So for the past year I’ve been studying the Garn boilers and found a few things I just can’t wrap my head around or find an answer to.

 

1. What type of metal are they made of?  Carbon or stainless steel?  The reason I’m asking is because I’m interested on how to treat the water in these machines.  I know the company provides a program where you send off water samples, but I’d like to know a little more than that.  What company tests these samples?

  

2. How do you time the length of your burn?  The reason I’m asking is that there are two scenarios, you either set the timer to short and wood is left burning in the firebox which would cause soot buildup, or you set the timer to long and there is no wood left to burn but there is cold air blowing through your machine causing heat loss. 

 

From what I’ve gathered, you kind of have to guess, but which scenario is best?  Would you have to clean the machine a lot more if you timed it to short?  Is there significant heat loss if you timed it to long?

  

3. On these machines, is there a steam/vapor vent going outside to vent any excess moisture?  The reason I ask is because all other boilers I’ve seen have a vent tube going outside.  I haven’t seen one in any of the photos, and since these machines aren’t pressurized air/vapor has to pass in and out of the machine as it heats up and cools down. 

 

Thanks in advance for any help.  Naturally, I’m a really informed buyer and have to know everything about the product before I make a decision.  It can be a curse at times but I guess it’s just the way I’m wired.

sumdumguy:

So for the past year I’ve been studying the Garn boilers and found a few things I just can’t wrap my head around or find an answer to.

 

1. What type of metal are they made of?  Carbon or stainless steel?  The reason I’m asking is because I’m interested on how to treat the water in these machines.  I know the company provides a program where you send off water samples, but I’d like to know a little more than that.  What company tests these samples?

They are made of 1/4" carbon steel.  Precision Chem in MN is the affiliated testing lab.  Martin's recent newsletter outlines some of the key testing parameters.

 

  2. How do you time the length of your burn?  The reason I’m asking is that there are two scenarios, you either set the timer to short and wood is left burning in the firebox which would cause soot buildup, or you set the timer to long and there is no wood left to burn but there is cold air blowing through your machine causing heat loss. 

 

From what I’ve gathered, you kind of have to guess, but which scenario is best?  Would you have to clean the machine a lot more if you timed it to short?  Is there significant heat loss if you timed it to long?

 

 

This is a learning experience.  Generally 1.5-2 hours per load of wood is required to burn down to just coals.  Erring on the short side is better, as puilling cold air through a fire box and heat exchanger with no fire can waste a lot of heat.  Once the fan turns off, the fire will consume the bulk of the available oxygen and go "out" within 15 minutes, limiting the amount of smolder time and therefore soot buildup.  Shutting down in the middle of a full-on burn is not a good idea, however.

 

 

  

3. On these machines, is there a steam/vapor vent going outside to vent any excess moisture?  The reason I ask is because all other boilers I’ve seen have a vent tube going outside.  I haven’t seen one in any of the photos, and since these machines aren’t pressurized air/vapor has to pass in and out of the machine as it heats up and cools down. 

  Thanks in advance for any help.  Naturally, I’m a really informed buyer and have to know everything about the product before I make a decision.  It can be a curse at times but I guess it’s just the way I’m wired.

Look at the pictue of the front of the unit.  There is a vent pipe that sticks out that vents the head space from up in the manway.  There is very little vapor loss from the vent port.

 Hope this helps.

 

 

Thanks for the reply Jim.  I also want to thank you for the right-up you did on the installation of your furnace.  It’s been a wealth of knowledge for me. 

 

If you could bear with me, I have a few more questions for you.

 

Just to clarify.  Is the manway the vent, or is there another vent that comes off the manway that goes outside?  To me, it just seems like you would want to vent any moisture outside.

 

Also, how do the electronics function on these furnaces?  Do you simply set the timer and the exhaust fan runs until the time is up?  If so, wouldn’t it be pretty simple to add an exhaust gas temp. sensor to shut the fan off once it gets below a certain point?  This seems like an easy way to get maximum efficiency. 

 

Is there a sensor that shuts the fan off if the water gets to close to the boiling point?  From what I hear, this is hard to do, but I’m sure it can happen.

 

Thanks for your patience.

 

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The vent tube is just under the manhole cover, it comes out the tube in the front as Jim said.

 

Yes, you simply set the fan timer and let the Garn power vent till the blower stops. Your sensor idea may work well. You do not want the fan to stop with a load of wood or creosote would be a problem and a mess to remove. It is better to have the water boil.

 

Hope this helps, George

From what I’ve read it’s hard to do, but 2000gallons of boiling water doesn’t sound like a good thing to me.  I just figured there would be a safety system in place in case the water got to close to the boiling point.          

 

I also figured they would have a temperature probe in the exhaust tube to shut down the fan when exhaust temps got to low.  This would take the guess work out of it, and would maximize efficiency.  Let’s say you’re doing a burn to get your water up to 200* F and you have the sensor set to shut the fan off when exhaust temps get below 205*F.  At that point your burn would be complete and the best thing to do would be to shut down the machine.  Am I wrong about this?  Do exhaust temps ever get that low with a decent fire still in the firebox?  It sounds good theoretically.

 

Thanks

 

 I hear and appreciate what you are saying in regard to the boilingissue, but I have to say that after working with many Garn owners and doing many installations, it's just not a problem. The simple fact is that getting a Garn to boil takes a monumental oversight on the part of the operator. The thing you have to remember is that you are tdealing with 1500 or 2000 gallons of water. Bringing that volume up even as little as 10 or 15* takes a serious amount of input/burn time. It's not like a "normal" wood boiler where you can overheat in a matter of minutes. For example let's say a person did something a bit on the "duh" side of things and fired his 1500 up when it was already 180*.  Calculating the input required to boil goes like this........ remebering that 1BTU = 1 pound of water, raised 1 degree.  Let's say we have an actual amount of only 1400 gallons in the unit just to be on the conservative side.

So.............

1400 x 8.33 (weight of 1 gallon of water) = 11,662#  Going from 180 to 212 is 32* so 32 X 11,662 = 373,184 BTU's. Simply put, that's a wide open full load burn for a little over an hour in the above mentioned Garn. If you start with a water temp of 160* for example, you have to add over 600,000 BTU's to reach boiling. That amount of heat would be pretty near the most heat gain you could get from a jam packed load of wood. I would guess that you would actually have to reload to get 600,000 BTU's transfered into the water. 

As Jim said regarding the vent, it is right on the front of the Garn where it can be seen and monitored. As it should be. The is very little, if any steam emitted from that opening. In fact about the only time I have seen any thing actually coming out of the vent is when the unit is overfilled or someone does what I just described as being very difficult to do. Believe me, those types are out there and they breed. ;) 

I have found that all my customers usually have a handle on the burn time/load size/temp rise equation within just a few days or a week at most. It really is not that difficult or hard to understand. My 10 year old grand daughter is capable of loading and firing their 2000. 

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Thanks for the comment Steve. Your calculations put the boiling issue in perspective.

 

I just ran the calculations on my 2000 and noticed the differenced in output BTU’s between the 1500 and the 2000. How is this possible with the same size firebox?

 You'll find that a 1500 will pop the temp up a bit more per load because of the lower water capacity. On the other hand a 2000 is just a tad more efficient than a 1500 due to the additional heat exchanger length. 

Thanks for the input Steve.  I knew it was very hard to do, but like you said, there are a lot of idiots out there.  I tend to over engineer things, but I just figured a simple temperature controlled switch would be nice in case the wife or one of the kids tries to help out and ends up getting the thing to hot.     

Just a thought, but large solar systems have this sort of problem. They use a dump zone, a big coil of pex in the ground. We need to put a French Drain around the building and insulate the foundations anyway, so just include a loop of pex.