Under sink water heaters

[marshman]

__

[dangermouse]

Well it's been a while, but I finally got round to posting an update on this.

I went ahead with my under sink water heater plan. In the end I got a "Hyco SpeedFlow stainless steel" with 10L capacity. "Must be fitted by a qualified person", so um, yeah, I fitted it myself. It's not complicated and nothing has exploded yet.

I got the 1.2kW version as my inverter is 3.6kW so this reduces the chance of drawing from the grid if a few appliances are turned on, at the expense of not heating as quickly, obviously. The heater is plugged in to a 13A socket via a timer switch that turns it off at 11pm and back on at 6am. Takes about 20 minutes to heat to around 60C.



The slightly complicated pipework is because I fitted a couple of ball valves that allow me to isolate the electric heater and reconnect the hot water feed from the gas combi boiler. My thinking is this might be handy in winter when solar power is limited.

In the centre of the photo you can see the pressure relief valve (behind the sink waste pipe) that feeds into a tundish connected to an unused waste outlet (was used for a dishwasher). Also teed off from the cold water inlet to the heater is the 2L expansion vessel, which is secured in place by a piece of old motorcycle inner tube screwed to the cupboard wall

After running this for a couple of months, I can happily say it is definitely worth it. Sadly I haven't got "before and after" gas usage figures, but over the sunny months I've spent virtually nothing on grid electricity so this heater has been happily using some of the surplus I would have otherwise exported (for free). It's great to have instant hot water without having to wait for the boiler to heat up.

If I could change anything, I'd go for the 15L model, as 10L isn't quite enough to do a large batch of washing up, but I've adapated my habits and just do the washing up in more, smaller, batches. I wasn't sure if the 15L model would have fit in the space available (you can see the dimensions I meaasured drawn on the cupboard) but with hindsight I think it would. I might move this one to the bathroom and get a larger one for the kitchen. But that's for another day.

[spread-tee]

Nice neat install there mate, particularly like the neat end feed copper work. The only thing I don't reckon are those flexi hoses, I know they are supplied with the kit but they are not good in the long term, I can see you have been gentle with the radii but still...... Over the years I have replaced thousands of them because they are fraying or leaking and worse. A rigid copper connection is far better IMHO or if you really want some flex go for "Polyplumb"! or similar.

Desp

[Stinsy]

Well it's been a while, but I finally got round to posting an update on this.

I went ahead with my under sink water heater plan. In the end I got a "Hyco SpeedFlow stainless steel" with 10L capacity. "Must be fitted by a qualified person", so um, yeah, I fitted it myself. It's not complicated and nothing has exploded yet.

I got the 1.2kW version as my inverter is 3.6kW so this reduces the chance of drawing from the grid if a few appliances are turned on, at the expense of not heating as quickly, obviously. The heater is plugged in to a 13A socket via a timer switch that turns it off at 11pm and back on at 6am. Takes about 20 minutes to heat to around 60C.



The slightly complicated pipework is because I fitted a couple of ball valves that allow me to isolate the electric heater and reconnect the hot water feed from the gas combi boiler. My thinking is this might be handy in winter when solar power is limited.

In the centre of the photo you can see the pressure relief valve (behind the sink waste pipe) that feeds into a tundish connected to an unused waste outlet (was used for a dishwasher). Also teed off from the cold water inlet to the heater is the 2L expansion vessel, which is secured in place by a piece of old motorcycle inner tube screwed to the cupboard wall

After running this for a couple of months, I can happily say it is definitely worth it. Sadly I haven't got "before and after" gas usage figures, but over the sunny months I've spent virtually nothing on grid electricity so this heater has been happily using some of the surplus I would have otherwise exported (for free). It's great to have instant hot water without having to wait for the boiler to heat up.

If I could change anything, I'd go for the 15L model, as 10L isn't quite enough to do a large batch of washing up, but I've adapated my habits and just do the washing up in more, smaller, batches. I wasn't sure if the 15L model would have fit in the space available (you can see the dimensions I meaasured drawn on the cupboard) but with hindsight I think it would. I might move this one to the bathroom and get a larger one for the kitchen. But that's for another day.

Thanks for the post. Looks like a nice install. We use water from the boiling tap for washing up instead of from the combi all the way in the attic. If we had room for one of these I’d have one.

I am interested in the pressure relief valve. Is it incase the heater fails with the heating element on and starts boiling?

[dangermouse]

Thanks for the comments.

The flexi hoses didn't come with the heater but the instructions said to use them, so I got them from Screwfix. It does give the flexibility (ha) to move the heater slightly in the cupboard if required - it's not fixed down at all just free standing. I'll keep an eye on them though and if they give problems I'll investigate "polyplumb".

The cold inlet to the heater is connected straight to the mains supply, with the expansion vessel and relief valve teed off that feed. There's also a one way valve in that feed to stop water from the heater flowing back into the mains supply. Again, following the instructions, it says if you have a certain length of pipe (over about 4m I think) you don't need an expansion vessel as the pipework can accommodate the expansion, but for mine it's less than 1m.

As the water heats and expands it's got to go somewhere, and the relief valve is in case the expansion vessel can't handle this. So yes, a possible failure mode is that the thermostat fails and the water boils, in this case you'd get hot water venting into the waste pipe via the tundish.

The tundish has a one way valve in it as well (just a spring loaded flap) that prevents waste water from the sink escaping, not that I think it would due to the vertical orientation.

[resybaby]

Couple of points to make with this one that relate to my previous day job as a Water Regulations Enforcment Officer.

1. The waste pipe you vent the pressure relief valve into (via the tundish) needs to be able to take water/steam at 100'c under fault conditions. Normal plastic waste pipe isnt sufficient. So change for 22mm copper all after the tundish, and ensures it runs downhill all the way to a conspicuous safe drain point outside (turned back to the wall with a metal cage, or a drain gully etc). Keep'it separaten from any sink/wash mc drainage.

2. You say the tundish has a "one way valve" within it?
Having any obstruction in a expansion or pressure relief pipe from an unvented system like yours doesnt comply with the G3 building regulations. It is dangerous and need replacing.
The idea of the pressure relief pipe is to get rid of the water under fault conditions without any hindersnce or obstruction of any kind i.e. faster and not reliant of mechanicl parts wherever possible in case they fail. Open pipe is the best. There are restrictions on pipe lengths and numbers of bends, but shouldnt apply to your install assuming your install is on an outside wall, and you dont make the pipe up with a box full of elbows.

3. Flex hoses are ok in such installs, in fact sometimes totally neccasary through lack of space for hard piping, us plumbers are often big lads! no legal requirement, but a good idea to fit isolators if you havent on those.

Rex