Got a wood Boiler.... how to plumb/control it with radiant & DHW & Storage

[TuckerTerra2000]

Hi! Let me start out by saying I AM NOT a plumber/heater. I am an electrician. My best friend is a plumber/heater but he has very little experience with solid fuel boilers. He is helping me with the whole system but is uncomfortable trying to come up with a solution that will do what I am trying to do.

I finally got a (new to me) wood boiler. It is a Buderus g201 in great shape. I know I have read that it is more of a coal boiler for for $300 and the shape it is in I figured it was a good one to start with.
With that being said, I am building a house mostly out of pocket so I do not have a ton of funds available to buy new fancy equipment.

Here is what I am trying to do; I have a 2600 sqft ranch (counting 1st floor only, not the basement). It has radiant in the slab and 1st floor. I currently have an oil boiler running the radiant. I have not got my DHW setup yet but plan to use a Indirect tank so I can use the wood boiler to assist with heating it. That is where the catch is with plumbing and control...

I do not have thermal storage yet but plan to get something (not sure what yet...). With the radiant I can use the storage water down to 100F (plus/minus). For the DHW obviously that wont work.

I DO NOT WANT the oil boiler to heat the thermal storage, and it has to be automatic because I am gone most weekends in the winter and need the oil boiler to automatically kick in when the wood boiler cools.

Most of the diagrams I have found appear to do 2 things:
1) the petroleum boiler heats the storage (or...)
2) the wood boiler hot water is just teed into the oil boiler hot water. I don't this I want that setup because if it needs to heat the water up a few more degrees for DHW it can if it goes through the oil boiler first....?

If my storage is 'say' 110F when the radiant calls for heat I want the system to pull of the tank until it cant any longer. The issue arises when the DHW calls and the storage is still only 110F then it needs to fire up the oil boiler to heat the water up.

I would somehow have to have a control setup to make it all work, but I haven't worked that out yet. I am thinking I will need a relay and aquastat so if just the radiant calls and the storage is above 100F the oil boiler wont fire. But if the storage is below 100F or DHW calls and the storage is below 140F the oil boiler fires. Obviously I need to control a valve going to storage as well that closes when the the wood boiler cools off.

I figured if the storage feeds the cold water supply of the oil boiler with a diverter valve then the oil boiler would only have to heat the water from 110F.

I attached an original diagram that I found on Tarm's website. Then I edited it how I thought I could make this work. Now I am looking for all your input and critiquing!!

Fire away! Tell me if this will work and what is wrong.

 

[TuckerTerra2000]

I should mention that I intentionally placed the DHW tank on the supply before the diverter valve because I figured I can have that diverter valve set to 100F and it wont affect the DHW.
Again, in case the diagram isn't clear the storage hot water is fed to the return to the oil boiler, not the output.

 

[TuckerTerra2000]

Thinking about it that won't work....

I need to tie the cold return into the tanks someplace.

I also need a circulator between the tanks and wood boiler. When the boiler is at temp it kicks on.

 

[brenndatomu]

Just FYI, many of the well versed boiler guys tend to come around more so in the winter...traffic can be pretty light here this time of the year.

 

[hobbyheater]

I do not have thermal storage yet but plan to get something (not sure what yet...). With the radiant I can use the storage water down to 100F (plus/minus). For the DHW obviously that wont work.

I DO NOT WANT the oil boiler to heat the thermal storage, and it has to be automatic because I am gone most weekends in the winter and need the oil boiler to automatically kick in when the wood boiler cools.

There was time when I heated my storage (1045 imperial gallons) with the oil boiler. It amounted to a 60% savings. If your storage is well insulated, its a good thing.

 

[maple1]

What do you have for an oil boiler?

I think even if it is a new cold start boiler, I would consider using an ordinary tank type electric water heater for DHW. Or a heat pump water heater, even better.

 

[TuckerTerra2000]

There was time when I heated my storage (1045 imperial gallons) with the oil boiler. It amounted to a 60% savings. If your storage is well insulated, its a good thing.

I wonder why there would be a savings? Not saying it isn't true I just can't wrap my brain around it the physical advantage.

 

[TuckerTerra2000]

What do you have for an oil boiler?

I think even if it is a new cold start boiler, I would consider using an ordinary tank type electric water heater for DHW. Or a heat pump water heater, even better.

I have a Granby, it is a cold start boiler. I would consider a heat pump water heater. Had always thought there was benefit from being able to heat domestic partially off the wood. I have a 60 gallon tub so I do have to be mindful of that.

 

[brenndatomu]

If the wood boiler is in the basement the HPWH would be using the warm air from the wood heat to make hot water...that's how it works for me...my Kuuma furnace runs all winter and keeps the basement warmer than it would be with oil heat...so now some of the "waste heat" goes to DHW. Saves about $15/mo over the electric heater that was there.

 

[Tonty]

With the water heater, you’ll have to make your decision based on your expected run time with wood versus oil. I have a heat pump water heater, and I turn it off during the winter and heat my DHW solely with my wood boiler. I don’t pay for my wood, but I do pay for my electricity. I know it costs something to cut my wood, but it’s negligible. I can usually get a winters supply in a 1 1/2 days of cutting. One more day to split it and we are good. Or just convince my boys to do the splitting, which is even better. 😂Plus I enjoy cutting wood. 😁But I do love my HPWH for the summer months.

 

[hobbyheater]

I wonder why there would be a savings? Not saying it isn't true I just can't wrap my brain around it the physical advantage.

Well insulated storage , no standby loss. Put an hour meter on the oil boiler it ran 3 hours a day with no load , when connected to storage only ran for 3 hours every third day!

 

[TuckerTerra2000]

If the wood boiler is in the basement the HPWH would be using the warm air from the wood heat to make hot water...that's how it works for me...my Kuuma furnace runs all winter and keeps the basement warmer than it would be with oil heat...so now some of the "waste heat" goes to DHW. Saves about $15/mo over the electric heater that was there.

Yeah I would believe the HPWH would save over straight electric. I have also heard they do well keeping the basement dehumidified.

 

[TuckerTerra2000]

With the water heater, you’ll have to make your decision based on your expected run time with wood versus oil. I have a heat pump water heater, and I turn it off during the winter and heat my DHW solely with my wood boiler. I don’t pay for my wood, but I do pay for my electricity. I know it costs something to cut my wood, but it’s negligible. I can usually get a winters supply in a 1 1/2 days of cutting. One more day to split it and we are good. Or just convince my boys to do the splitting, which is even better. 😂Plus I enjoy cutting wood. 😁But I do love my HPWH for the summer months.

That is similar to me. I live on a 400 acre woodlot with a skidder and skid-steer so it is pretty quick to fill up 4x4x4 wood bins with stacked split wood. Move them up the the house with my trailer. I have a garage door going into my daylight basement so I offload one wood bin at a time and put it in my basement and roll it to the burner with a pallet jack. It doesn't take me long to do my wood...alone.
If I had to pay for wood or it wasn't as convenient it would be a different story. Especially with oil and electricity costing what it does.

How do you have yours setup to be able to run with the HPWh and the wood boiler?

 

[TuckerTerra2000]

Well insulated storage , no standby loss. Put an hour meter on the oil boiler it ran 3 hours a day with no load , when connected to storage only ran for 3 hours every third day!

Yeah I suppose if the storage is very well insulated it would work well

 

[maple1]

I have an ordinary 80 gallon tank water heater. I use a flat plate heat exchanger to heat it with wood when I'm burning. The plate supply side is zoned the same as my heating zones. The dhw side uses a small B&G variable speed Ecocirc that recirculates thru the tank until at setpoint. Controlled by a Johnson A419. The storage capacity of that should get you from burn to burn. With a high set point and a mixer on the outlet, that's a lot of DHW. I will likely replace that heater with a heat pump heater when it ages out. IMO the best of all worlds.

 

[Tonty]

How do you have yours setup to be able to run with the HPWh and the wood boiler?

Mine is very simple, but I have a different style of boiler. My boiler is a Switzer boiler that has integrated storage. It has a fitting on the storage and it came with a DHW coil (not sure of that is quite the right word) that screws into there. I just put a tee and some valves in my supply line to the water heater. In the summer the water heater is feed cold water. In the winter I close that valve and open the one that runs through the boiler so that the water heater is supplied with water that is already heated by the boiler. I turn my water heater off and enjoy unlimited hot water, at least as long as my boiler storage is hot. I do have a mixing valve on that supply because I heat my boiler storage to 200-212, and I don’t want my DHW that hot. One nice thing about the heat pump water heaters, at least mine, is that it’s a WiFi model, so if I happen to be away on a trip and my boiler goes cold, I can turn the water heater on from an app so that the DHW will be hot when we get home. I haven’t yet figured out how to connect my boiler to WiFi so that it will load and fire itself before I get home….🤔

 

[TuckerTerra2000]

I have an ordinary 80 gallon tank water heater. I use a flat plate heat exchanger to heat it with wood when I'm burning. The plate supply side is zoned the same as my heating zones. The dhw side uses a small B&G variable speed Ecocirc that recirculates thru the tank until at setpoint. Controlled by a Johnson A419. The storage capacity of that should get you from burn to burn. With a high set point and a mixer on the outlet, that's a lot of DHW. I will likely replace that heater with a heat pump heater when it ages out. IMO the best of all worlds.

Ohh that makes sense! So I im theory could do the same thing with a heat pump WH then like you said

 

[Unextinguished]

A few mentions that if you pursue them will open up whole wide and deep libraries of rich content at no or low costs

Anything written by John Sigenthaler in either pmmag.com or a hpacmag.com - especially but not only articles that may have titles and topics that include "wood" "biomass" or "renewables". They span at least about 1.5 decades (on the topics of efficient wood, etc.), all worth looking at, although some of the newest ones find system simplicity start getting dialed down to more of an essence and less of a tapestry - while still offering (newest, simplest thinking) really good function along with the simplicity. Both have article limits unless you register, but you can register at no cost. Look also for one of his hydronics books secondhand on ebay - if you get less than the latest edition, it will still be valuable, and, if you wait and snipe, they are not nearly as expensive as if you don't shop carefully. His newest versions do go into deepest depth on renewables/ integration of renewables with overall systems.

Caleffi's "idronics" publications that are freely available online - especially a couple that are specific to either "biomass" "wood" or "buffer, storage, etc." but there's good content, for learning and integrating hydronics, across many that are not even "seemingly focused" just on wood or biomass.

Anything at NYSERDA's openly available materials in which Siegenthaler is a contributor. Their website is not always great at serving things up or helping find things. Just hammer Google with NYSERDA and Siegenthaler and wood and biomass and hydronics, and other laterally-chosen "warm words" once you start getting warmer in what Google serves up.

Bob "Hot Rod" Rohr, who is closely affiliated with Caleffi but very much does not just push their particular products, has all sorts of various articles in various places, and has at least several youtube videos, although I can't recall whether they are via/ associated with Caleffi, or with heatinghelp.com. There's one on buffer tanks in particular which is kind of a masterwork, in both depth of content, and accessibility of information/ mode of conveyance of information.