Boiler/Thermal Storage Expansion Tank Sizing

[DSSA]

I've picked up an older Eko 40 gasification wood boiler, an unused, 2024 production date, 1040 gallon, ASME certified (but I need to insulate) thermal reserve tank, an older 41 Gallon BoilerMate Indirect water heater, and am looking into expansion tanks so that I can start laying out my plans for installing this all.

I've been hearing/seeing that expansion tanks should be sized roughly 10% of the system volume, and understand that there are calculators out there for sizing them, but without knowing the delta temps at this point, nor exactly what volume will be with the lines running to the house from the detatched garage it will all be be housed in, I'm just going off of that "rule of thumb", which is telling me that I basically need a 150-200 gallon expansion tank, which is a hard find.

I have have some height in said garage (I believe it's almost 14' tall ceiling, and I do have a crawl space above it, although it's not an easy access), and see that mounting the expansion tank above it will lessen the size needed--is this correct? If so, by how much?

Is it also acceptable to run several smaller tanks in series-parallel?

Any other solutions to "skinning-the-cat" that I'm missing?

My plans are to hopefully batch-burn this boiler as opposed to letting it idle.

Thank you.

 

[hobbyheater]

My storage tank is 1040 imperial gallons and my expansion tank is a 40 gallon hot water tank ,works fine .

 

[DSSA]

My storage tank is 1040 imperial gallons and my expansion tank is a 40 gallon hot water tank ,works fine .

Is it mounted higher than your storage tank?

 

[salecker]

I have 1000 gallons and got the biggest one i could, i had to add the expansion tank that came with the boiler and it took acre of my issues of loosing a bit of water when i reached max temps, and would have to add a couple liters when it was cold.
Now i haven't added for a few years or had and loss of water.

 

[DSSA]

I have 1000 gallons and got the biggest one i could, i had to add the expansion tank that came with the boiler and it took acre of my issues of loosing a bit of water when i reached max temps, and would have to add a couple liters when it was cold.
Now i haven't added for a few years or had and loss of water.

What size is "the biggest one your could"?

 

[brenndatomu]

Our gas fired boiler (hydronic heater) system at work is supposedly 350 gallons, and the expansion tank is maybe 10 gallons...maybe. Been like that since 1969...works fine.

 

[DSSA]

Our gas fired boiler (hydronic heater) system at work is supposedly 350 gallons, and the expansion tank is maybe 10 gallons...maybe. Been like that since 1969...works fine.

Thanks, but that's a completely different beast. The unless the Delta T on that system is 100+ degrees. If I was letting the boiler idle, I'd probably be able to get away with something like 30-40 gallons, depending on what the system is set to kit on at. I'll be batch burning, so in the summer, or if I don't use it for a while and resort temporarily to heat pump/oil, the Delta T could be as high as 145 degrees or more.

If you're running a wood boiler constantly, or running a gas/oil boiler, and the water temp isn't swinging as much, you can get away with smaller expansion tank as the water volume isn't contracting/expanding as much. Still, I'm not seeing how the "10% rule-of-thumb" expansion tank thing is realistic. Maybe in case of an over-run condition and accounting for steam? You'd think that would be taken care of/safeguarded by the relief valve.

For example (assuming 1000 gallons, temps in Fahrenheit, and cubic feet of space):

Temp/Specific Volume
50 degrees/16.024 ft3/lb.
100 degrees/16.130 ft3/lb.
150 degrees/16.342 ft3/lb.
200 degrees/16.633 ft3/lb.

The end calculations (volumetric thermal expansion) come out to 1000 gallons @ 50 degrees ends up being 1017.8333 gallons (U.S. gallon), so an 18 gallon expansion tank should suffice, but even if we double it to be safe, we're looking at 36 gallon expansion tanks. But everything I'm seeing says to size expansion tanks to 10% of volume, which makes me think I'm missing something obvious with my smooth brain.

 

[brenndatomu]

That's true...it kicks the burner on at 160* then off at 180*...delta T is ~30-40*