Storage Quantity

[chuck172]

I have a TarmSolo 40 with 500 gallons of pressurized storage, (propane tank) . I really can't heat the house, HW, and bring the tank up to temp. for 24 hrs with one firing.
Thinking about increasing the storage to 1000 gallons.
Thinking again, what will I gain? I really don't mind starting the boiler up, kinda like it. I have all the time in the world to tend to it.
Increasing my storage will not make my system any more efficient, I won't burn any less wood will I? My system barely- if ever -idles now!
It would take me twice as long to build up 1000 gallons to 85* as it would 500 gallons.
My system works great. No ghost flows, I'm installing a Tekmar 156 control this week to really simplify charging the tank.
Besides the convenience of less stops and starts, is there any real advantage to "more" storage?

 

[sdrobertson]

My system works great. No ghost flows, I'm installing a Tekmar 156 control this week to really simplify charging the tank.
Besides the convenience of less stops and starts, is there any real advantage to "more" storage?

If your not idling much and don't have a problem with firing like you are now, I would say that there would really be no benefit to adding more storage. The real advantage is time. I work 12 hour days so I'm gone for 14 hours when I have to work so I wanted allot of gallons to get me through when I'm not able to feed the boiler. I haven't done it yet but I should be able to go over 24 hours without a fire if I had to-allot longer if I turned the house temp down from 76 degrees if I was going away for a while.

 

[DaveBP]

If your system isn't idling and you and the system have a routine you enjoy, you are sitting pretty. More storage will only give you more heat storage. That just means longer time between burns. It could make a difference when the bitterest coldest nights come along then you might need to get down to the boiler sooner than your accustomed to and maybe when you want to get away for an overnighter somewhere out of town.

Let us know how the Tekmar 156 works and how you installed it. I'm and several others are very interested.

 

[chuck172]

I think many readers on this forum especially those new to wood-boilers feel that more storage = more efficiency = less wood used. That's not necessarily true. Adding more storage in many cases, can be a royal pain in the a**.

 

[sdrobertson]

I think many readers on this forum especially those new to wood-boilers feel that more storage = more efficiency = less wood used. That's not necessarily true. Adding more storage in many cases, can be a royal pain in the a**.

I agree that it can be a pain - and I think the efficiency gain is minimal as nofossil's data has proven - storage is just a battery, the more battery you have, the longer between burns up to a point as you have to consider standby losses and where these losses go to.

 

[WoodNotOil]

Another point that may be worth making is that it takes a longer burn to charge more storage. That may end up being less convenient for you. Devising a way to have two separate 500 gallon storage tanks that could be charged/discharged separately may be an interesting solution. Not sure if anyone has done that or not. . .

 

[sdrobertson]

Another point that may be worth making is that it takes a longer burn to charge more storage. That may end up being less convenient for you. Devising a way to have two separate 500 gallon storage tanks that could be charged/discharged separately may be an interesting solution. Not sure if anyone has done that or not. . .

What advantage would this be? I can isolate my four tanks easily with shutoffs off my manifold but I haven't done this but I could to test something. I just don't know what I would test.

 

[taxidermist]

I have 1000 gal of storage and right now I am burning for about 8hr a day and I can run my tanks to 180 and when I get up at 6:00(no over night fire) am my tanks are around 140 to 150 depending on the over night outside temp. I have a 60 but have it throttled back to 1 nozzle 50-60 on fan speed 38 to 1 inch on fan shutter, primary at 1 inch, sec. 2 turns. That is this week as we know things change.

Rob

 

[DaveBP]

it takes a longer burn to charge more storage

You don't need to let your storage cool down all the way each time.

Take it to the absurd extreme; say you had 20,000 gallons storage. You don't need to run it down to whatever minimum you can use and then burn for 43 straight hour to get it back up to your maximum. You could just do your once a day burn routine between 180 and 178 say, and life would be about the same as when you had 500 gallons. But suddenly you win an all expenses paid 4 day trip for two to Iceland in January! How can you pass up an opportunity like that? No problem. You just use your storage to the max and go.

OK, maybe not the most likely scenario. Just beating the point to death that once you have enough storage to keep your boiler from idling, the main advantage of more storage volume is convenience, not more efficiency. If your storage is outside the standby losses might even make it less efficient, if your storage is inside your heated space it's a wash.

 

[WoodNotOil]

it takes a longer burn to charge more storage

You don't need to let your storage cool down all the way each time.

Take it to the absurd extreme; say you had 20,000 gallons storage. You don't need to run it down to whatever minimum you can use and then burn for 43 straight hour to get it back up to your maximum. You could just do your once a day burn routine between 180 and 178 say, and life would be about the same as when you had 500 gallons. But suddenly you win an all expenses paid 4 day trip for two to Iceland in January! How can you pass up an opportunity like that? No problem. You just use your storage to the max and go.

OK, maybe not the most likely scenario. Just beating the point to death that once you have enough storage to keep your boiler from idling, the main advantage of more storage volume is convenience, not more efficiency. If your storage is outside the standby losses might even make it less efficient, if your storage is inside your heated space it's a wash.

I see your point. Just don't let it get down quite as far in temp. Makes sense

I was merely thinking aloud. My thought was that one 1000 gallon tank and two 500s could perhaps operate differently. If you charged one at a time, you could have hotter usuable water sooner from one tank versus bring the entire 1000 gallons up at once. It would kind of be an extension of the stratification in effect. I think you may see hotter usuable temps that way versus one tank. However, a well designed system that can heat effectively in the 140-180*+ range wouldn't necessarily benefit from hotter usuable temp. Still just thinking here. . .

 

[free75degrees]

I have 800 gallons unpressurized now and my feeling is that more storage would mean that I wouldn't have to plan as carefully. I have two 8 hours stretches where I can't tend to the fire - while I'm at work and at night. My tank needs to get me through these stretches. Even in the coldest temps we have had this winter the 800 gallons has done fine, as long as the tank is near 180 at the beginning of the 8 hour stretch. It gets tricky when it is a little warmer and the tank is not at full temp. I often decide to skip a fire if the weather forecast and tank temp are such that I might get through the next 8 hours with the heat in the tank. A few times I have guessed wrong and the oil has kicked in for short periods before I was able to get a fire going when I got home. If I had a larger tank these decisions would be much easier because I would be able to ensure that there is always enough energy to last for significantly longer than my 8 hours away. If you don't have extended times where you are away from the house, then larger storage probably does not make sense. I guess one can think of storage in 2 ways: a means to prevent idling, and a means to heat the house when there is not a fire going. 500 gallons sounds like it is just enough for the first purpose. Any more would just serve the second purpose.

 

[DaveBP]

one 1000 gallon tank and two 500s could perhaps operate differently.

I have 2 500's sitting out by the barn in the snow myself at the moment. And exactly the same thing is hovering around the edge of my mind, too. I've worked through half a dozen ways to hook them together but I also want to do it so I can add some new configuration that I or others come up with. The KISS principle keeps popping back into my mind so I just keep watching this forum for ideas and biding my time and trying not to get too carried away and over-complicating it.

Lot of posters here looking for a rule-of-thumb on optimum storage size but the fact is there just is no way to sum it up so simply. The variables are just too wildly diverse. Are you heating a drafty old farmhouse with baseboards that need high temp water to run well? Do you have a new, well insulated passive solar airtight home that can easily heat on the coldest day with 100F water in its radiant floors?
They vary not only in how much wood it will take to keep them warm but I think also in how best to use that wood. Each situation will have a different 'best' system.

Now, if I can only convince myself that I have "my best" setup when I start to install it.

 

[flyingcow]

I have 800 gallons unpressurized now and my feeling is that more storage would mean that I wouldn't have to plan as carefully. I have two 8 hours stretches where I can't tend to the fire - while I'm at work and at night. My tank needs to get me through these stretches. Even in the coldest temps we have had this winter the 800 gallons has done fine, as long as the tank is near 180 at the beginning of the 8 hour stretch. It gets tricky when it is a little warmer and the tank is not at full temp. I often decide to skip a fire if the weather forecast and tank temp are such that I might get through the next 8 hours with the heat in the tank. A few times I have guessed wrong and the oil has kicked in for short periods before I was able to get a fire going when I got home. If I had a larger tank these decisions would be much easier because I would be able to ensure that there is always enough energy to last for significantly longer than my 8 hours away. If you don't have extended times where you are away from the house, then larger storage probably does not make sense. I guess one can think of storage in 2 ways: a means to prevent idling, and a means to heat the house when there is not a fire going. 500 gallons sounds like it is just enough for the first purpose. Any more would just serve the second purpose.

Build a smaller fire to get thru the tricky times. If you have your dump zone hooked up right worse thing that'll happen is it'll run warm a little while.

 

[steam man]

Everyone makes good points here. I am leaning towards a smaller tank but also using a low temperature radiant setup. Just using a lower temp heat load obviously will increase the useable btu storage capacity. Another variable to think about since two different systems with tanks exactly the same size with the same heat load may not have the same useable storage capacity. A btu is a btu at 100 or 180 deg.

Mike

 

[Duetech]

Not that I am at that "I have storage" point yet but it seems the storage talk, at the moment, is only concerned with the current heating season. Not to differ with any point I would just like to add that some of us maintain dhw throughout the year and storage burn cycles can get up to once in 7-10 days apart. One good fire at that rate would be very efficient for me. As it is I have to run a daily small fire for dhw purposes, about a half load per day. Being able to do one burn even for three days would be a savings for me and would eliminate my creosote/idle concerns.

For the current season requirements if I can get down to 1 1/2 to one load per day with storage I would be doing well again as the burn/idle cycle I have to maintain requires two loads per day and it is probably fair to say that once up to temperature that up to 50% of my wood is burned at idle.

Even so at today's lower fuel prices I am able to burn wood cheaper than what it costs for petroleum products. This thread, though, has opened up consideration to a less strenuously built storage tank system. Thanks to you all for your input...Cave2k

 

[DaveBP]

the storage talk, at the moment, is only concerned with the current heating season

Well, it is easy to get caught up in the heat of the moment...

Year 'round DHW is a powerful argument for storage. And I suppose this coming summer it will be the major topic for the storage issue. I have always burned wood so I have no history of fuel bills to look back to but I remember it was seeing a friend of mine heat water for showers for a houseful of college students with a Tarm and storage in July that made me say to myself "I want one of those".

 

[WoodNotOil]

Year 'round DHW is a powerful argument for storage.

That is why I put my storage in last summer. I burn every 6-9 days in the summer depending on demand.