C
conrad
Hi,
I'm in a one-floor flat, currently with a cold water tank about 4 foot above floor level and an electric immersion tank underneath it at floor level (no gas, Economy 10 electricity). This obviously is a disaster for anything except a bath: there's a shower hose attached to the bath taps, but you can't stand up and get hot water. I'm looking at re-engineering the hot water system. The two options appear to be an unvented hot water cylinder and a thermal store (both electric: again, there's no gas here). The cold water pressure is good I think: don't know how to measure it, but I get 40 litres a minute out of the cold tap. The local water (Edinburgh) is probably the softest you can get. The building is listed, converted to "modern" habitation in the 70s, and as far as I can tell has plastic stacks, which is a bit of an issue re: unvented system --- my understanding is that I need metal pipes to ground level for that. It's not impossible: while replacing the interior drain might be unfeasible, there's a plastic drainpipe from the gutters just outside the bathroom which I might be able to replace with cast iron.
So my question is, what are the considerations between an unvented system and a thermal store? Looking at the specs for thermal stores, I typically see "limit 20 litres per minute", much lower than my cold tap; also it seems to me that where with a hot water cylinder that you draw from directly, you'd expect that until the cylinder runs out of hot water you'll get just hot water. However with a thermal store you'll be reducing its temperature all the time you use it, so its output water will get steadily cooler with use --- a bit like the difference between certain kinds of rechargeable battery: sudden death vs gradual decay. I think I prefer the idea of a shower which works well until it doesn't, to the idea of one which gets steadily worse from the moment you start using it. That said, the annual maintenance cost associated with unvented seems a fairly big negative. Anybody in a position to compare and contrast from personal experience?
Conrad
I'm in a one-floor flat, currently with a cold water tank about 4 foot above floor level and an electric immersion tank underneath it at floor level (no gas, Economy 10 electricity). This obviously is a disaster for anything except a bath: there's a shower hose attached to the bath taps, but you can't stand up and get hot water. I'm looking at re-engineering the hot water system. The two options appear to be an unvented hot water cylinder and a thermal store (both electric: again, there's no gas here). The cold water pressure is good I think: don't know how to measure it, but I get 40 litres a minute out of the cold tap. The local water (Edinburgh) is probably the softest you can get. The building is listed, converted to "modern" habitation in the 70s, and as far as I can tell has plastic stacks, which is a bit of an issue re: unvented system --- my understanding is that I need metal pipes to ground level for that. It's not impossible: while replacing the interior drain might be unfeasible, there's a plastic drainpipe from the gutters just outside the bathroom which I might be able to replace with cast iron.
So my question is, what are the considerations between an unvented system and a thermal store? Looking at the specs for thermal stores, I typically see "limit 20 litres per minute", much lower than my cold tap; also it seems to me that where with a hot water cylinder that you draw from directly, you'd expect that until the cylinder runs out of hot water you'll get just hot water. However with a thermal store you'll be reducing its temperature all the time you use it, so its output water will get steadily cooler with use --- a bit like the difference between certain kinds of rechargeable battery: sudden death vs gradual decay. I think I prefer the idea of a shower which works well until it doesn't, to the idea of one which gets steadily worse from the moment you start using it. That said, the annual maintenance cost associated with unvented seems a fairly big negative. Anybody in a position to compare and contrast from personal experience?
Conrad
