Under-bench hot water cylinder.

Forums › Home Workshop DIY › Under-bench hot water cylinder.

Resnick

238 posts

Master Geek

Lifetime subscriber

#230554 1-Mar-2018 09:43

Morning all;

We are (thankfully) towards the end of a kitchen upgrade. Up to now there has been an electric Rheem 25L underbench hot water cylinder supplying the kitchen sink. The remainder of the house is on a gas infinity system and due to the layout there would be an unacceptably longish lag time before hot water would reach the kitchen sink.

The 25L Rheem cylinder is probably 10-12 years old although it appears to be working just fine. I'm thinking that it is probably towards the end of it's working life and should be replaced now that we are getting a plumber in.

Is this a sensible thing to do at this point? And does anyone have experience with small instant / tankless electric hot water systems that would be a suitable alternative?

Thanks in advance.

1 | 2

8328 posts

Uber Geek

#1966350 1-Mar-2018 09:52

Electric "tankless" hotwater is in all reality a joke. The flowrates are pathetic..

If your primary use is just washing hands, you might get away with it, but the start up time will mean that it is still slower than your current tanked system,

If you are filling sinks on a regular basis to wash things, keep your tank....

nickb800

2719 posts

Uber Geek

Trusted

#1966377 1-Mar-2018 10:08

I have lived with a tankless electric HW shower before, low rate but bearable (perhaps 7l/min, similar to the most eco of showerheads).

If you have/use a dishwasher then it may be okay, otherwise as above you'll hate filling up the sink.

Other thing to bear in mind is that instant electric HW requires a dedicated high current mains electricity feed, which may be expensive if it's a long way from your switchboard, and may cause issues with overall capacity if you already have a lot of high current circuits (e.g. induction hob, spa)

scuwp

3885 posts

Uber Geek

#1966387 1-Mar-2018 10:23

Wow, must be a huge house and you must be extremely busy if the few seconds it takes for hot water to reach the tap from the Infinity system is that unbearable. If it were me I wouldn't hesitate connecting it up to the gas system.

Lazy is such an ugly word, I prefer to call it selective participation

timmmay

20582 posts

Uber Geek

Trusted

Lifetime subscriber

#1966399 1-Mar-2018 10:47

scuwp:

Wow, must be a huge house and you must be extremely busy if the few seconds it takes for hot water to reach the tap from the Infinity system is that unbearable. If it were me I wouldn't hesitate connecting it up to the gas system.

In my place it can take 10 seconds or more for hot water to reach taps at the far end of the house. That wastes water and power, but possibly less expensive than having to have and heat a second cylinder.

nickb800

2719 posts

Uber Geek

Trusted

#1966400 1-Mar-2018 10:48

scuwp:

Wow, must be a huge house and you must be extremely busy if the few seconds it takes for hot water to reach the tap from the Infinity system is that unbearable. If it were me I wouldn't hesitate connecting it up to the gas system.

It's a pretty standard arrangement to have a separate HW system for the kitchen when it's far from the main HW system. You can loose a lot of heat over a long run, so may even be financially worthwhile to have a second HW system if there is significant use of HW

davidcole

6036 posts

Uber Geek

Trusted

#1966406 1-Mar-2018 10:52

timmmay:

scuwp:

Wow, must be a huge house and you must be extremely busy if the few seconds it takes for hot water to reach the tap from the Infinity system is that unbearable. If it were me I wouldn't hesitate connecting it up to the gas system.

In my place it can take 10 seconds or more for hot water to reach taps at the far end of the house. That wastes water and power, but possibly less expensive than having to have and heat a second cylinder.

We have this with our infinity and master ensuite. When we moved in there were 3 hotwater cylinders, including one in a roof - We replaced with a single infinity but knowing it was add delay....but I'm planning on putting in a second infinity for this....apart from the install costs, you're not storing hot water all the place.

Previously known as psycik

Home Assistant: Gigabyte AMD A8 Brix, Home Assistant with Aeotech ZWave Controller, Raspberry PI, Wemos D1 Mini, Zwave, Shelly Humidity and Temperature sensors
Media:Chromecast v2, ATV4 4k, ATV4, HDHomeRun Dual
Server Host Plex Server 3x3TB, 4x4TB using MergerFS, Samsung 850 evo 512 GB SSD, Proxmox Server with 1xW10, 2xUbuntu 22.04 LTS, Backblaze Backups, usenetprime.com fastmail.com Sharesies Trakt.TV Sharesight

Resnick

238 posts

Master Geek

Lifetime subscriber

#1966407 1-Mar-2018 10:54

scuwp:

Wow, must be a huge house and you must be extremely busy if the few seconds it takes for hot water to reach the tap from the Infinity system is that unbearable. If it were me I wouldn't hesitate connecting it up to the gas system.

Others have already answered, and I'd like to add we are on tank water so draining 20L or more of water to get a hot flow isn't acceptable.

Quic Broadband

Move to New Zealand's best fibre broadband service (affiliate link). Free setup code: R587125ERQ6VE. Note that to use Quic Broadband you must be comfortable with configuring your own router.

Resnick

238 posts

Master Geek

Lifetime subscriber

#1966409 1-Mar-2018 10:57

Thanks for the replies so far, I'll be sticking with an underbench cylinder.

Should I just bite the bullet and get a new one or see what life I can squeeze out of the old one?

Suckerpunch

124 posts

Master Geek

#1966411 1-Mar-2018 10:58

We were in the same situation and decided that having the extra cupboard space in the kitchen was more valuable then the time to wait for hot water to get to the kitchen tap. Our wait time is now 40 seconds, but the space is still as valuable as we predicted it would be.

Not to mention we no longer have to worry about replacing a hot water cylinder in 10-20 years time, in an hard to reach spot without ripping parts of the kitchen out.

Resnick

238 posts

Master Geek

Lifetime subscriber

#1966416 1-Mar-2018 11:02

Suckerpunch:

We were in the same situation and decided that having the extra cupboard space in the kitchen was more valuable then the time to wait for hot water to get to the kitchen tap. Our wait time is now 40 seconds, but the space is still as valuable as we predicted it would be.

Yeah, I had the same thought. Unfortunately there is only a cold water feed through a concrete pad surrounded by underfloor heating. I didn't even bother getting a quote for the costs involved plumbing in a hot feed!

timmmay

20582 posts

Uber Geek

Trusted

Lifetime subscriber

#1966429 1-Mar-2018 11:30

Low pressure hot water cylinders have a lifespan around 20 years according to this article. It probably has quite a few years left in it. However you need to weigh up the cost of a new cylinder (around $700 retail for a high pressure cylinder but you may be able to get a better price) against the hassle of having it fail in 5-15 years and having it replaced then.

Personally I'd probably not bother.

Amosnz

567 posts

Ultimate Geek

Lifetime subscriber

#1966431 1-Mar-2018 11:32

Heatworks have had a couple of different models that looked interesting, they originally started on kickstarter with the model1. Their latest one isn't available yet but might be worth book marking if the cylinder will live on for a while.

https://myheatworks.com/pages/model-3-specs

Speedtest

Resnick

238 posts

Master Geek

Lifetime subscriber

#1966445 1-Mar-2018 12:03

Thank-you all for your help and insights. I'll be re-installing the old cylinder and hoping for a good few more years out of it.

Much appreciated.

Edit: re-installing, not replacing

nickb800

2719 posts

Uber Geek

Trusted

#1966487 1-Mar-2018 13:37

Also check what is involved with replacing it - you don't want to have to rip apart your kitchen in 3 years if the cylinder fails - that might sway things in favour of a new cylinder now

JeremyNzl

359 posts

Ultimate Geek

#1966517 1-Mar-2018 14:20

We recently did up a building used for seasonal staff accom,

We removed a 25L cylinder in the kitchen and fitted, a variation of the instaboil that has some retained insulated storage, 2-5L

So basically its mini undersink version of the 25L cylinder,

However due to water expansion when heating it required a special tap to vent an excees expansion.

Flow rate seems decent and enough to do a sink of dishes per time if required.

Also its mounted to the wall under the sink so no cleaning issues behind a cylinder.

Cheers J

1 | 2