piping a wood boiler

Betz

to pay for my wood boiler system in 3 years or less. Your wood boiler manufacturer should have a diagram on how to pipe into your existing boiler. If not email me and I can send you several different options. I installed my outdoor unit directly into my old gas boiler, a direct plumbed option, you can also use a plate as explained also.

sebast

piping a wood boiler

Looking for a piping diagram on how to pipe an outside wood boiler(open system) to a gas or oil boiler,mix valves,dump zone,heat exchanger???

S Ebels

Typically

When tying into an existing hydronic system, we simply install a plate heat exchanger, with appropriate isolation and cleanout valves in the return line. The circ on the wood boiler is wired to run 24/7 or if you want to get fancy, wire it into the burner relay on your gas/oil fired boiler and turn it on/off as needed. Constant circ works best.

You must size the hx to work with as little deltaT as possible or you wind up having to run your outdoor unit at 190-200*. Usually not a good thing.

My advice to you would be to keep the money you will spend on the wood boiler, the wood, the installation labor, the inevitable repairs and maintenance, the hassle, the installation materials, etc. etc. etc. and did I mention repairs................. anyhow. Use those funds to invest in tightening up your house and/or a new properly installed high efficiency boiler, oil or gas, with a smart control set-up.

I'll bet my house that unless fuel goes to $3.00/gallon you will be money ahead in 10 years.

sebast

Thanks for the reply, This is not for my own house just general knowledge. I have seen severial different ways and looking for the right way!! to pump and pipe these outside wood boilers. Wood boiler manufactures are recommending 1" piping with this "piping kit from boiler to house". The info on constant circ. is good but again any diagram on the piping inside with a gas or oil boiler and doing it with a buffer tank involved, mixing valve or heat exchanger. Please post any diagrams or web sites, I have not had much luck on the wood boiler sites for piping info. Thanks

hr

You really

don't want to tie an open wood type boiler directly to your exisiting gas or oil boiler. The open type outdoor wood units will allow a lot of O2 into the system and cause serious corrosion issues.

This is one of the reasons to use a heat exchanger between the two systems. Also it is possible the 12PSI that the closed loop boiler typically work under, will over flow the outdoor, open, heater depending on where it is located.

Every brand of outdoor unit I have installed comes with various piping drawings. some can be found on their websites also.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

hr

Primary secondary

is really the only way to pipe two heat sources like this. The wood boiler would be the primary heat. The gas boiler could be fired by a setpoint control straped on the primary loop. So when the loop temperature drops to the temperature you determine the back up boiler kicks on.

You don't want to circulate hot water from the outdoor unit through the gas fired and of course you don't want the gas fired heating the outdoor unit. This is why the hydraulic disconnect that P/S offers is critical when mixing these units.

Plenty of reading available on how to design and size primary loops and pumps. Dan's "Primary Secondary Made Easy" is one of the best to help grasp this concept. Buy it today!

Still, the plate HX will be important to keep the open system away from the pressurized house piping.

A crude drawing with iso and check valves, temperature and pressure gauges omitted

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

sebast

Thanks Hot rod, yes I have all of Dan`s books and fully understand P/S but it is tough finding info. on tieing in these wood boilers and controlling the two heat sources in the most efficient way. Per your drawing do recommend running constant circ. on P1 and P2? when the wood boiler is fired

hr

I'd control

P1 and P2 from the wood boiler aquastat. Most brands use a nice digital Ranco brand with an adjustable differental. I shoot for a 160-180 operating range. You may lose 10° or more before you get into the building, depending on length of underground and insulation R and quality.

Some brands have a dual aquastat that will turn off the wood boiler pumps when the temperature falls below 140°. This helps somewhat with cool, inefficient, creasote forming burns. Simple but fairly effective to help keep the wood burner in it's sweet spot.

Primary and load pumps would kick on at any heat call.

Mike, from tekmars, sent me a nice clear drawing and wiring schematic for a wood burner with buffer set up. This one used differental controls to bring on/off the buffer.

I think they, tekmar, would help any contractor with control ideas. They are real good at that

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

John Barba1

To eliminate headaches it is best to isolate the open system from the primary/secondary.I know corrosion is not a major problem,reasons beging typically you are not adding fresh water to a leak free system, and the manufactures want you to add corrosion inhibitor at the time of installation.I know a hand full of people that have piped their systems fairly crudely and have been running trouble free for ten years.although I would be intrested to know what heat exchanger would be best for this application.

hr

Corrosion inhibitors in open systems

need to be maintained and replenished. Not for the sake of just fresh water being added, but the fact it is open to atmosphere and fresh O2 is always available.

The corrosion inhibitors main ingrediant is an oxygen scavanger. It gets used up.

Many of the outdoor units now use stainless steel for the inner tank to cut down on the rust through issues.

Plain steel tanks will corrode through when operated as open containers. Hense the short warranties on plain steel outdoor furnaces

New comers to outdoor wood furnace use have a tendency to boil them over, a few times, until they get the hang of building the fire to the load. This is when fresh water is added, and again, the corrosion inhibitors need to be boosted.

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

John Barba1

inhibitor

Central boiler offers a 25 year warranty on all of there boilers.As far as the fire is concerned they have a selinoid that controls the draft.You preset the temp and the boiler will maintain that temp.The boilers are built with a baffel to hold in the hot gases, when the house is not calling for heat the fire smolders almost to the point of going out,house calls for heat and the fire is re lit buy the hot gases and infusion of fresh air.Therefore you do not have trouble with boil out.

John Barba1

inhibitor

Central boiler offers a 25 year warranty on all of there boilers.As far as the fire is concerned they have a selinoid that controls the draft.You preset the temp and the boiler will maintain that temp.The boilers are built with a baffel to hold in the hot gases, when the house is not calling for heat the fire smolders almost to the point of going out,house calls for heat and the fire is re lit buy the hot gases and infusion of fresh air.Therefore you do not have trouble with boil out.

sebast

Thanks for all the info. the run away wood boiler was one of my ? and in having an air damper controlled by an aquastat puts the pieces together.

hr

Trust me

even with air dampers and/or air blowers they will runaway under the right conditions. You cannot completly shut down the air or the fire would die at every "off cycle" of the aquastat. A belly full of red hot coals don't just go out with the flick of a switch!

I've found most overshoot the aquastat by 20° or more if loaded. Try and see, but usually setting the aquastat below the actual "desired" off temperature will help. It's a learning curve.

Keep in mind you have a 6, 8" or more diameter flue going out the top. O2 can, and will get to that oxygen starved fire. Ever see the move Backdraft

Also when they wake from a smoldering shut down and get a biug slug of O2, they smoke like bandits until the gases reach the flash point. Not uncommon for neighbors to call the fire dept and report you home on fire until the learn of your "outdoor furnace"

You really don't want a lot of shut down cycles. Better to burn small hot fires matched to the load.

Often folks buy way oversized wood burners, in quest of the largest fire box. This compounds the stop/ start cycling. Their goal is to buy a large firebox model to cut down on the firetending and loading. Not the best choice, usually

Outdoor burners like this have been run through the labs. At IDEAL dry, hard wood burning the approch 45% efficiency. When they smolder under O2 starved conditions, in addition to substancial pollution, they probably drop into the 30% or lower operating efficiencies!

Burn 'em hot if you got 'em. The EPA is hot on the tracks of these "smokers" I suspect their days are numbered

Just some of my experiences from Missouri, home of the wood burners

www.woodheat.org is a good site to get some wood burning actual experiences tips, and stories, both good and bad

hot rod

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"