Wood Boiler Piping

Bob Gagnon plumbing and heating

Hey everyone, does anyone have any experience installing wood boilers? I'm installing a new Autonom, from Canada/Turkey and there is no piping diagram. The Rep recommended a mixing valve to prevent thermal shock, I figured primary/secondary piping would be better. Thoughts? 2nd question, where the heated water from the wood boiler, through the buffer tank, ties into the gas boiler piping, do I need a 3 way valve there, or will 2 pumps serve the same purpose? Thanks in advance. I'll have a better diagram to post when I get a better handle on this, I'm sure I'll have more questions too.

Thanks, Bob Gagnon

hot_rod

Is the gas boiler a cast iron or mod con, it will determine how best to tie the two together.

Here are the options to protect the wood boiler if it is connecting to a buffer or a high mass cast iron radiator system.

Either a variable speed set point circ or a thermostatic mix valve works best. The variable speed pump needs to connect like this to hydraulically disconnect the load from the boiler fig 7-15c.

What size is the wood boiler. The 281 ThermoBloc has a small Wilo Star 16, good for 8- 10 gpm, so an 8- 10 gpm flow maybe a 100- 120K boiler, fig 6-13.

The 280 protection valve is a 14 Cv so good for larger boilers 180- 200K max.., fig 6-7

Tell us more about the system, BTU/hr load, type of radiation, type of gas boiler.

You probably don't need or want the gas boiler to heat the buffer, so tie it in downstream of the buffer tank.

Do you want a control that automatically switches the gas boiler on when the wood boiler dies down? A solar delta T controller is the best way to toggle between the two boilers.

Idronics 10 has piping and control wiring diagram

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ams for various options.

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Tom_133

We have installed a lot of them, mostly Frolings. The pic that Hot rod is showing with the thermostatic loading valve is what we do. We use ASME buffer tanks sets of 300 or 400 gallons, we build a box and spray foam the tanks in. It's amazing how happy the boilers and customers are with this arrangement. The price… thats another thing, those tanks aren't cheap

psb75

The buffer tank(s) have to match the max. mbtuh of the wood boiler. Something that also needs to be mentioned is a "grid-down overheat protection" (or "heat dump zone") that is mandatory on a system with a cord-wood burner. There is probably a schematic for that in Caleffi's "Idronics" series.

hot_rod

One rule of thumb is the buffer has the capacity to take a 1/2 firebox burn.

Although if you are starting with a hot buffer, you may still need a dump zone. A passive dump with a N.O. zone valve is wise in the event of a power outage

There are a few options for passive and active dump loops. Ideally any dump could go to an indirect or somewhere to utilize that energy.

Gasification boilers can ramp their output down quickly. As long as the firebox door is closed and sealed tightly 😯

psb75

Thanks HR. Yes I forgot that most modern cordwood burners are now gasification. But….there are a lot of "off market" non-gas. burners still out there. I have one. A Buderus three-pass, "up" burner and it has a passive N.O. -valved "dump zone" with two, old-fashioned cast iron radiators above it. Modern Austrian-made pellet boilers also seem to be fairly safe in a grid-down scenario due to their regular use of a blower and the relatively small burn-pot with an electric auger-feed.

Bob Gagnon plumbing and heating

Thank everyone, I'm getting a handle on this now, the first picture here is how the old wood boiler was hooked up, the 2nd picture is my proposed piping for the new wood boiler. Feel free to make any corrections or suggestions. Good to see you're still hanging around here Hot Rod.

The gas boiler is cast iron. There are 4 zones of baseboard, 1 zone of Radiant, 1 zone for domestic.

Looks like the dump zone is properly piped with an NO valve installed.

I'm guessing the btu's needed for the home are 60,000'80,000, this older home is a little over 2,500 Sq ft.

Are these the best ports to hookup the buffer tank?

The manufacturer though a 3 way valve might be needed, to prevent the gas boiler from heating the buffer tank, I'm not sure I need that.

The third picture is a thermostatic mixing valve, we have a rebuild kit for that.

Thank in advance, Bob Gagnon

hot_rod

Yeah, I've used those Themovar valves in the past. They seem to be a Euro type NPT :), hard to seal that connection. looks like all 3 have leaked at some point. Get new fiber washers for the unions also.

You don't want the wood boiler and gas boiler in series, fig 6-11,as the gas boiler loses some of it's output to the wood boiler and its flue. An unfired boiler becomes a cooling tower! The gas boiler should go directly to the load header.

I don't see how you are mixing down the radiant zone? A 3 way off the header is fine.

Pipe the two boilers parallel to the load, here are a couple examples. Fig 6-13 shows parallel, with a mod con con, it can be a cast boiler. A cast boiler does not need a circ, the zones circs will flow it adequately and we don't want it flowing into the buffer.

And a chicken scratch drawing, if the boilers are arranged in the room with the buffer in the middle. Layout in the room is not important, just the piping method.

These pages from Idronics 10, system 3, show how to use a delta T control to run the two boilers. A delta T control has two sensor inputs so it can watch two temperatures and decide when the gas boiler goes on or off line. I like the Resol BS plus, a tekmar 150 will work but doesn't have the nice display and VS pump functions that the Resol does. The wiring is with a plate HX for DHW just use that relay to call on the DHW circ.

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Bob Gagnon plumbing and heating

Thanks so much Hot Rod, I really appreciate it. I think I have it down, but rewrote it to match the configuration here. Does this look right? Two more questions, is the one pump on the boiler return for the wood boiler all I need for that boiler? And does the dirt separator have to be on the return near the gas boiler, or could it be built into one of the Spirovents?…

Thanks again, Bob Gagnon

hot_rod

Yes the wood boiler only needs that one circ. It flows through the protection valve and buffer only.

A check valve at the tank

A 1-1/4 or larger zone valve above the gas boiler. It's closed when the buffer is hot enough, wood boiler running, 160F or more?

When the wood boiler is off, and buffer is cold, ZV opens the end switch fires the gas boiler. The check keeps the gas boiler from going through the tank, all gas boiler output gos to the zone circs.

The delta T control sensor 1 near top of buffer

What is the total gpm load? The 1-1/4 Caleffi Z-one ZV is good for 8 gpm.

How low SWT can you supply? If you can go 140 or below you could add a mixing valve controlled by and ODR control. That would allow you to pull the buffer down much lower, perhaps.

But adds another valve and control. 7-4 shows the loads pulled off through a mix valve, typically a radiant system, where the tank could be pulled down to 100F maybe. So the tank runs a very wide delta 100- 180F!

We have a new 683 motorized ball valve that would handle the flow 1- 2" sizes.

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Bob Gagnon plumbing and heating

Thanks Hot Rod, I can't seem to locate that 1 1/4" zone valve you mentioned. Do you have a model number or manufacturer? The customer is on vacation for a month, I'll finish piping it like you said when he gets back, and let you know.

Thanks again, Bob Gagnon

hot_rod

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Here are the part numbers for the motorized ball valves. These are power open, power close, so you need a RIB relay to operate it.

Belimo may have some spring return versions.

Bob Gagnon plumbing and heating

Thanks for your help Hot Rod, I can't find the 1 1/4" zone valve you speced out, but I found an 1 1/4" Caleffi Z57 in stock, the salesman couldn't find any gpm listed, would that work?…

hot_rod

the 1-1/4 z- one valve is a 7.5 cv. So it can flow 8-9 gpm comfortably

A 1-1/4 sweat, 3 port zone valve is a z300737

24v actuator is z151000 with end switch and terminal block wiring

Bob Gagnon plumbing and heating

Hey Hot Rod I piped these 2 boilers this way, the electrician hasn't hooked up the wood boiler yet. But when I run the gas boiler and it calls for domestic hot water I get counterflow heat migration through the buffer tank return line that has the dirt separator on it. Would I be correct in guessing that an 1 1/4" Swetchek on the dirt separator piping return, will solve that problem?

2nd problem, when I run the heat I get heat migration, also counterflow,, through the boiler supply and 2 upper pipes on the buffer tank. Would replacing the circulator with a circulator with a check valve solve that problem?

3rd question, the radiant zone has no piping to prevent cooler temperature return water, would a simple bypass between the supply and return work in the system?

Thanks for all your help,

Bob Gagnon

hot_rod

I don’t see any hydraulic separation between the two boilers?

Is the gas boiler a cast boiler?

How is the radiant getting mixed down!

Dhw is an indirect as one zone?

hot_rod

This should fix it. Without primary/secondary or a hydraulic sep, you need zone valves to stop unwanted flow. Zone valve above gas boiler is opened when it fires, zone valve at buffer is closed when gas is firec. That should stop unwanted flows.

If the wood boiler has a good shutdown function, I don't know you need the dump zone? it depends on how accurately they feed the boiler :) On a mild day, don't load the firebox, for example. There is a learning curve to heating with wood fired boilers, they need some interaction from the homeowner.

how will you control the buffer tank? The delta T control could manage that so gas fires automatically when the buffer goes cold, below whatever the lowest useable temperature is 150 perhaps?

I moved the lines out on this drawing for piping clarity, certainly they could cross behind the equipment.

The thermovar only needs 3 connections, hot from boiler, bypass return to boiler return, and the return.

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hot_rod

This piping option makes it all happen without zones valves, using closely spaced tees to hydraulically isolate circulations

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Bob Gagnon plumbing and heating

Thanks so much for your help, I think I get it now. I'll answer your questions first, then I have a couple more

I didn't install a hydraulic separator, it's pipie pretty much like I posted in the last diagram I put up here.

The gas boiler is cast iron.

Domestic hot water is supplied through a Superstor, as an individual zone.

The previously installed radiant is mixed down with a Sparco thermostats mixing valve. He had the zone set to 270 degrees, presumably to prevent the boiler from condensing. There isn't any sign of condensing at the boiler. I'd like to install a simple bypass between the supply and return on that zone. Would that work OK here? I'll post a picture.

So I'll add a Caleffi Z57 zone valve in the piping between the buffer and supply manifold. The same one I have on the gas boiler, that opens when powered? Should that stop the migration?

Maybe I'm calling the dump zone by the wrong name, the previous wood boiler was piped with a loop to the 3rd floor baseboard loop, and a normally closed zone valve that opens during a power outage to move heat out of the boiler. This dump zone is piped near the tee on the Trermovar valve, is that ok there? Thanks so much for your help…

hot_rod

if you have a good air tight boiler with a trained operator, the buffer tank itself should act as a over-heat mechanism.

The two “control” zone valves should be standard NC The dump zone needs to be NO, normally open, power holds it closed, when power drops it opens for gravity circulation

No harm in adding a over heat loop, more piping and control complexity and potential for heat migration. A zone valve on the supply, and check in the other end if you do

A fixed bypass will work accurately for radiant mix down at the exact condition you set it. If supply or return temperature varies , and it will, the blended temperature will always be changing. A thermostatic mix valve is an inexpensive option if you need that radiant temperature to be accurate