]

Hi Rob & Hannson; These will work, you will get oxygen separating out into the system from what I have read here on Hearth. As Rob says too, you need to keep the proper water levels, something you don't need to worry about with a bladder tank. Nofossils suggestion sounds like the next best way to go(sounds like Hannson's setup) & if you float some oil/sealer on the water it's pretty much sealed, Randy

 

[leaddog]

I'm using a 250gal propane tank for expansion with my 2200gals closed system and doing as Rob says. I haven't had to add ANY air and it's been running a year. So very little if any O2 getting in system. It's setting on the floor vertical next to my boiler. I come off the bottem to the return side of the boiler and I don't even have it insulated as I get very little heat into the tank.
Leaddog

 

[Nofossil]

Another thing to consider with the semi-pressurized option is that expansion has to be sized for the worst-case variation in system volume (36 degrees to 250 degrees temperature swing). However, in real life the actual temperature swings are MUCH smaller. It's not as though you're moving 80 gallons in and out of your expansion tank every day. I suspect that even without an oil film, the dissolved oxygen in an open attic expansion tank wouldn't get down into the boiler very much at all.

Despite repeated threats, I haven't had time to design and document my current thinking on the 'ultimate' heating system. I'm leaning towards pressurized storage and an open expansion tank in the attic. One of the reasons is that I'm one of the people who run with my makeup water turned off so that any leak will be immediately apparent (due to pressure drop) and will NOT result in a flood or hidden damp spot that persists for years until a section of the house falls off.

With my makeup water disconnected, low pressure is my only warning, and that will cause my backup heat to NOT operate. With attic expansion, I could have a level sensor (think sump pump float switch) that would let me know that I'd lost water while there's still plenty to provide operable system pressure.

I think I'd build a small (4' x 6') insulated room in the attic with an access hatch to the room below. The access hatch would have to be designed to lose just enough heat to keep the attic room above freezing.

 

[rkusek]

How much water did you add to the 250gal tank? What is the "effective" expansion size now? I will have 700' of 1.5" buried Pex rising to a point in the home about 20' above where the boiler is located downhill in the shed. If I have 1000 gals of storage next to the boiler I think I will need to go with a similar size expansion since a bladder type would be rather expensive. NoFossil, I was wondering if anyone had tried the following for makeup water rather than a direct connection to the rural water system. What if I took a ~50-80 gal plastic tank and used an RV type pump/pressure switch. I would have to check but I believe they maintain something close to the 12 psi range. Wouldn't a check valve prevent 190* water from getting back into the pump since I'm sure it couldn't handle high temperature? A clear tank near the boiler would allow me to see if the level was dropping due to a leak, etc. The RV pumps are 12V and could be connected to the battery backup for the boiler. We lived in a RV for a year and the pump seemed pretty durable in my opinion since it ran so frequently. I could also have a float switch in the plastic tank to indicate a low water condition like you mentioned as well.

 

[Nofossil]

How much water did you add to the 250gal tank? What is the "effective" expansion size now? I will have 700' of 1.5" buried Pex rising to a point in the home about 20' above where the boiler is located downhill in the shed. If I have 1000 gals of storage next to the boiler I think I will need to go with a similar size expansion since a bladder type would be rather expensive. NoFossil, I was wondering if anyone had tried the following for makeup water rather than a direct connection to the rural water system. What if I took a ~50-80 gal plastic tank and used an RV type pump/pressure switch. I would have to check but I believe they maintain something close to the 12 psi range. Wouldn't a check valve prevent 190* water from getting back into the pump since I'm sure it couldn't handle high temperature? A clear tank near the boiler would allow me to see if the level was dropping due to a leak, etc. The RV pumps are 12V and could be connected to the battery backup for the boiler. We lived in a RV for a year and the pump seemed pretty durable in my opinion since it ran so frequently. I could also have a float switch in the plastic tank to indicate a low water condition like you mentioned as well.

The check valve would be a no-no, since water has to flow into and out of the expansion tank as the system temperature changes. In this scheme, the expansion tank is NOT pressurized - it's open to atmosphere.

If what you're suggesting is a stand-alone makeup water supply system, that's certainly possible but seems like overkill. If you don't have leaks, you don't need makeup water.

The semi-pressurized approach depends on having the open expansion tank at the highest point in the system, and high enough above the boiler to provide acceptable pressure. If your plastic tank is to be used as an expansion tank, I'd be uncomfortable with it being pressurized because if you have an unexpected flow problem and boil the water in your system the pressure will reach the blowoff valve pressure - usually 30 psi.

 

[rkusek]

[quote author="nofossil" date="1255380197The check valve would be a no-no, since water has to flow into and out of the expansion tank as the system temperature changes. In this scheme, the expansion tank is NOT pressurized - it's open to atmosphere.

If what you're suggesting is a stand-alone makeup water supply system, that's certainly possible but seems like overkill. If you don't have leaks, you don't need makeup water.

The semi-pressurized approach depends on having the open expansion tank at the highest point in the system, and high enough above the boiler to provide acceptable pressure. If your plastic tank is to be used as an expansion tank, I'd be uncomfortable with it being pressurized because if you have an unexpected flow problem and boil the water in your system the pressure will reach the blowoff valve pressure - usually 30 psi.[/quote]

I may haven not been clear on my last post. I was asking about 2 separate issues, the expansion system of Rob C & leaddog and make up water options. They are using a 3rd expansion option that I had not read about. Using a smaller propane tank (100-250gal) partially filled with water, a pipe fitting on the bottom, and charging it to 12 psi with a Schrader valve on top. I had been leaning toward the bladder tanks but I'm sure I would need over 100 gal which looks like it could cost a bundle. The semi open is not really an option since I have no where near the 33' required.

I agree with you on the make up water not being necessary for the most part. The check valve would go between the boiler and the RV pump connected to the plastic "make up" water tank to prevent pushing 200* water back into the RV pump and probably damaging it. I was thinking of the condition where the boiler circ failed with a full load of wood which I believe happened to someone last year. I guess the overheat loop with an aquastat connected to the automag should cover this condition.

 

[sdrobertson]

This is the expansion tank I'm using. I think its 330 gallons and it's off a field sprayer. It's just like a propane tank and I just ran a line from the bottom into my boiler line. The amount of water in the tank goes up and down approximately 12"s when I change from 125 degrees to 190 degrees. I have not added any air to this and I'm in my second year.

 

[rkusek]

This is the expansion tank I'm using. I think its 330 gallons and it's off a field sprayer. It's just like a propane tank and I just ran a line from the bottom into my boiler line. The amount of water in the tank goes up and down approximately 12"s when I change from 125 degrees to 190 degrees. I have not added any air to this and I'm in my second year.

That picture is deceiving. That green tank looks more like about 80-100 at most. Nevertheless are you saying it is about 1/3 full of water (110 gals) and then has about 220 gals of air for expansion? This would be about 10% of your total storage which sounds about right from what I've read here. Hot Rod had a post awhile back that looked like a Windows program to calculate expansion needs taking piping volume and height into account. 10% sounds safe though, so about a 150-250 gal tank is what I need to find. How are you seeing the level in the tank change? It sounds like the oil film is unnecessary.

 

[Jeff S]

This is the expansion tank I'm using. I think its 330 gallons and it's off a field sprayer. It's just like a propane tank and I just ran a line from the bottom into my boiler line. The amount of water in the tank goes up and down approximately 12"s when I change from 125 degrees to 190 degrees. I have not added any air to this and I'm in my second year.

How do you initially set this type of system up?Do you add air to the expansion tank or do you simply just add the tank once the rest off the system is full ?Do you have a make up water system also? Thanks Jeff.

 

[leaddog]

The propane tanks and anhydrus tank that sdrobertson is using have fuel gages that we are useing to give the water level. I had to turn them 90* and adj the arms as they were for horizonal use but they work well and they were there. They work well for expansion tanks as they are pressure tanks, and the metal is thick enough so you just have to tap a 1/8 pipe tap in the to for a air valve and a 3/8 pipe tap in the bottem for a 3/8pipex1/2pex fitting and you are good to go. Just connect it into the return line before to pump. We haven't insulated them as there is very little heat lost as the water moves very slowly and there isn't much movement of water when you keep a fire going. We first thought we would charge them with nitrogen but we haven't had to add any air so there seems to be VERY little o2 desoving into the water.
The main problem is finding the tanks as they are in very high demand to make OWB with. People are putting them inside 500gal tanks as fire boxes. The ones I was able to find went as much as 500gal ones. and I can't get any more. I do have one 300gal one but it is 10ft long.
This system was used on well systems for years before the bladder tanks came into being but you had to add air often, but that was because you were adding and removeing water all the time. Here you are leaving the same water in the tank and it is just going up and down slightly so the air isn't being desolved into the water. Works for me
leaddog