Hi all,
Well, the 30+ year old copper hot water tank for our combustion stove finally sprung a leak or five in the last week. Checked it out and there's lots of solder patches all over it already.... and a lot of green weep marks as well.
So! Time for a new tank. Don't know about where you are, but standard domestic hot water systems here are pretty much all mains-pressure, unvented types. I want a vented tank that's compatible with my stove and gravity fed system and has a heat-exchanger coil in it to run a pressurised hot water service for a shower. Trickier (and a lot more expensive) than it sounds to actually get one. It's also a tight spot in the cupboard behind the stove, and there's nowhere else to put it. There's about 6 or 7 foot of head when the main tank's full, hence the need to pressurise the shower to try and save water over the baths that we're having now.
I've decided to talk to a sheet metal maker about constructing one instead, either out of thin(ish) aluminium or galvanised sheet. Here's what I've got so far:
400x400x900mm tank, with a removable top sealed with 8 bolts and a gasket, giving approx 140 litres storage. It will be insulated with about 75mm of "pink batt" insulation all round,but more on the top half. For connections , it has:
- 1/2" BSP socket at top of tank for air vent connection.
- 3/4" BSP socket at bottom of tank for drain/ main water tank connection.
- 3/4" BSP socket near top of tank for stove hot water connection, probably 100mm down from the top.
- 3/4" BSP socket near bottom of tank for stove cold water connection, probably 100mm up from the bottom.
- 2 x 1/2" BSP sockets welded through the tank for the internal heat exchanger loop, one 50mm from the top of tank, one 200mm from top of tank.This, with the removable lid, gives the the opportunity to access and replace the copper loop when needed.The sockets are high up, so I can reach the internal fittings with the lid off.
- Copper heat exchanger loop, 3 meters or so of 1/2" copper, wound on a 300mm dia former, going from the bottom 1/2" socket down to the same level as the cold water connection to the stove (100mm up from bottom),then coiled back up to the top 1/2" socket.
Questions I have:
- Anyone got an idea of the "ideal" position of the stove's inlets and outlets? Eg. Do you have the top one lower down to give more "room" for warmer water above it? I presume the water in the wet back won't rise until it's warmer than the water at the tank, so if it's outlet is right at the top of the tank, will this mean circulation will slow once the water there gets hot? Should I lower the return a little to 3/4 of the way down the tank to give some room for the heated water to rise up out of the way?
Original tank takes all day to get the water up to enough temp for two quick baths at present, and I have to wonder if the thermosiphon is set up correctly. The wet back takes up about 300x150mm in the side wall of the firebox in the combustion stove. I would really like to improve on heating times, so I don't have to burn 1/2 ton of wood to have a shower. It was definitely an improvement after I insulated the bare metal tank(!!) a week after I arrived.... so the more insulation, the better I guess.
- Anyone see any fatal flaws?
Cheers
Dave