3 zone, 1 Pump, Boiler/Baseboard, Outdoor wood burner

jlemke

After about 11 years of purchasing my in laws house I am still frustrated with the setup of the heating system.

A little history. This might get a little confusing but I will try my best without making it too complicted. I have a 15 year old boiler with 3 Erie zone valves for the 3 floors of my house all ran by one Taco 007-F5 circulator. About 14 years ago my father in law added an outdoor wood burner and had a contractor install a 40 plate in the loop of the boiler. Each floor has its own thermostat that controls the zone valves (none of these control the boiler fire). When the OWB was installed they installed a second first floor thermostat on just the 1st floor to control the firing of the boiler (for times when its cooler and the OWB is not operating yet, spring and fall). So that thermo calls for heat and fires the boiler and then the zone valves control which floors receive it.

The Taco 007 is wired continuously to keep water flow through the plate exchanger but they have a ball valve choked half way so when the zones are all closed the water still has someplace to go, and circulate the plate water.

I hope I still have you all entertained. I am attaching a drawing of how it is piped, I hope that helps somewhat.

Most of the year I don't need the firing of the boiler because the OWB takes care of the heat. My problems are all over. I think that when it is extremely cold out -30 degree F wind chills my house struggles big time. Partially i feel is that most of the hot water is traveling right through the half choked ball valve and back to the boiler and not going through the zones.

A couple options I am looking at.
1: Should I rewire the boiler back to the way it should be so the pump turns on when the zones call and then put in a separate pump to circulate water through the plate?
2: Is there a way to install a zone valve in place of the ball valve and have that one open when all the other 3 are closed to continue with the circulation of the plate?
3: Completely rip out the OWB and just purchase LP for the rest of my life when I already have all the free wood i can handle?

I hope you found some sense out of all this rambling, let me know what you think.

Thanks in advance.

hot_rod

Less than ideal piping that you have there. It would take some re-piping to get it to behave properly. Choking down those valves is just limiting the energy from the OWB to the system.

Some OWB owners like to keep that outdoor loop flowing 24/7 to prevent freeze up at the boiler or in the lines, this drawing shows a small shunt pump to accomplish that.

If you have a way to get some control wiring from the home to the boiler, adding a delta T control will give you a lot more accurate control over the system, with some repiping.

The HydroLink is not required, it's a product we build to simplify multi pump systems.

jlemke

Thanks for the reply. I guess I should have noted that the wood burner loop is not pictured and does have its own pump to keep 24/7 flow to and from the OWB. The pump on the house boiler is wired to run 24/7 just to keep the water flow through the house boiler and the plate exchanger. So in the event that all the zones are closed the pump water travels through the half closed valve.

hot_rod

Just be sure the house Oil boiler is not heating the OWB, if both pumps run 24/7?

Ideally the boilers should be piped parallel so neither heats the other when the are not fired.

No need for wood heat to go up the flue of the oil boiler and vice versa.

jlemke

I have the tstat for the house boiler turned down about 10 degrees lower so it shouldn't fire. The OWB is pretty much the only heat I use during the season and the house boiler is just there for distribution, emergency, late spring and early fall.

Ironman

If you'll install an aquastat or ETC that senses the ODWB water temp like hot rod shows, there will be no need for for a separate thermostat for the ODWB. All the ODWB manufacturers have that stupid diagram and it seems to be the only method they know of - even though it's wrong.

One thermostat, or zone panel, would signal the ETC that there's a call for heat and it would select the house boiler OR the wood boiler if it's hot enough. But both could not run simultaneously.

You'd need to redo some of the piping as the diagrams show.

GroundUp

Simplest, IMO, would be to add a 24/7 circ in place of the throttled ball valve and relocate the system circ to above the tee (the tee drawn above the 007) to only come on with call for heat. Will need a check valve on the load circ to prevent backflow between heat calls. That way the oil boiler always stays hot using the heat from the 40 plate using the new circ, while the relocated circ will pull full flow from the hot supply port of the oil boiler when necessary. Then wire in an aquastat on the incoming OWB supply line to interrupt the oil boiler burner until OWB supply temp drops to say, 140 degrees- at which point the oil boiler would resume normal operation at 180 or whatever, until the OWB comes back up to temp and takes over.

hot_rod

So if the aqua stat starts the oil when OWF drops to 140, what differential would that stat shut off at? Say you set a 20° differential, oil on at 140, off at 160, seems the OWB would need to climb above 160 to come back in, or else the oil just keeps covering the load, running 140- 160-.

If you set a tight differential, say 5°, the oil may never keep up with the load. That seems to be the downside of an aqua stat control reading only one temperature point.

But unless there is a way to get a sensor wire out to the OWB, it may be the only option. We would like to know when the OWB is catching up and able to take the oil off line.

I agree very few OWB dealers or installers think this through, lowest cost, simplest tie in is their goal.

Ironman

hot rod said:

So if the aqua stat starts the oil when OWF drops to 140, what differential would that stat shut off at? Say you set a 20° differential, oil on at 140, off at 160, seems the OWB would need to climb above 160 to come back in, or else the oil just keeps covering the load, running 140- 160-.

If you set a tight differential, say 5°, the oil may never keep up with the load. That seems to be the downside of an aqua stat control reading only one temperature point.

But unless there is a way to get a sensor wire out to the OWB, it may be the only option. We would like to know when the OWB is catching up and able to take the oil off line.

I agree very few OWB dealers or installers think this through, lowest cost, simplest tie in is their goal.

This is the hardest scenario to get the wood boiler to automatically work with the house: a high temp hydronic system. You've got emitters that need 180* SWT at design temp; the ODWB is supplying 165 - 180* to a plate HX which means you're probably loosing another 5 - 10*; and we're trying to make the system changeover automatically. If it were forced air, you simply size the hot water coil to give sufficient output at 140* and set the changeover aquastat there.

I've thought of using a solar controller or other form of dual point control, but I've never run the scenario completely through to see if it's feasible.

I usually just set the aquastat about 160* and let the wood boiler carry it from there.

hot_rod

And at design conditions you need to drive an OWB pretty hard to even get 180, near constant fire stoking and fuel feeding.

Hopefully there is enough emitter to allow 160F operating condition for most of the season. Expecting 180 at the radiator from an OWB with piping and HX loss is sometimes wishful thinking.

The finer details that a salesman often omit or are unaware of.

GroundUp

15-20 degree diff, typically, depends on the setup though. If the OWB has a hard time making 180 and/or needs constant feeding at design, it's far too small. Mine, for example, is rated at 375,000 max output. I believe it's rated for 8 hours at like 240,000 on a full firebox. My combined heat load between the house, garage, and shop is ~106k at design (-20F) and another ~40k for DHW during use. A full firebox will go 24-36 hours at design, depending on wind and sunshine. At the same time, that same load of wood will go 72-96 hours at +30F if I let it. I can crank every stat up and turn on the snowmelt all at the same time and it has no problem climbing the 15 degree diff in only 10-15 minutes. Typically I try to load for 12 hours at a time to keep stack temps down and muster some efficiency, which is 2-4 cu ft of the 15 cu ft firebox. I run lower temp emitters personally, 160-175 temp range in the OWB.

In the case of BB emitters, I would agree that it'll likely be problematic if the system was designed at 180* SWT. Any decent OWB nowadays will easily run and maintain 200* if need be, I've got a few out there doing it with the aid of mixing pumps in order to remedy the mistake of the original installer with undersized underground lines or shortage of emitters.

Short story long, 140-160 on the OWB supply aquastat and 160-180 on the oil boiler aquastat wired in series ( I think, I have an electrician do these for me as I'm electrically challenged) makes for a self supporting system. OWB stays above 140 SWT and the oil stays dead. OWB falls below 140 and the oil resumes, running 160-180 as normal until the OWB comes back above 160- at which point the OWB takes back over. This OWB aquastat is on the actual OWB supply to to the plate, not the oil side. Someone feel free to correct me if my electrical is wrong, but I'm pretty sure that's what my guy says

jlemke

Thanks for all the response. Lots of things to work on. Every year I spend hours in the basement just looking at the system trying to figure out how to "fix" it. I have had several heating guys look at it and of course the options they give me is to put in circ for every floor, multiple repiping, with a $4000 price tag. Even the local company that installed it (now i think it was one of the first ones that they were involved in 12 years ago) doesn't really have any ideas how to fix it. It is time to figure it out and try to install it the right way.

Solid_Fuel_Man

This is why many wood boiler guys employ thermal storage and low temp emitters. Run the wood to charge the thermal "battery" and draw off that to ride out a day or two with low temp emitters.

In my opinion, high temp baseboard really only works with oil. Gas boilers which like low return temps (mod/con) are much better suited with low temp, as is solar, wood with storage, etc.

It's all a lot of money to remove and replace a good working system, when designing from the ground up, well that's a different story.

hot_rod

Solid_Fuel_Man said:

This is why many wood boiler guys employ thermal storage and low temp emitters. Run the wood to charge the thermal "battery" and draw off that to ride out a day or two with low temp emitters.



In my opinion, high temp baseboard really only works with oil. Gas boilers which like low return temps (mod/con) are much better suited with low temp, as is solar, wood with storage, etc.



It's all a lot of money to remove and replace a good working system, when designing from the ground up, well that's a different story.

And at the end of the day, a typical OWF runs about mid 40% efficient, so better than 1/2 of the fuel (wood) you feed it turns into emissions up the chimney. That's IF you are burning good, dry wood efficiently, not smoldering all day because the load is gone.

But the wood is free :0 Kind of.

GroundUp

That "free" wood costs more than buying gas most of the time lol. I gotta know though, where does that 45% efficiency number come from and what's considered typical? Modern gasification stoves are approaching 85% according to Intertek and modern multi-pass conventional stoves aren't too far behind. Your regular old POS Classic with 18th century technology and a glowing hot stack might be the opposite extreme, but I feel like 45% is pretty stingy nowadays for an average

Solid_Fuel_Man

I'm thinking the Classic with UG lines and bubble wrap insulation is the 45%.

Edit: if you are lucky!

hot_rod

GroundUp said:

That "free" wood costs more than buying gas most of the time lol. I gotta know though, where does that 45% efficiency number come from and what's considered typical? Modern gasification stoves are approaching 85% according to Intertek and modern multi-pass conventional stoves aren't too far behind. Your regular old POS Classic with 18th century technology and a glowing hot stack might be the opposite extreme, but I feel like 45% is pretty stingy nowadays for an average

A number of independent labs have tested OWF, with for emissions and efficiencies, which are tied together of course.

I think it was the Forest Resource lab in WI that tested several brands, burning 4" chunks of dried red oak to get their numbers. I was doing some consulting with a wood burner manufacturer up in MN that was trying to build a stainless "Omega" gasification boiler to compete with the Euro imports.

The biggest issue I see with OWF is they get grossly oversized to the load, usually so owners have large fireboxes for overnight burns. But even on design day they shut down and smolder, worse when low load conditions occur.

This leads to really bad emissions and efficiencies. Then the temptation for remote users to jam old tires and railroad ties in them No wonder they got so much EPA scrunity.

Solid_Fuel_Man

I bet I know which manufacturer you were working with in MN! Built in storage and ID fans anyone?

GroundUp

I'm well aware of this Omega thing, and the MFG that went with it- as their factory is a mere 3 hour drive from my house. They are now out of business due to EPA standards. With that said, their "other" line of OWB were in the running for THE MOST inefficient OWB ever to hit the market. 8" stack and a flat-on-flat loading door with no gasketing was never an efficient design by any stretch of the imagination. If they were anywhere near 45%, the modern conventionals are 97% and gassers 110%.

Intertek has their numbers skewed on occasion also, with that 4x4 test you spoke of, I believe it was the CB E-Classic units a few years back were coming up with 104% efficiency on the chart. Does anyone actually know the real numbers? Doubtful. But weighing the wood and comparing MC%, species, with stack temps and cycle times, CFM intake, and the whole 9 yards we're able to gather a somewhat educated number. 45% for an old pressurized tube-in-tube like the Therm was, is laughable at best IMO.

As for oversizing though, absolutely. Vast majority is just that, for the reasons mentioned. SO many look at the stove size as the storage volume being equivalent to output. MFGs like Central make their stoves hold a huge amount of water for storage to make up for the crappy design otherwise so that it can build and store enough heat between heat calls to make it work. A properly designed stove like MFGs like Heatmaster and Crown Royal have got now are able to produce on demand and shut down between, without much need for storage which helps tremendously with efficiency

hot_rod

Good intentions on the part of the team at Aquatherm with the Omega projects. They tried to mimic the Euro designs which are the most efficient solid fueled boilers around, I feel. Welding that complex shaped in stainless may have been the downfall.

The Euros relentless engineering and emission standards drive them to manufacture the high efficiencies.


I feel the Austrians are known for some of the best pellet designs. They have an entire hall at the ISH show showing all the manufacturers and their products.

Troy Boiler works in NY builds a really nice gasification units, pellets or chips. Their EcoWorld product is a Euro design. Check them out if you haven't already. The Econoburn is another nice US built cordwood gasifier.

I'm not a fan of large water content type units if it's outside. I'd rather store energy inside the heated space so you don't have a 180∆°t working against you You could probably heat a small village in Europe with gasification boilers with the same amount of wood some OWF burn in a season.

I've seen Hardy installs in Arkansas with 1" un-insulate pex just lying on top of the ground, because you know "the wood is free"

Solid_Fuel_Man

Wood=work. Free or not, I get it both ways, and it still=work. Personally, my time is worth something, so less work means less time, in all aspects of woor burning.

Efficient design, both on the fire side as well as the water side (storage, smart piping strategy) and on the electrical side with staged heat load and fully automatic control, for that time when you forget to open some valve or flip some switch.

Far too many installs are just the opposite. It turns into a hobby of sorts, a money saving healthy one hopefully!

GroundUp

I've got 40 acres of red oak on my hunting land that was dying faster (oak wilt) than my dad and I could cut and burn it. He's nearing retirement age and I had a bulged disc 4 years ago that won't allow me to cut more than 1 tree or swing a maul anymore without crying, so the both of us just started buying 8ft lengths from a local logger and having him run it all through the firewood processor. A semi load will heat both our properties all winter, at a cost of roughly $1800 without lifting a finger for processing. Every fall I'll load up the Bobcat and grapple and haul it to the woodpile, and him and I will spend a weekend hauling it all home and stacking. He takes roughly 6 cord to heat 4500 sq ft and I take 7 or 8 to heat 6800 sq ft and snowmelt in my sidewalk. We both heat DHW also. So the $1000 I spend annually to heat 3 buildings and a sidewalk on top of DHW for 3 definitely wouldn't go far if I were to try to accomplish the same feat with LP. The equipment is all stuff I'd own anyway even if I didn't burn wood, so realistically it's the cost of wood and a weekend worth of time- maybe $30 worth of fuel. No it's not free but it's the lesser of 3 evils IMO. Of course the daily feeding of the dragon is a bit of a PITA in comparison, but it's just part of the daily chores. 2 minutes twice a day isn't so serious in the grand scheme of things. For example, I heated the house with LP and outbuildings with the electric boiler a couple years ago for exactly 1 month and that one month cost just over $800 itself.

My stove does hold 180 gallons which I feel is less silly than most of similar output that hold 400, but less would be ideal. Mine is an outdoor unit but it's located inside a heated building, so what little heat is lost due to the internal storage is lost into the shed. It shuts down tight enough to lose almost nothing out the stack during idle, roughly 1500 BTU/H total loss through the stack and jacket combined according to my documentation last year and I would be willing to bet the stack contributes almost none of it. At idle, stack temps stay room temperature.