# want feedback piping WOOD boiler gas mod/con backup via reverse indirect BUFFER tank



## rainmaker (Dec 2, 2013)

For those of you with hydronic plumbing experience, I am looking for feedback on how to connect my wood boiler through buffer tanks in parallel to a gas LPG backup boiler to heat radiant floor and DHW hot water indirectly.  I intend to fire the wood a majority of the time and expect the gas backup to only run during times we fail to feed the flame or during mild seasons for hot water, etc.  

Look at my preliminary schematic plan below... Is this piping simple enough to install and maintain myself yet flexible enough to buffer both and alternate heating source automatically?

I'm aiming for a common low-loss header (or similar closely spaced Ts as in primary/secondary piping) that can route the hot water from either boiler, as needed, based on smart control wiring.
My original question at the Heating Help forum:<http://www.heatinghelp.com/forum-th...ckup-via-reverse-indirect-BUFFER-tank/success>

Bear with me as this is my first time posting ... I will reply back to add more info on my house and system if it helps bring more constructive comments.  (hope that works...)
Thank you in advance.


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## rainmaker (Dec 2, 2013)

links to images of my crude sketches of a few ideas.
i give a lot of credit to the Caleffi idronics 10 spiced up with some Siggy advice (the great Siegenthaler) and a lot of other good comments by others too...

HOW DO THESE LOOK?

I'll describe the indoor wood boiler set up next...
note: the wood boiler buffer is a challenge since there is only a narrow doorway to get down the hatch into the existing stone basement, so either multiple pressure tanks ganged with reverse return or a big fat unpressurized DIY water tub...

Question: if pressurized storage, could the last buffer be a reverse indirect for DHW and mediate between gas mod/con and micro-zone in shoulder season bypassing the other wood storage but still be included in the wood capacity while burning?

Am I asking too much?




LINK-nonpressurized




LINK-pressurized optA




LINK pressurized optB


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## rainmaker (Dec 2, 2013)

*bout that WOOD boiler:*
regarding the previous posts... we found a refurbished indoor WOOD BOILER.
the smallest i could find (heat output capacity) was Itasca 85kBtu with 20 gallon water jacket. it has big threaded S&R ports with a thermostatic air intake damper.





my understanding is that since this is almost double the output needed for heat load, then BUFFER tank is needed, so I'm shopping for used propane tanks to gang together as pressurized (and fit thru the narrow hatch to the cellar) or building my own EPDM lined tub as unpressurized storage and choose between external HX or submerge some copper coils...

So ? How do I pipe the wood as primary source with storage to a low loss header and add gas mod/con backup that also needs a little buffer and all play nice?

Could a reverse indirect DHW tank serve multiple purposes and transfer heat at the cross roads?

Thanks again everybody!


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## rainmaker (Dec 2, 2013)

House is approximately 1400 SF, 2-story, detached, built 1850s, stone footing log floor balloon stud wood frame in upstate NY near Kingston in the historic Hudson Valley.
Basement full height under 700 SF ground floor under 700 SF 2nd floor under Attic with new spray foam insulation at roof line.
Heat loss measured before foam was huge, as any old drafty house.
Next blower door test due after more air seal work...
HEAT LOSS between 40-50 kBtu, but I'm convinced I can get it down even lower!
Radiant design PEX stapled up to thick aluminum Joist-Trak @ 8"OC with batt insulation below each level (plus reflect barrier above basement). 
Distribution may only consume around 37kBtu estimated all in... which is why I may need to add future supplemental zone of higher temp radiators to make up difference, but I prefer not.

Indoor WOOD boiler as primary, but more on that next since I want to install LPG gas mod/con backup first and tie in wood later... (my existing oil furnace is temporary heat and taking up the space of future wood unit).

Backup source GAS mod/con was proposed Triangle Tube Prestige 110 but I did my homework and prefer to size as small as possible (finding many threads warning against over-sizing). Intend to go with Prestige 60 that just covers our extreme maximum worst-case and turn down ratio modulates to about 15kBtu.

Zones calculated via Uponor app are 1-main floor 21kBtu, 2-upstairs bedrooms 15kBtu, #3-bathroom 3kBtu. MICRO-ZONE! time for a buffer tank for the gas unit to avoid short cycling.

My original preference was pipe Primary/Secondary like the good manual says, and after debating zoning via pumps vs valves, am leaning toward ECM circulator variable speed delta-P like Grundfos ALPHA and 3 zone valves. Manifolds EP with integral flow balancing etc. 

DHW was going to be a SMART tank indirect. we have an old electric water heater 40-gallon that seems to keep up, and I'm heeding advice to NOT increase boiler size for domestic hot water, so idea was to increase to 50-gallon... until I warmed up to the idea of reverse indirect to also serve as buffer tank and also as hydraulic separation instead of closely spaced Ts on P/S loops. 

Now considering something like the ERGOMAX or Turbomax or even retrofitting the old electric DHW tank as dumb buffer... Is this reverse indirect a good idea?  How can my piping be improved to do what I described?


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## maple1 (Dec 2, 2013)

Here's what I came up with for mine. I did some tweaks since I drew that up, while putting it together, but forget what now. Substitute electric boiler with gas.

Wood sends to storage (and system when calling for it), when that goes cold the call changes to the backup via aquatsat on supply header. Each has its own circ & with the check valves the backup won't send heat to storage. There's likely fault to be found with it - but it's way simple, and it works. (You've got me lost in a lot of what you talked about).


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## Nofossil (Dec 2, 2013)

Can you get a tank with the HX in the top for your reverse indirect? The coil is normally in the bottom, which won't work in your case.


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## PassionForFire&Water (Dec 2, 2013)

rainmaker said:


> like the ERGOMAX or Turbomax or even retrofitting the


 
Looks like the Ergomax and Turbomax are the same
http://www.ergomax.com/Specs.htm

As long as the DHW coil is copper or SS you are OK.

There are tanks out there were the coil is carbon steel and glass lined on the outside
You can not use these for this purpose.


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## ewdudley (Dec 2, 2013)

Danger, Will Robinson!


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## rainmaker (Dec 2, 2013)

Thanks, Maple1.  Looking at your diagram might help me simplify my proposed system.  I'm sure it will bring up a bunch of questions... and right away I wonder why normally open from your wood boiler to the zones?  I would think to err on the side of caution to have it normally closed so it feeds storage unless the system is energized properly to handle the amount of heat... I would not want to sizzle my pex floors... but i guess a 3-way tempering valve before the distribution as I show would control that too.   
I do like that you can bypass storage to start heating immediately and slowly build up reserve... 



maple1 said:


> Here's what I came up with for mine. I did some tweaks since I drew that up, while putting it together, but forget what now. Substitute electric boiler with gas.
> 
> Wood sends to storage (and system when calling for it), when that goes cold the call changes to the backup via aquatsat on supply header. Each has its own circ & with the check valves the backup won't send heat to storage. There's likely fault to be found with it - but it's way simple, and it works. (You've got me lost in a lot of what you talked about).


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## rainmaker (Dec 2, 2013)

Ha, ha!  that looks like a pressure vessel modified with extra fittings?  
please explain...



ewdudley said:


> Danger, Will Robinson!
> 
> View attachment 119282


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## maple1 (Dec 2, 2013)

*I wonder why normally open from your wood boiler to the zones?*

That's my dump circuit, for power outages when I happen to have a fire burning.


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## ewdudley (Dec 2, 2013)

rainmaker said:


> Ha, ha!  that looks like a pressure vessel modified with extra fittings?
> please explain...


That's a home-brew reverse indirect buffer tank as shown in both Option A and Option B.  It's just a 30 gallon propane tank with ports and temperature wells added according to the requirements of my situation, as well as the 'tankless coil' ports for the two HX coils.  (It's less than 120 gallon, which exempts it from certain regulatory requirements here in NY.)

My setup uses Option B where there is a separate transfer pump for feeding the buffer tank from storage with these differences:

Additional HX coil for hot tub.
System load draws from a point below the HX coils, so DHW always gets priority.
Aquastat well for DHW located near bottom of DHW zone.
Aquastat well for system load located a few inches up from return ports.
I call it my nexus tank.  I can feed heat in from wool boiler storage tanks, oil boiler, or coal boiler.   System loads, DHW coil, and hot tub coil pull heat out.  Additionally radiant floor loads pull from bottom of buffer and return to bottom of wood boiler storage.

I definitely recommend Option B where the flow of heated water from wood boiler storage to buffer tank can be controlled.  That way it is easy to minimize return temperature to storage and thereby maintain maximum storage stratification and heat storage cycle capacity.


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## rainmaker (Dec 3, 2013)

Thanks for the comments so far... Here is a new version (see link)
Please comment if there is a better way to pipe the bypass to and from storage?





http://i1165.photobucket.com/albums...177LWR-12_03-pressurized_optB_zps58aba9ea.jpg

My goal is to sequence like this:
1. Wood fires and recirculates bypass until up to temp.
2. wood circ to storage (normally open in case of power failure).
3. DHW or SH heat call opens 3-way valve wood circ to buffer tank "header" until satisfied then disconnects and resumes to storage.
4. If DHW or SH call but wood too cool then activate valve and storage circ to buffer.
5. If both wood and storage too cool, then gas backup boiler fires.

Due to hydraulic separation at central buffer tank, the heating zones can pump at their own rate as needed, as long as the tank is hot. The tank would recharge itself as needed also.
(I still have to figure out control specifics, including ODR outdoor reset...)

Is there a better way? perhaps thermostatic 3-way instead of off/on diverting...?
Thanks.


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## ewdudley (Dec 3, 2013)

rainmaker said:


> Please comment if there is a better way to pipe the bypass to and from storage?


I think your "177LWR hydronic 11-28 pressurized optB" above is correct, simpler, and better.  Wood boiler heats top of storage, transfer pump draws from top of storage to satisfy buffer.  Most all wood boiler storage systems separate the function of charging storage from the function of drawing from storage, for good reason.


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## rainmaker (Dec 3, 2013)

I hear you, however the Heating Help guys are really emphasizing the point that it would take a *looooooong* time to heat up many gallons of water in storage before even available to heat the house or domestic...
Prioritizing DHW or SH heating would be most convenient for our family, I believe, as long as it is not problematic.

Because I am limited on space for storage, I may have to use as much heat concurrently as I can and simply feed it more frequently. It will surely be less frequent than the old wood stoves we are accustomed to... (i hope).

That latest version does feed to top of storage and also draws from top also to preserve stratification.



ewdudley said:


> I think your "177LWR hydronic 11-28 pressurized optB" above is correct, simpler, and better.  Wood boiler heats top of storage, transfer pump draws from top of storage to satisfy buffer.  Most all wood boiler storage systems separate the function of charging storage from the function of drawing from storage, for good reason.


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## ewdudley (Dec 3, 2013)

rainmaker said:


> I hear you, however the Heating Help guys are really emphasizing the point that it would take a *looooooong* time to heat up many gallons of water in storage before even available to heat the house or domestic...
> Prioritizing DHW or SH heating would be most convenient for our family, I believe, as long as it is not problematic.
> 
> Because I am limited on space for storage, I may have to use as much heat concurrently as I can and simply feed it more frequently. It will surely be less frequent than the old wood stoves we are accustomed to... (i hope).
> ...


Sometimes heating help ain't.   Those guys show remarkable sophistication on many topics, but wood boilers with pressurized storage isn't one of them.

With pressurized storage, you're not waiting to heat all of storage, you're just waiting to heat the top of storage, which is only a couple gallons even if you're using a 1000 gallon tank horizontal with inlet from boiler on one end and outlet to load on the other.


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## rainmaker (Dec 3, 2013)

The wood firebox on the Itasca is decent but not huge.  I did a trial run and stuffed about 50 lbs of split oak packed pretty tight.
It was a big full armload and I weighed it.  
6,200 Btu/lb wood x 50 lb wood per load = ~ 300,000 Btu
*80% efficient (old model) = 250kBtu / 90-F Delta_T (to raise from about 90F to 180F during recovery) = 2700 lbs water /8.33 factor 
= 325 gallons storage.
Boiler 20 gal + 26 gal buffer = 46gal, net 280gal = (3) @ 100-gallon tanks or even (1) @ 250 gal vessel.
Does that math seem realistic?One big 250-gal propane pressure tank or a few smaller ones is about all I can fit reasonably in the basement.  

So if I can improve my heat loss down to 30kbtu to match the radiant heat distribution capability, then that 300k storage should last between 8 - 10 hours... (on coldest days of season) right?  
If that works then I would anticipate loading the firebox once in the morning and once at night... maybe only once a day during milder months.


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## ewdudley (Dec 3, 2013)

rainmaker said:


> So if I can improve my heat loss down to 30kbtu to match the radiant heat distribution capability, then that 300k storage should last between 8 - 10 hours... (on coldest days of season) right? If that works then I would anticipate loading the firebox once in the morning and once at night... maybe only once a day during milder months.


That's the thing I like about hydronics, if your estimates going in are realistic, or better yet provable, then everything _will_ work as planned according to some pretty simple calculations.

You should be able to finesse more time between burns by slowing the boiler burn rate down somewhat and timing the burn so that storage maxes out more or less when the fuel runs out a couple hours after you're gone.  Also running storage up to 190 degF is doable if need be.

And by all means maintain focus on minimizing heat loss.  The best kind of heat is the heat you never needed.


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## maple1 (Dec 4, 2013)

I'd just put as much storage as possible into as much space as I could make for it. I don't think there is a downside. I put in 660 and am still trying to figure out how I can cram more in. The more you have, the more flexibility you have, the longer you can go between burns, the better it will fit your schedule. I know now there are lots of days the past month or so where if I had say another 330 or so it would have allowed me to skip a days burning - which standing back & assessing things could end up adding up to something significant by the time heating season is over.


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## rainmaker (Dec 4, 2013)

Yes, good points.  However, I am looking at it from the perspective of how much can that particular stove burn in one full load... and the most storage needed without blowing the pressure relief.   I'm aiming to burn as wide open hot as possible to avoid creosote or flue gas condensation (in the wood boiler).   
So theoretically if I packed it full, let the storage and the buffer absorb the entire BTU energy boost... then I have about 10 hours of peak heat loss (or even longer time between burns during mild weather) which sounds like a lot of flexibility to me, without having to add extra storage.

My point being, we plan to have a backup gas boiler and not afraid to use it.  ...and that little firebox can only fit so much.
When would I ever realistically "need" more storage?  

I'm near Kingston NY with about 4,500 - 7,000 Heating Degree Days average per year.


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## rainmaker (Dec 9, 2013)

So the idea of reverse indirect is being questioned by my plumbing sales guy.  They claim the smaller backup boiler (60k mod con) might not be enough to power something like the Ergomax or the domestic hot water might suffer.
Supposedly Turbomax can add extra system ports... waiting for reply.

I wonder if the reverse indirect idea is not good for a system of this size?There are other ways to buffer the micro zone...


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## rainmaker (Dec 9, 2013)

... the more i consider, perhaps the Tarm bioheat PT2 concept might be a good one for this application?

Plumbing Schematics Document

http://www.woodboilers.com/images/stories/documents/woodboilerplumbingschematic1211.pdf


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## ewdudley (Dec 10, 2013)

rainmaker said:


> So the idea of reverse indirect is being questioned by my plumbing sales guy.  They claim the smaller backup boiler (60k mod con) might not be enough to power something like the Ergomax or the domestic hot water might suffer.
> Supposedly Turbomax can add extra system ports... waiting for reply.
> 
> I wonder if the reverse indirect idea is not good for a system of this size?There are other ways to buffer the micro zone...


I cannot understand what they're trying to get at by saying the mod con wouldn't have enough power for the Ergomax.  When you're all said and done it's a tank with a couple dozen gallons of hot water and a HX in it. The power required is dependent on the heat load drawn from the tank and has nothing to do with the tank itself.

The aquastat well is high enough in the Ergomax such that DHW can be prioritized by disabling system loads while Ergomax is in a recovery cycle.  Or perhaps adding a surface mount temperature sensor a few inches higher would be a better indicator of when the heat source was falling behind temporarily.

With a mix of differing temperature loads and the bulk of your system loads being low temperature radiant, a reverse indirect buffer/separator is ideal for your situation.  Ideally your low temperature radiant loads would draw from the bottom of the reverse indirect tank.  Opt B above should be your preferred design type.


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## rainmaker (Dec 10, 2013)

About the reverse indirect DHW capacity, they mean that with a smaller volume of domestic water in the coil it might deplete faster without a much higher temperature system water.  A faster recovery with a bigger boiler might compensate but supposedly this 60k is on the small side?   I am not sure and I hear what you are saying.  I do want to look at the numbers again...

However, they did offer a solution to buffer the micro zone by piping off the DHW branch (an example in the Triangle Tube manual).
Then pipe the rest primary/secondary typical.

example from Prestige manual:






ewdudley said:


> I cannot understand what they're trying to get at by saying the mod con wouldn't have enough power for the Ergomax.  When you're all said and done it's a tank with a couple dozen gallons of hot water and a HX in it. The power required is dependent on the heat load drawn from the tank and has nothing to do with the tank itself.
> 
> The aquastat well is high enough in the Ergomax such that DHW can be prioritized by disabling system loads while Ergomax is in a recovery cycle.  Or perhaps adding a surface mount temperature sensor a few inches higher would be a better indicator of when the heat source was falling behind temporarily.
> 
> With a mix of differing temperature loads and the bulk of your system loads being low temperature radiant, a reverse indirect buffer/separator is ideal for your situation.  Ideally your low temperature radiant loads would draw from the bottom of the reverse indirect tank.  Opt B above should be your preferred design type.


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## rainmaker (Dec 10, 2013)

Hey, can anybody help explain the sequence of operation on the wood boiler side of this typical piping diagram by Tarm aka Bioheat?
(See below)

Does it flow from both storage tanks and boiler simultaneously?When the fire cools, how does it draw from storage and not boiler?
What does the zone valve do?
I found another thread that explained what the 3-way diverter valve does, but it would help to get another explanation...

thanks!



rainmaker said:


> ... the more i consider, perhaps the Tarm bioheat PT2 concept might be a good one for this application?
> 
> Plumbing Schematics Document
> 
> http://www.woodboilers.com/images/stories/documents/woodboilerplumbingschematic1211.pdf


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## ewdudley (Dec 10, 2013)

rainmaker said:


> About the reverse indirect DHW capacity, they mean that with a smaller volume of domestic water in the coil it might deplete faster without a much higher temperature system water. A faster recovery with a bigger boiler might compensate but supposedly this 60k is on the small side?


With a reverse indirect, reserve DHW capacity is in the buffer tank, not the coil.  With an Ergomax E23/E24 you have up to a 26 gallon head start, with the E44/E45 it's 48 gallons.

If the Ergomax size is insufficient you can plumb the backup boiler to heat some portion of your main storage instead of going directly to the reverse indirect, and let the backup boiler get ahead of potential DHW shortages that way.

Also if the Ergomax seems costly, you can look at installing a 'tankless coil' in the top of main storage and doing away with a separate water heater.


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## rainmaker (Dec 12, 2013)

Ergomax smaller tank is limited to about 3 or 3.5 GPM max flow.  That's enough for maybe a shower head and a faucet.  But our bath tub spout which is nothing extravagant flows 5 GPM.    Even with nothing else running hot water, I just don't see that working very well.  Even with the next size up boiler at 100KBtu and the next size up Ergo... still not quite there.  After reading dozens of forum threads on the subject, I see about half saying it works for them (without specific use details) but also half warning specifically that it won't be enough.  We have the BTU but the bottle neck seems the size of the HX coils... (edit)  ... combination of small boiler with small HX coil... according to their chart if we had 150kBtu it might flow enough but probably at 180*F ... but the whole reason for buffering in the first place was the boiler already being too big!

ewdudley: I would be curious to know how your situation works and compares to the Ergo in spec?
I want to make this work, i do...

Now if the Thermo2000 people would actually call back, I would consider a Turbomax with extra ports.  The product rep emailed and says they do but then won't reply back or return phone calls... (maybe by luck it is vacation week?) and the other sales rep Rathe way down in NY did not know and deferred to another rep who has not called back... maybe i just don't know the "secret knock "...

No worries. I can fab my own buffer or get a BB-30 boiler buddy and just pipe the regular indirect DHW tank, or P/S and buffer the micro zone off the indirect like the book shows... just messy and more parts and labor.



ewdudley said:


> With a reverse indirect, reserve DHW capacity is in the buffer tank, not the coil.  With an Ergomax E23/E24 you have up to a 26 gallon head start, with the E44/E45 it's 48 gallons.


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## rainmaker (Dec 12, 2013)

Here is my latest version with a lot of credit to Caleffi idronics_10.
I have not given up completely on the buffer tank/ hydro-separator/ low-loss header, but decided to sketch an alternate layout that is more "conventional" using primary/ secondary closely spaced Tees for comparison.  Link to piping diagram:



My previous posts in this thread with some good feedback about wood boiler storage helps me feel confident that bypass might actually be redundant, so I'll plan on pulling hot water right off the top of the storage as soon as it is available... hoping it won't have to heat up the whole thing before it is useful.

I hope this piping allows either boiler to run independently, and each zone run independently also.
DHW indirect domestic hot water is pumped as a zone also (after the Tees) so it can pull from either boiler source without interrupting that primary flow...
The micro zone is pulled off the indirect tank on another loop to help buffer.  Thanks to Triangle Tube piping examples in "Prestige Application Booklet".

Anybody have any ideas to improve upon this layout?How would I control this thing? (I can post the idronics wiring schematic next...)
3 thermostats total (2 zone valves shown and 1 micro zone)

thanks again.


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## ewdudley (Dec 12, 2013)

rainmaker said:


> I would be curious to know how your situation works and compares to the Ergo in spec? I want to make this work, i do...


The 'tankless coil' DHW HX in the reverse indirect I built (photo above) is rated nominally at 5 gpm, whatever that means.  I set it up with stainless steel circulator to keep a conventional 50 gallon electric DHW charged.  It turned out that with 140 degF in the indirect tank the unit can supply hot water for two low-flow showers and the clothes washer, not much demand really, but it's all we need.  So the electric water heater is now valved-off, I run the pump from time to time and heat the tank once a year or so just because.  The performance specs on this stuff very hard to come by, so all I can offer is a hunch that a 5 gpm finned tankless coil probably has more capacity than the coil in the Ergomax E23, their smallest unit.

It looks like your storage will be fairly close to to your DHW loads.  You may want to look at putting a 'tankless coil' in the top of one of your storage tanks.  The fittings are reasonably priced and the welding shouldn't cost a lot either.  The coil itself is a couple hundred dollars.

Threaded style like so:





Or neck and flange type like I used could be installed in the top of a storage tank:




I thought you had some high temperature loads, but it looks like you're feeding all lower temperature radiant loads.  As I see it the big advantage of a buffer/hydraulic separator tank is that it makes it easy to do a good job of minimizing return temperature to storage.  With low temperature loads fed by mixing valves the problem of minimizing return temperature to storage pretty much goes away.  Therefore I believe your heating loads could all pull directly from storage, and then you don't need the buffer/hydraulic separator at all.  Storage becomes your reverse indirect and your hydraulic separator.

And your backup boiler can also connect to storage directly, same as the wood boiler.  You would only heat up enough of storage to supply heat to the DHW coil.  I can testify to the fact that the hot water stays a the top of the tank quite well.


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