Unvented hot water.

[Matthew]

Hi All,

So the time has finally come. Actually staying in hotel last week with a fantastic shower was the last nail in the coffin for our pathetic gravity feed system. We are going to investigate the price of having a high pressure hot water system fitted. Ive had a look at the heatweb website and am starting to educate myself into the benefits of heat banks and megaflows. In our house (4 bed) we have 3 bathrooms which consist of one bath, three showers and three sinks plus the kitchen hot water (also 15 radiators). Its quite a big system. Does anybody have any experience of fitting these type of systems into an existing Yplan gravity feed system and what size of unit would be required. I would like to be knowledgeable when the prospective plumbers turn up to give me a quote for obvious reasons. Is it a major job?

BTW how would I know if the mains water was high enough in terms of pressure for use with such a system? Our mains riser in the kitchen comes in through a large bore pipe (70's house) and is stepped down straight away under the sink to 15mm for feeding the existing gravity system.

Thanks for any advice, Matthew

[Christian McArdle]

You need to measure the static pressure and the flow rate at the kitchen tap. Try it at several times of day, specifically including the morning "rush hour". You may have to contrive something to measure the pressure. In actuality, the flow rate is more important, although static pressure can be a good indicator of potential if you know the pipework to be well sized.

If all is OK, you will need a 210L (or thereabouts) unvented cylinder or heatbank. If you live with greater than average numbers of teenage girls, consider a slight upgrade.

Consider replacing the 15mm pipe with 22mm. Also consider running a dedicated 22mm line from the stop c*ck to the HWC/heat bank. The output from the heatbank should be in 15mm to reduce the hot water dead leg time and wastage, especially if your pressure is good.

Christian.

[The Natural Philosopher]

My bath is 500x1500x300mm deep. It takes 225 liters to fill it.

I have a 700 liter tank, and sometimes that isn't enough..

[Christian McArdle]

There is something wrong with your system if 700 litres won't fill a 225 litre bath.

Christian.

[Richard Conway]

Especially considering that you would expect some cold to be added as well

[Andrew Mawson]

Perhaps he's a serial bather

AWEM

[Christian McArdle]

With a decent boiler, this wouldn't matter, as it should be capable of entirely regenerating the bath full of water in about 22 minutes. The 700 litre tank would provide about 1100 litres of bath water without any regeneration at all, which is almost 5 of his oversized bath loads.

Christian.

[Dave Plowman (News)]

Chances are the hotel had a gravity fed system...

Before that could you re-site the header tank up higher? You'd be amazed how little extra height effects pressure if you're starting from near zero head.

[Ed Sirett]

Something wrong here...

1)The water in the bath is not pure HW so it will only consume around half that quantity of HW. 2) Your bath is sized like most peoples however when you get in it, you only need the water around you (as you will displace anything from 50-100 litres).

The received wisdom is that 70 litres of HW water needs to be stored per bathroom. (Obvious teenage mermaids and "celebs" taking "hollywood showers" make for a bit more still).

[Doctor Drivel]

Chances are it will not.

Will you please eff off as you are an idiot.

[Doctor Drivel]

Best go for a heat bank as unvented cylinders require an annual service of approx £100. Heat bank can operate at higher pressures, usually meaning good flows.

If having 15mm on the draw-offs, have a manifold at the heat bank, which means all the DHW draw-offs go back to the one point

[The Natural Philosopher]

It will only fill three of them.

[The Natural Philosopher]

You don;t know much about my bathing habits so you? OR about ,y wifes habit of leaving the kitchen sink hot tap running while she wanders around thinking about something else entirely...

[The Natural Philosopher]

Indeed I am.

[The Natural Philosopher]

I never let received wisdom get in the way of personal experience.

[Christian McArdle]

Wow, you like your baths at 60C? Even with a cold bit at the bottom of the cylinder, it should fill four.

If the only reason you need it so big is because your wife leaves the tap on, I'd go for a much smaller tank, as it will waste less energy and regenerate from cold quicker.

Christian.

[adder1969]

I used to have an unvented system and I was never required to have or to pay for a service.

Heat bank can operate at higher pressures, usually meaning

My unvented system was at 1bar pressure but it had a reasonable flow rate. My house now has a higher pressure but the flow is rubbish so that really needs to be checked before anyone starts fitting the mains fed systems.

[Doctor Drivel]

I used to have an unvented system and I was never required to have or to pay for a service.

[adder1969]

[Doctor Drivel]

The service "has" to undertaken by an "approved" unnted certificate installr. Thermal stores/heat banks can be DIYed and no annual service. Have a leak and if no service and proof of service then no insurance payout.

An unvented cylinder? Only an "approved" unvented certificate installer can install one. It is againt the law to fit one otherwise, unless signed off by a BCO.