System Temperatures

Sunday, December 20, 2009

First Impressions.

It is the Sunday before Christmas 2009, and we've had the GARN supplying heat to our house since Thursday. We got 6 inches of snow yesterday, so before I head out to plow the driveway, I thought I would try and jot down some first thoughts and impressions now that we are "online".

The Installation - When we began this adventure, our plan was to install the GARN in our outbuilding. For various reason this changed, and that change significantly affected our budget and install time. We planned originally for 50% of the GARN cost to go toward install costs. That was way under. Of course this all depends on how much of the work you can do yourself, and the complexity of your install. For me, I did not feel comfortable with the plumbing work, and I also had contractors do the construction of the GARN BARN. I did all the other work, which saved a fair amount over the cost had I used outside help.

The GARN BARN was the budget breaker. Had we placed the unit in our outbuilding, our budget would have come in closer to the 50% of the GARN Cost point. The big trade off was we didn't want to loose floor space in our outbuilding.

So, I guess what I'm getting at, it takes a fair amount of budget to install this unit. I feel you can not get by on much less then 50% of the GARN cost for your install budget if you are considering the leap. Now, with all of this said, my local oil is currently $2.239/Gallon, and at that price, I'm break even in less than 5 years of use. We all know it won't stay at that level, so I feel the payoff will occur sooner.

Initial Performance - After the first night pump debacle we have been able to deliver heat to our house, and domestic hot water. The first "USE" night I stopped firing at 184F. Th next morning my thermometer on the GARN was 138F a 46F degree delta. At 138F, we were a little cool in the house. Since, I have been firing until we reach 200F to 205F. We are still around a 50F delta over night(11-12 hours), but at a 150F ending temp we can still deliver a decent amount of heat from our baseboard emitters. So, that 50F delta works out to about 835K BTUs over that 11 hour period, or about 76K btu/hour. Not so bad!

We are currently burning some very dry and punky oak and apple wood. The GARN seems to be consuming that wood rather quickly when we start to burn. When there was no heat load, I could raise the temp 20F/hour, so that meant I was storing 334K BTUs/hour. Now, with the house heat load present during a burn, I am raising the temp roughly 10F/hour or approximately 150K BTUs/hour. The numbers don't quite add up yet, but I think I am loosing BTUs in my rough approximation of the Temp change per hour, and I still have some REAL loss due to uninsulated Front Face of the GARN, and distribution pipes. I'll fix that soon. The picture tells the story. The left side of the GARN BARN is where the GARN is fulyl insulated, and no snow melt on the roof. The Right side, is the boiler room, with uninsulated distribution piping and unnisulated GARN FACE! Check out the Snow Melt HOT SPOT.

The essence seems to be I need to get the H2O temp to 200F before I go to bed. Then we can flywheel well into the next day before we have to fire again. Oh, and by the way the outside temps here the past couple of days have been in the low to mid twenties. About 15F above the worst case design day.

Another performance note. I borrowed a friends Laser Thermometer and used it to measure the temperature differential between the Supply/Return PEX in the GARN BARN, and the Supply/Return PEX in the House 110 feet away. I could not measure ANY difference in temp between the two points. The resolution on the Thermometer is +/- 1F, so I could be off by 2F, but I don't think that is the case. I will know better when I finish my Maxim "One-Wire" Temp sensors. My design simulations determined the flow rate was 2.2 feet per second, so the time from the GARN to the house is roughly a minute. I believe the PEX insulation is definitely doing it's job. Also, I have snow now covering my PEX trench, and I see NO hot spots.

I will need some more operating time to really figure this out, so I'm sure some optimization will follow.

Final Thoughts - Using any alternative energy source to power our lives is a life style choice when we compare to existing technologies suppied mainly by fossil fuels. The GARN as a heat source is no different. It will not "ACT" the same as my oil boiler that maintains a very tight temp range of 180F to 200F. The end result ultimately will be close enough, and more then sufficient for our needs. We will also be comfortable in knowing that we have gained a bit of independence and control over this element in our lives. After the payback period, we will significantly reduce our operating costs as well!

The Garn is not for everyone, but there are numerous highly efficient alternatives available to us today. We chose the GARN because it fit for us. Hopefully, there is a choice for everyone out there that will allow us all to be able to break the hold the "fossil fuel" machine has on our lives. I know this is soapbox, but we have to do something different, and this is my start!

Finally, This is Christmas week, and time to think more about the season then oneself. I hope everyone has a joyous time with family and friends, and pay's thanks to and celebrates our creator. Also, have a safe New Year, and great 2010. I will update things from time to time, as needed. Most likely not until next year!


  1. I really enjoy seeing your install and hearing you initial experience with it. There is nothing like the feeling you get knowing you are free of fossil fuel for your heat and hot water. I hope you update soon with an end of season report on how everything worked out.

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  2. How did it all work out? Did you pipe to the barn? I am going to install a GARN next year thanks for all the info.