Boilerman,
How much coil can you fit in a pressurized tank using a 1.5 inch hole. How much length? How much surface area?
I just worry about getting enough heat from the heat exchanger in the tank. I know with the open system, you can easily put in lots of coil that encompasses most of the tank to get as much heat out of the water as possible.
Leaddog,
I considered that option as well. I know the tank we have has very little piping in it. It is a 40 gallon tank. Not exactly sure of the coil length, I know it is steel. I have heard that they are about 5 to 15 sq feet of surface area generally. 120 feet is more in the 30 to 35 foot range and am told should be plenty to pull heat out of the tank. I just worry about the complexities of adding another tank on top of the two 500 gallon tanks we would add. How many feet of coil are in your 80 gallon tank? How would you pipe two tanks together, for instance, an 80 gallon tank and the existing 40 gallon tank? Is it as simple as I think it is, just putting the outflow into the inflow on the second tank?
The cost difference for me isn't that great to make me really want to go through the headache of getting the tanks and getting them in the house and the headache of finding someone other than me to hook them up, if there is a qualified installer willing.
There are a lot of ifs in there for me to go with the pressurized storage. The unpressurized tanks take that out since they are ready made. They are light enough to carry into the house. I do worry about the complexities and the DHW. Not many installers are familiar with the pressurized storage as well. The unpressurized systems seem to be more common and so the installers are more familiar with them, and long term if anything goes wrong, a plumber or the installer will be able to help me out.
I wish there were kits for the pressurized systems utilizing old propane tanks for cost savings. It really sucks, but just finding an installer in my area that seems to understand these systems has been a headache in and of itself. I just have been beaten down so much by this process that the prospect of having to get two large propane tanks into my basement and the headache of finding a qualified installer willing to hook them up does not appeal to me. I am shocked at how few plumbing/heating professionals in Maine there are that are licnensed for solid fuels, and how few of them are familiar with wood gasifiers and willing to hook them up. This is technology that is not new, and really should be embraced. Its quite sad that Europe is kicking our butts on the prevalence of these systems. I'll get off my soap box now. This has turned out to be quite the message.
Leaddog you almost had me back on the pressurized bandwagon, but I just don't want to deal with the headaches. If two 500 gallon tanks fell on my lap, well I guess I might try harder to go that route. I am curious how you did it though with the 80 gallon tank. Any issues of DHW when the boiler isn't running? What temp of storage do you need to make the temp for hot water sufficient?