# How much water storage do I really need?



## Shawn Straffin (Jul 26, 2011)

I have a 1800 sq ft log house with Eko 40 in Garage ready to install. The only information I can find in these threads is people going bigger and bigger with their water storage. I have a Burghman oil furnace/boiler in tandem with my system. That seems to do fine with my 50 gallon hot water storage tank. I'm having trouble fully grasping why I would need more than 500 gallons of water storage? 
Also what is the best manner of storage tank? The more inexpensive and ingenious the better.


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## Clarkbug (Jul 26, 2011)

You will probably get a lot of different replies about storage, and there is plenty of good reading here.  Depending on the manufacturer, they have a rule of thumb regarding the gallons of storage per btu/h output for a boiler.  I dont know if Eko has one or not, someone on here should have a good answer for you.

Essentially, storage allows you flexibility on when you have to burn, not how much you have to burn for the season.  And is your 50 gallon tank for domestic?  The majority of the tanks discussed here are the heating hot water storage tanks, not the domestic hot water storage.  

"Best" tank is again subjective, and really depends on a number of factors.  Lots of folks go with used propane tanks, but there can be availability issues, as well as access to get them into your basement or outbuilding. Several people here have built their own unpressurized tanks out of plywood and put an EPDM pond liner in them, and used coiled copper tubing as a heat exchanger.  Pressurized storage allows you to heat the water up to a higher temp, but requires an expansion tank.  Lots of good info here!


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## Shawn Straffin (Jul 26, 2011)

I'm also still curious about the pressurized and non pressurized water storage. Further, will a couple of insulated 275 gal oil tanks be strong enough to hold the pressure I need? Is pressurized water storage my only option?


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## jebatty (Jul 26, 2011)

A main reason storage is useful with wood boiler hot water heating is that, as opposed to your oil boiler which can turn itself full "on" in seconds and then full "off," a wood boiler has a load of wood to burn whether or not your system needs the heat. The btu's from that burning wood have to go somewhere, and a storage tank is an ideal place to put them. The wood boiler too can shut down, but the shut down is slower than with the oil boiler, and the wood boiler too can restart, ditto. But unlike the oil boiler that efficiently starts up and shuts down by controlling the fuel supply, the wood boiler does the same by controlling the air supply. That is inefficient at best and increases emissions in the start and stop cycles. Ideally, wood burns best when it burns without interruption from start to finish under the controlled air conditions of your Eko.

There is no single answer to how much storage you "need." I  believe your Eko is designed to work with no storage, with inefficiencies. So you don't need any storage. The next level of "need" is enough storage to handle the excess btu's from a load of burning wood. You can control that to a considerable extent, and therefore have minimal storage, by timing and sizing your wood loads to more accurately supply only the heat you need, with the minimal excess then going to storage. But that also will require more frequent tending and monitoring the wood boiler operation, which greatly will depend on heat demand, outside temperature, etc. Not the most convenient but very workable. 

Maybe the highest level of reasonable "need" is as large as could handle the btu's from a burn of a full load of wood with no demand from your system. Let's say that is 100 lbs. of wood, which is about 500,000 btu's (6050 btu/lb at 20% MC, 400F stack temp, and 85% efficiency for the boiler). If your minimum useful system temperature is 150F, and your boiler is capable of 190F output, then 1500 gallons of water could handle that (1500 gal x 8.34 lb/gal x 40 delta-T). 1500 gal is probably more than most users with storage have.

Need then also relates to how long you want to be able to provide btu's from storage to meet system demand between boiler firings. To deal with this you need to know your heat loss, that is, how much heat you need to maintain the interior temperature you want for comfort. You need to do a heat loss calculation to determine this, or estimate it from experience. Let's say that is 50,000 btuH. In the last example, with 500,000 btu's stored and heat loss at 50,000 btuH, storage could provide 10 hours of heat before the boiler would need to be fired again.

Although this is complicated at the extreme, others users can chime in with their practical experience and provide a user's guide as to the amount of useful storage for an Eko 40. I have a Tarm Solo 40 (140,000 btuh rated output) and have 1000 gal of pressurized storage. Works very well in my situation with heat loss maximum at about 20,000 btuh and minimum usable temperature of 100F, and I can store 750,000 usable btu's.

No - you cannot use oil storage tanks for pressurized storage. Don't try it. 

I assume your current oil boiler system is pressurized, the Eko 40 is pressurized, and I would recommend staying with pressurized storage if at all possible. In my mind this is simpler and more efficient, but also due to space considerations doesn't work well for many people. 

Others will have more to add. Enjoy your system. Don't fret too much.


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## jimbom (Jul 26, 2011)

JeBatty - an excellent summary of this topic.


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## Shawn Straffin (Jul 26, 2011)

Happy to be here, thank you for the support, its coming much clearer. 

With the price of steel large propane tanks are getting rarer than hens teeth, and demanding a premium when you do find them.
Are these recommended?
I see New Horizons want $2500 or so for their pressurized storage... 
That would hurt...


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## woodsmaster (Jul 26, 2011)

Eco-Worx said:
			
		

> Happy to be here, thank you for the support, its coming much clearer.
> 
> With the price of steel large propane tanks are getting rarer than hens teeth, and demanding a premium when you do find them.
> Are these recommended?
> ...



Do you have to have the certifacation tag on a psessure vessle where you live ? If not you should be able to find decommisioned 500 gallon propane tanks for $200 - $300. Then add a
hundred or two to have fittings welded on etc. I think 500 gallon woulb be a good fit for a eko 40 ,but it just depends on your needs.


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## willworkforwood (Jul 27, 2011)

woodsmaster said:
			
		

> I think 500 gallon would be a good fit for a eko 40 ,but it just depends on your needs.


Not trying to be disagreeable here, but I remember another member posting multiple times expressing disappointment with his 500 gallon storage. I don't recall which gasser, and believe he has BB emitters. His feeling was that he needed more, and wasn't in a situation to add at that time.  Now that's just one case, and maybe if others have 500 gallons and are happy with that (or know of others who are), perhaps they will post their experience.  Not claiming any expertise here (no storage :lol: ), and not saying you're wrong about the 500 gallons - just passing along one persons story.


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## Duetech (Jul 27, 2011)

The "needs" is the qualifier in woodmaster's humble but qualified equation. 500 works for some but heat loads of two homes of the same size can vary tremendously because of design and insulation and etc. etc. etc. even elevation in the same basic locale and what willwork forwood points out reflects that. Jebatty points out that you need to know your heat load requirements and knowing that means you can determine how many stored btu's you need and the storage you need to handle the load. How that is achieved mechanically is part of the equation. How you are able to represent yourself with that mechanical knowldge can influence your choices dramatically. In a gasser dry wood is not an option. It is a must! Smaller storage requires less immediate attention and larger storage requires you attend the burn time required to achieve the needed stored btu's. Your lifestyle will dictate a lot about your system design. Controllers will allow you to bypass the boiler when it shuts down so it doesn't rob btus from storage while awaitng the next burn cycle.The simple answer is start designing your system and ask all the questions you can but use a pencil with a good eraser and sooner or later the simplest custom design will find its way to the paper. My EKO40 saved me thousands in fuel oil and dhw costs without storage. 

Jebatty advises you well DO NOT USE FUEL OIL DRUMS FOR PRESSURIZED STORAGE. One rupture at 180*f could easily be a fatality or more. On the other hand coiled copper tubing submerged in lined drums or one larger combined drum would allow you to have pressure in the tubing and greatly reduce a risk of a tank rupturing. all storage tanks need to be insulated.


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## jebatty (Jul 27, 2011)

Many variables are involved in determining "needed" storage. Three key ones are storage volume, minimum reasonable usable temperature (MRUT, for short in this post), and heat load, and all of these are importantly related. If your MRUT is 180F, as it could be for baseboard, then it will be difficult for nearly any amount of storage to do more than serve as a buffer to take just a little of boiler output beyond need and provide a small storage to meet heat demand.

Example #1: 1000 gal of storage, boiler output maximum 190F, MRUT of 180F. Maximum available stored btu's = 1000 x 8.34 x 10 = 83400. If your heat load is 50,000 btuH, then your storage will serve only to buffer a little excess output from the boiler and then provide needed heat for 83400/50,000 = 1.67 = 1:40 hours.

If, however, you have radiant infloor or possibly panels where MRUT = 100F, then storage volume is a huge factor in helping you decide how much storage you need.

Example #1: 1000 gal of storage, boiler output maximum 190F, MRUT of 100F. Maximum available stored btu's = 1000 x 8.34 x 100 = 834000. If your heat load is 50,000 btuH, then your storage will serve only to buffer considerable excess output from the boiler and then provide needed heat for 834000/50,000 = 16.7 = 16:42 hours.

In both examples, if your heat load was 25,000 btuH, then double the times in the examples, or if was 100,000 btuH, then halve the times. 

These examples also show how important it is to minimize your heat demand, such as through insulation, crack sealing and other inexpensive energy savers. Do all of these first, do them with the new boiler, but just do them. There is no better or cheaper way to improve heating system performance than through these energy savers.

One other point. If you have an existing heating system, I assume you will retain it for backup heat. And I then would not plan the wood boiler to provide all the needed heat at low temperature extreme. For example, if average low temperature is 0F, which is about what it is where I live, but extreme low temperature is about -35F, I would plan the wood boiler to handle the heat load down to about 0F, give or take, and use the existing system to provide the boost on those extra cold days. This also helps in determining the amount of "needed" storage, as a system which requires 180F at the temperature extreme may only require 160F or less at average or less extreme temperatures.


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## flyingcow (Jul 30, 2011)

Heat load calc?


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## Rory (Jul 31, 2011)

I have unpressurized storage and am completely satisfied with it.  My home built "tank" is 4x4x8, and I think I calculated it out to around 670 gallons.  My house is 2500 sq ft (not counting the cellar), and I wish the storage was just a wee bit larger, so I think what I have would be ideal for an 1800 sq ft house.


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## stee6043 (Jul 31, 2011)

I personally would not be heating with wood if I did not have 1,000 gallons of storage (pressurized).  I heat 3200 sq.ft. with an average heat load of 25,000btu/hr +/-.  I start a fire after dinner each night to charge storage and heat the house.  It burns until after midnight each night after I go to bed.  I heat from storage 100% after the fire burns out until I get home from work again the next day.

  Anything less than 1,000 gallons would not work for my situation.  Nor would unpressurized storage of this volume.

  I've never heard anyone on this site say "I wish I had less storage".  I've heard multiple people on this site say "I wish I had a little more storage".


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## Shawn Straffin (Aug 1, 2011)

Why would un-pressurized storage at that volume not work for you stee6043?
I have not decided on either pressurized or not. 
Pressurized seems more practical, purely because the lack of need for heat exchanger. Exchange also equates to at least a little loss in my mind?
However, pressurized seems to have added danger and greater, possibility of leakage and failure.
Not to mention the expense.
If its worth it, its worth it....
I just need to know the how's and why's.


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## flyingcow (Aug 1, 2011)

Eco-Worx said:
			
		

> Why would un-pressurized storage at that volume not work for you stee6043?
> I have not decided on either pressurized or not.
> Pressurized seems more practical, purely because the lack of need for heat exchanger. Exchange also equates to at least a little loss in my mind?
> However, pressurized seems to have added danger and greater, possibility of leakage and failure.
> ...



Same thoughts i had when doing my system. I went with unpressurized because of expense and it works better for summer DHW. Plus the tank i have fits in the basement. Works very well.....but i tend not to overthink things. Which is not meant to be a slight to anyone. If you knew me, I can't over think things. Don't have the tools?


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## stee6043 (Aug 1, 2011)

Eco-Worx said:
			
		

> Why would un-pressurized storage at that volume not work for you stee6043?
> I have not decided on either pressurized or not.
> Pressurized seems more practical, purely because the lack of need for heat exchanger. Exchange also equates to at least a little loss in my mind?
> However, pressurized seems to have added danger and greater, possibility of leakage and failure.
> ...



Typically you can't go as high or low with storage temps in a non-pressurized setup.  You have the inefficiencies of an additional HX to take into consideration.  I rely on maxing out my storage to 185 +/- each night and bringing it all the way down to 140 (sometimes lower) before I start the next fire.  Overall, and some may disagree, I don't think you can get the same responsiveness and performance in this broad a range with non-pressurized tanks.

It's all about the trade-offs.  Non-pressurized tanks are much easier to work with and many times can be home built.  Many municipalities also require a system to run at atmospheric pressure.  Pressurized tanks are cheap, somewhat challenging to get into a basement and require just the right inspector (or setup) to get approval.  I consider myself fortunate to have the room for propane tanks, had a source for new tanks and managed to get them approved/insured without any trouble.


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## tom in maine (Aug 1, 2011)

As one who has done a few unpressurized tanks in his time, I thought I should add my 2 cents in.

Using a heat exchanger is not going to create that much of a difference in the thermal capacity of any system. It will add some additional time to pump operation, to compensate for not being 100% efficient.
If you consider a hx at 85% (we seem to be in the 90's with ours), then a circulator might run 15% longer than without a hx. The energy is not lost, it just will take longer to get into the system.

There is no reason that you have to use a HX since many systems can operate unpressurized. I use all non-ferrous pumps and fittings and eliminate the heat exchanger on the heating loop (this is with a stainless steel boiler). Water can be treated with steel or cast iron boilers. Of course, you need to be diligent about water treatment in that situation. 
I think if the system needs to be pressurized, a HX is not big investment over making sure that the boiler chemistry for 1,000 gallons of tank/boiler water is right.

The other alternative is plate heat exchangers. They are usually less expensive, but do require another circulator.

We use a single heat exchanger to interface the boiler with the tank and heating system when the system is pressurized.

We do use a liner that is spec'ed to 200F continuous. This eliminates some of the issues with EPDM and even high temperature PVC tanks storage capacities.


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## thehaas (Aug 2, 2011)

storage is built into wood coal boiler design.my d.s.machine boiler holds 85gallons water .has no problem heating baseboard i have in each room.my dump zone is 6 cast iron radiators that only purpose is for when boiler high temp is reached and cold water from dump zone radiators circulates into boiler to bring temp down .also could just have steel box welded in stead of radiators.dump zone should be minimum half boiler capacity boiler 85 dump around 40gal .these tanks with water in everyone talks about is like taking swimming pool and running pex lupe into and heat is released into pool of water.i try to keep it simple the dump zone loop i have has circulato and zone valve aquastat on boiler when up to 200 turns on


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## thehaas (Aug 2, 2011)

i made some videos with my boiler after mant trial runs you can watch on you tube bodyshop18336  this is a pressure system like home boiler


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## Badfish740 (Aug 2, 2011)

I'm debating this one right now-if you read my thread about installing a hot water heat system from scratch you'll see what I'm working with.  Basically I'm looking at adding just shy of 400 SF to my home with a full basement underneath.  That would give me ample room for both boilers, storage, and plenty of room for wood.  I don't have a lot of experience with the code inspector around here-he did approve my wood furnace install without fuss (I had diagrams prepared showing I had increased minimum clearances by a factor of 3, etc...he glanced it, signed the approval, and handed it to me in less than 2 minutes), but I'm worried that the words "pressurized system" and "self installation" will set off alarm bells.  I know that I can do this myself, don't have the money to pay someone else to do it, and even if I did, I'm betting I'd have a hard time finding a plumber willing to do the job in this litigious state that probably doesn't have near as many folks running these system as New England and the Upper Midwest.  That being said, I'm seriously considering constructing some sort of 1000 gallon unpressurized tank as part of the new basement space.  The other motivating factor is wanting to incorporate these home built solar collectors into the system:

http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm 

I might as well put the direct southern exposure with no tree cover that makes my house hell to air condition to good use!  Finally, I know someone alluded to it earlier, but is there a thread that details the corrosion issue thoroughly that someone can recommend?  I know it's a problem, but I don't know much about how to deal with it-if someone could explain that I'd be grateful.


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## Shawn Straffin (Dec 8, 2011)

Have a neighbor, just bought a Eko Bio-Mass 60... Doesn't seem to be re-ignighting for him after a couple hours. He's dumpin heat to beat hell with a Modine on his return side. So I would think it would be calling for heat quicker than it is. Also female connections on the back of the controller seem to have fallen off and are loose to the male connections? 
Anybody else have trouble with it coming back to life after a couple of hours?

Thanks


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## henfruit (Dec 8, 2011)

Is it an EKO or a biomass?


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## stee6043 (Dec 8, 2011)

What do you mean "coming back to life"?  If the fire goes out, it's out. There is no "reigniting" automatically.


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## maple1 (Dec 8, 2011)

But if it idles for 2 hours, is it really out?


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## Shawn Straffin (Dec 8, 2011)

Bio mass 60 , anyway when unit shuts down, how long do coals generally last before there is no hope of fans bringing coals "back to life" or back to the point where there is enough heat for gasification?


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## mwk1000 (Dec 9, 2011)

> I rely on maxing out my storage to 185 +/- each night and bringing it all the way down to 140 (sometimes lower) before I start the next fire.  Overall, and some may disagree, I donâ€™t think you can get the same responsiveness and performance in this broad a range with non-pressurized tanks.



That is 45 degrees * weight of water in your tank. Each situation is different, I have an open tank I use from 170-110 for 60 Degrees * my water mass. It heats just fine. I have the EDPM with a plate HX external.

I used a spreadsheet when figuring out how big with just the information the guys here are talking about. 
1) Usable heat range for YOUR home, radiant ? Forced Air, etc.
2) Burn time needed to charge the tank to "full" This is where larger is not allays better. And a reasonable estimate of your boilers output is needed.
3) # of hours you want to run before burning again. ( This requires knowing your heat load ) I was aiming for one burn per day on the coldest day.
I balanced these things and came up with how many BTU's I would need and then backed that into gallons of water and came out with 1500.


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