Several questions - help needed!

LesliePercy

Here they are:

First, with a wood-fired boiler, is it absolutely necessary to have a buffer tank? My problem is that we don't really have room for one, except possibly a small one, about 40 gallons.

Second, should these 40 gallons be included in the total liquid quantity when sizing the expansion tank?

Third, I know that nowadays people are worried about flue gas condensation in the boiler, so that a bypass and second pump are added (boiler loop). What did people do in the old days -- especially in the days of gravity systems -- when a boiler loop would not have been possible? Did they simply replace the boiler every few years?

Fourth, I notice that in Caleffi's idronics journals, the placement of the expansion tank is very different depending on whether there is a buffer tank or not. For example, look at Figure 6-3 in idronics 7 in comparison with Figure 6-19 in idronics 10. Does having a buffer tank mean resituating the expansion tank?

Fifth and finally, again to save room, I have in mind the possibility of having a vertical supply pipe of about 13 feet going upwards from the wood-fired boiler after passing through a small buffer tank (40 gallons) and placing both the expansion tank and the system pump there, near the top of the system. This would be an unusual arrangement, but is there any reason why it cannot be done?

Please excuse so many questions. Any help will be greatly appreciated.

Jamie Hall

First no, not really -- but it would help, sometimes a lot, in evening out the load on the system. With a wood fired boiler -- which doesn't change firing rate all that fast -- it may be less important.

Second, yes, if there is a buffer tank you need to figure in its volume.

Third, in the old days boilers and pretty much everything else was made of cast or ductile iron, and built like an army tank. They lasted forever. Not so much any more. To get efficiencies up, and save money, they are built of much lighter gauge material, and corrosion from condensation can be a problem.

Fourth, not really. The most important thing about the pump and the expansion tank is that the expansion tank should be connected very close to the inlet side of the pump.

Fifth, yes it can be done -- but you will need to be very careful about the pressure at the inlet side of the pump. Pumps have very specific -- sometimes surprisingly high -- pressure requirements at the inlet, or they will self-destruct remarkably quickly. You may also run into difficulties getting all the air out of the system.

hvacfreak2

1 ) I would think that 40 gallons would be fantastic versus nothing. I have only ever piped one and thankfully it held a lot of water ( 60 gallons if I'm remembering correct ). This unit was an open type
" furnace " , not a rated pressure vessel .

2 ) If the expansion tank and buffer are both on the closed loop the acceptance volume will need to include the volume of the buffer tank. For the open loop side of the one I piped I did not include an expansion tank and it has been online for 10 years or so with no issues.

3 ) I would guess that a natural draft coal fired gravity boiler was either hot or it wasn't. They had draft gates but I'm guessing they didn't turn down much to intentionally operate in a low enough fire to condense for any great deal of time. Heavier castings and higher quality iron helped with longevity as well I'm guessing.

4 ) I don't have the document although I have browsed through it. If this is regarding a closed loop I would say that it would not matter in the least.

5) If this is a closed loop it will not matter. Make up water location should be at that point as well in a closed loop. If this is an open loop you will need to keep an eye on the water level for the sake of the pump seals.

Ironman

Time out!

Let's start at the beginning: Is the wood boiler pressurized or unpressurized?

hvacfreak2

The majority of these are not pressure rated .The document referenced in the original post indicated to me that the OP should know the difference . I'm not sure our replies are in the correct order either for that matter.

Mark Eatherton

To my limited knowledge, the old smoking stoker that could
idle" (and smoke BIG time) are no longer legal (Thanks EPA). Unless the boiler has a significant amount of storage, it MUST have a large amount of water storage because it will only be allowed to burn at a high, smokeless rate. As Bob pointed out, there are not many American solid fuel boilers that are rated for pressurized operation due to A$ME requirements.

Regardless, if you want to have homeowners insurance, you MUST follow the manufactuer's installation guidelines to the T.

RTFM (Read the FREE manual) and follow it.

ME

hot_rod

Unless you are available to stoke and fire the boiler to the ever-changing load, a buffer is pretty much a requirement. If you have multiple small loads, a zoned system, you also need some buffer.

How much buffer capacity depends on how closely the boiler output matches the load, and how often you might see mild days in the winter months.

First timer wood burners often try to jam the fire box full, light it off and walk away. Wood burning is a very interactive hobby You quickly learn to build the fire to the predicted upcoming weather and temperatures

If you follow the online wood heat chat rooms you'll see folks start out with a few hundred gallons of storage and often end up with 500- 1200 to try and smooth out the burn cycles, keep efficiency high, and run a day or two with out fire building.

If you know the load of the system you can calculate buffer tank size and balance it against cost and space.

Valves or pumps can easily correct condensation conditions, a primitive method is to switch off the pump when return drops below 140F, some brands still offer this output on their controls.

Some of the big unpressurized OWF have engineered to pass the EPA tier 1 regs, not sure how without gasification?

Sure the buffer can be remote above the boiler, if the expansion tank is connected there you establish the PONPC at that higher elevation, may only need a 5 psi fill pressure, if it is the highest point in the system.

There is a ton of good info on piping and buffer tanks in this NYSERDA doc that Siggy developed.

Ironman

hot rod said:

Unless you are available to stoke and fire the boiler to the ever-changing load, a buffer is pretty much a requirement. If you have multiple small loads, a zoned system, you also need some buffer.

How much buffer capacity depends on how closely the boiler output matches the load, and how often you might see mild days in the winter months.

First timer wood burners often try to jam the fire box full, light it off and walk away. Wood burning is a very interactive hobby You quickly learn to build the fire to the predicted upcoming weather and temperatures

If you follow the online wood heat chat rooms you'll see folks start out with a few hundred gallons of storage and often end up with 500- 1200 to try and smooth out the burn cycles, keep efficiency high, and run a day or two with out fire building.

If you know the load of the system you can calculate buffer tank size and balance it against cost and space.

Valves or pumps can easily correct condensation conditions, a primitive method is to switch off the pump when return drops below 140F, some brands still offer this output on their controls.

Some of the big unpressurized OWF have engineered to pass the EPA tier 1 regs, not sure how without gasification?

Sure the buffer can be remote above the boiler, if the expansion tank is connected there you establish the PONPC at that higher elevation, may only need a 5 psi fill pressure, if it is the highest point in the system.

There is a ton of good info on piping and buffer tanks in this NYSERDA doc that Siggy developed.

Some of them are listing their ODWBs as coal burners and thereby skirting around EPA regs for wood burning.