Replacement hot water tank

Woot773 · 24-05-2023 12:52pm #1

Hi,

I currently have a standard vented hot water system with gas boiler, hot water tank and cold water storage tanks in the attic.

The tank is quite small (90L) and I need to replace it for a larger one in the short term, however I would like to keep some other options and longer term goals open!

I would like to consider including possible integration of a back boiler wood stove and would consider heat pumps once the insulation has been improved (and I have money...)

Would a typical twin or 3 coil vented cylinder be suitable or is something like a maxipod thermal store required?

Any help hugely appreciated!

antoinolachtnai · 24-05-2023 2:14pm

A thermal store is a different sort of thing from a hot water cylinder. I mean it looks the same and is made from similar materials but it’s a completely different setup.

You really need someone to design a solution for you and stand over it. If budget is an issue I would recommend keeping it really really simple. A triple coil cylinder could be set up to allow you heat water really fast from your boiler and might be a good investment if your hot water is running out at times. backboiler wood burning stoves are expensive for what they offer. Maybe you would be better off putting money away towards the big project.

I presume you mean ‘vented’ rather than ‘unvented’ cylinder. Vented is the standard thing.

Woot773 · 24-05-2023 3:05pm

https://www.boards.ie/discussion/comment/120635605#Comment_120635605

Thanks for the advice, can barely get a shower out of the current hot water tank, so an increase in size will be essential. There is also no thermostat installed on the cylinder so the temperature can only be controlled with time programming...

The only reason I mentioned the back burner is that we do burn alot of wood (heat and ambience) and the stove is relatively close to the cylinder (assuming the back boiler is connected to the cylinder and not in series with the rads). If I could buy a cylinder that can accommodate multiple heat sources it would appear to make sense?

And yes, you're correct, I currently have a vented system (typo).

Cheers

antoinolachtnai · 24-05-2023 3:47pm

You can install a stat on any cylinder. You might as well do that now. Once you have that you could leave boiler on during peak shower time and it might alleviate the water shortage a little bit. It’s mainly a matter of running the cable and wiring

A stove hookup is going to cost a lot, realistically around the same cost as a replacement gas boiler.

If you aren’t under time pressure I guess it will be worth your while ordering a cylinder to that sort of spec. You can always use the extra coils to give faster recovery (Re-heating) of the tank. But you need to talk it through with the plumber.

monseiur · 24-05-2023 3:50pm

Firstly you need an open vented system for the following. Fit a cylinder with two coils, one for the gas boiler and a spare for future solar thermal panels on roof. Plumb the cylinder directly to wood stove, the water basically flows directly from cylinder to stove and heats up, is pushed by gravity back into cylinder, no pump required. If the house is occupied during the day (to stoke the fire!) you'll have gallons of hot water for domestic use especially during autumn, winter early spring even the following morning with a well lagged cylinder.

During a warm spell in summer when stove fire is not required use the gas to heat domestic water or alternatively you may fit an immersion in the cylinder for this purpose.

Forget heat pumps, they just don't work when retrofitted, don't listen to snake oil salesmen or some delusional greens..unless of course you have a budget of over €120,000 !

aero2k · 24-05-2023 3:57pm

https://www.boards.ie/discussion/comment/120635988#Comment_120635988

Could you elaborate on the final paragraph in your post please? I had one installed as a retrofit last Sept and it appears to work well, albeit with a lower COP than the claimed 4 (I am just under 3 I think). I haven't yet upgraded my windows but I expect it will work even better when that's done. Heatgeeks have lots of videos on youtube (no connection to them) explaining how they can work well even in old houses.

OP sorry for the hijack.

10-10-20 · 24-05-2023 4:05pm

https://www.boards.ie/discussion/comment/120636024#Comment_120636024

And a valid hijack it is too. I think what @monsieur might have meant is that HPs don't work on all retrofitted properties as there are cases where they are working.

antoinolachtnai · 24-05-2023 4:18pm

plumbing in backboilers can be done but it is important to do it right. There are a lot of safety considerations. It’s a whole different thing from plumbing a gas boiler

I don’t know if there is much point in solar thermal anymore, especially if the house is occupied all day. PV is probably a better investment if you want to put stuff on the roof. Makes sense to have a coil you can connect the gas boiler to, certainly.

a well functioning wood stove will cost thousands a year in transport, labour and fuel, and far more than €120,000 over its life.

in the end it’s a matter of finding what you will be happy with. There is no magic solution.

Woot773 · 24-05-2023 4:52pm

https://www.boards.ie/discussion/comment/120635988#Comment_120635988

That's an interesting option, any issues with having the potable water cycle through the back boiler? (I assume not if the pipework is clean). It does appear that when the fire is not in use there will be significant heat loss from the pipes unless there are valves to isolate the circuit - which would get explosive if you forget to open the valve and boil the water in the back boiler pipes...

aero2k · 25-05-2023 9:57am

https://www.boards.ie/discussion/comment/120636052#Comment_120636052

To be fair to monsieur, a lot of the suppliers, including the one I used, are really sales and not technically focussed. There's a complete change in mindset needed particularly if you're used to getting 3rd-degree burns from your rads😀. Also my house was built in 2001 and has the cavity pumped with beads, so not a bad starting point. But they can work well if properly designed and installed.

monseiur · 25-05-2023 10:31am

https://www.boards.ie/discussion/comment/120636222#Comment_120636222

Potable water should come directly from rising mains, not from attic storage tank. But hot water from cylinder will be OK for cooking, to wash/prepare veg etc. and for all other domestic use. The only minor issue you may have (depending on stove's boiler output) is cylinder over heating at times (cylinder banging) - if no hot water is being drawn for a long period. Problem easily solved by running hot tap. Under no circumstances should isolating valves be fitted on pipes between back boiler & cylinder, obviously same applies to the vent pipe. The heat loss when stove is not in use is negligible and any minor loss will be compensated for by stove in the long run.

If you have you own supply of timer or access to cheap fuel a stove is a very economical way to heat domestic water, heat kitchen/dining area and of course do all cooking etc. ... even during a prolonged power cut provided of course that water supply is not cut off.

Replacement hot water tank

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