Wood & Oil Heat Dual System

Christopher Kowalski

I am building a 3,000 sqft colonial near Worcester, Massachusetts. I have access to 30 acres of forest and want to supplement our oil heat with wood.

I am still trying to decide between forced hot water or forced air. I have seen dual boilers that can burn both oil and wood, but I am concerned about their longevity and servicability.

I was thinking about possibly putting in a separate wood and oil boiler and tying them into the same system. Is anyone familiar with this? I would set the thermostat on the oil boiler slightly lower than the wood, so when I am not burning, the oil would come on to supplement the system.

Any help would be appreciated.

Firedragon_4

I would go with the

two separate boilers. Having installed one of the first HS Tarm's in 1976 in these parts I feel the two work better than the one. Proper piping and controls will protect your home and comfort, JMO!

Betz

Go to

www.centralboiler.com and see if this is something that might interest you. Keep the wood, ash and smoke outside of your house while easily tying into your existing boiler.

Ruthe Jubinville

Wood boiler

Go with the new Tarm. With the blower you don't end up cleaning your chimney all the time. I'm leaving for wetstock in a few minutes but I'll be back Sunday if you have any questions. Jerry

hr

Two different units

would be my advice. The piping, controls, and wiring gets a bit complex. If you want everything automatic. If you want the back up to kick on when the wood goes out you need a hydraulic, or piping disconnect. You don't want to circulate water from the fuel fired boiler through the wood fired boiler. Primary secondary works well to handle this.

Then you generally want a buffer tank for the wood boiler for days when you have a lot more fire than heatloss.

It is nice to have a dump zone or maybe use the buffer tank, should the power go out and you have a box full of fire and no pump circulation. Large, properly installed piping between the buffer and boiler would allow a thermosiphon.

Be sure to check with your insurance company, first!. Not all allow indoor wood fired appliances, and I have found more and more they want a UL listing on any wood fired appliance. Inside or out!

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S Ebels

Outdoor wood burners

If I were in your shoes I would be very hesitant to install one of these right now. Due to pending clean air regulations, many of the companies that are making these are likely not going to be around in a year or two. The reason for this is that virtually none of them will be able to meet the new regs. These units were all designed by welding or fabricating companies that obviously know next to nothing about combustion technology. When they "idle" they produce copious amounts of air pollution and carbon monoxide. This is not going to fly very shortly. These manufacturers will be forced to change their design completely or go out of business. Many will not have the funding or expertise available to meet the new testing requirements and regulations. The same thing happened to regular wood stoves in the lates 70's early 80's. Lot's of good old stove companies closed up for the reasons I just gave. The issue becomes whether the company that made your O/D wood burner will still be around to provide parts and warranty services. Too "iffy" for me.

A meeting to introduce these new regs was held a couple months ago with EPA ASTM and other agencies. From what I heard it was nothing short of a collective gasp from attendees when they brought up the requirements on the screen.

The only wood burners I would consider are the gasification type. This would include Tarm for indoor and Dectra (Garn) for indoor/outdoor installation. There are a couple other indoor units that I saw at ISH in Boston but I can't remember the names right now.

Betz

Outdoor

When my unit goes to "idle" barely a trickle of smoke comes out of the chimney. It smokes about as much as a cigarette actually. About the only time this unit really smokes is when the damper first opens and the wood begins to burn. It goes until full combustion in about a minute or so, so I think your concerns about the clean air problems are not exactly as critical as you may think. Anyway, I don't want to step on toes, just a homeowner with an old house with high gas bills that is a lot happier not paying them now.

hr

It' not when they go into idle

it's when they come out of idle that they smoke and burn very inefficiently till the temperatures get up!

My sources tell me two of the major brands of outdoor wood burners were run through independant labs for testing. Results were in the 40-45% efficient range. This was with dry, hard, seasoned wood. I suspect wet, green, and garbage often burned would pull this down considerably. Find a combustion analyzer and decide for your self1

The gasifiaction units such as the Tarm and others have been approved under tight European standards. The 80-85% efficiency number seems believable when you watch a gasification unit burn. Still it NEEDS to be dry seasoned wood to get the best bang for your wood burning bucks.

All the gasification unit I have checked out have 140° stats to both protect the boiler and keep them running hot and in the gasification range. I've yet to see an outdoor unit employ this simple control to keep them hotter and more efficient. Seems like a simple control to interface.

I have sold and installed the brands Steve saw at the ISH show, this is the way woodburning in the States will have to go to meet the latest EPA tier due at the beginning of '05 and '06. Several states have already clamped down on less efficient outdoor wood burners, I suspect others will soon follow.

I'm all for wood burning as an alternative, IF it can be done with the enviroment in mind

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Betz

Not wanting to get into a P***ing contest

but here are some of the tests they run. I'm not going to get the book because I know how this unit performs. I know VERY WELL that a lot of these systems are inefficient and troublesome. I researched them for quite some time. They've been around long enough to establish themselves as a leader and I'm absolutely sure they'll be around for many many years to come.
http://www.centralboiler.com/efficiency.php

hr

No P contest betz

this is a friendly conversation.

The outdoor units are plentiful in my area. The do serve a need. BUT they are what they are. Pretty much a tin drum suspended over a camp fire:)

The truth to the efficiencies is in the temperature of the burn. Gasification units with the ceramic chambers burn in excessive of 2000 degrees! Therin lies the secret to the efficiency. Also a measurment of the flue gas indicates how much energy is going up the flue, and how much stays behind in the water.

The Tarm website does an excellent job of explaining the gasification process.

Over the years wood furnace manufactures have tried all sorts of methods to wring out more BTUs from the burn. Some use a serpentine coil hX to get more surface area. Turn out you can actually pull too much heatfrom the flue gas and really creasote up those coild. One brand sells a drill powered auger to clean out those tubes. I'd much rather see a clean HOT burn then deal with plugged up HX and creasote issues.

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Betz

hahah on the tin

> this is a friendly conversation.

>

> The outdoor

> units are plentiful in my area. The do serve a

> need. BUT they are what they are. Pretty much a

> tin drum suspended over a camp fire:)

>

> The

> truth to the efficiencies is in the temperature

> of the burn. Gasification units with the ceramic

> chambers burn in excessive of 2000 degrees!

> Therin lies the secret to the efficiency. Also a

> measurment of the flue gas indicates how much

> energy is going up the flue, and how much stays

> behind in the water.

>

> The Tarm website does an

> excellent job of explaining the gasification

> process.

>

> Over the years wood furnace

> manufactures have tried all sorts of methods to

> wring out more BTUs from the burn. Some use a

> serpentine coil hX to get more surface area.

> Turn out you can actually pull too much heatfrom

> the flue gas and really creasote up those coild.

> One brand sells a drill powered auger to clean

> out those tubes. I'd much rather see a clean HOT

> burn then deal with plugged up HX and creasote

> issues.

>

> hot rod

>

> _A

> HREF="http://www.heatinghelp.com/getListed.cfm?id=

> 144&Step=30"_To Learn More About This

> Professional, Click Here to Visit Their Ad in

> "Find A Professional"_/A_

Betz

hehe on the

tin drum over a fire. Anyway, I just think you should check out all of your options as a homeowner Christopher.

hr

These links

shine some more light on wood heat. The www.woodheat.org is a good site for both sides of the story.
http://www.woodheat.org/technology/outboiler.htm

I'm not sure I agree with the radiant loop lengths given in this Central article, or that suspended tube is a one size fits all, but.... It was printed in an enginnering mag so it must be correct

http://www.pmengineer.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2732,23741,00.html

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S Ebels

Betz..........

If you have some test data from an honest to goodness testing facility on any or all brands of O/D wood burners, I'd love to see it. As far as I know I have never heard of ASTM or outfits like Warnock-Hersey doing any REAL testing on these units. I hear claims by all the manufacturers; Woodmaster, Heatmor, Heatsource, Central Boiler, Hardy, etc. etc. that their units put out "around 80%". When I ask to see the data however, it never shows up. Some even say that their units will burn green wood. Sure they might burn it but efficiency is about 15% due to most of the heat being used to dry the wood as it burns.

The only way to achieve high efficiency with wood is to burn it hot and burn it all, using a high mass system to store the BTU's. Check out www.garn.com for some info on burning wood efficiently.

I'm not putting anyone or any company down here, just trying to educate and dispell some myths regarding wood burning.

BTW, my brothers' OD wood burner was putting out over 1100 ppm CO at "idle". This was with very little smoke coming out of the stack. CO2 was past the peak measurement of my Testo. They are all the same in this regard.