Best heating system for low pressure mains?

[RickyLee53]

Hello,

I'm in the middle of my house renovation, at the moment we have average/poor mains pressure/flow. While building an extension we had to "move" the mains supply, it is lead and kinked/damaged, so I am hoping this is partly the problem, and it will be solved when we run a new large bore MDPE pipe to the house from the street.

However, I am currently spec'ing the bathroom, and the bath we want is 460L capacity. Also the shower is a 400mm x 400mm head.

There are 2 other rooms with ensuites, neither have baths and I suppose we could deal with an electric shower in 1 of them.

I was thinking of a large unvented cylinder. But obviously I want something with a high recovery rate for when we fill the bath. I also need high pressure/flow for filling the bath.

Is there any way to boost the pressure higher than the cold flow?

 

[swbjackson]

I'd wait and see what happens when you get the main replaced first. If it's insufficient look at getting a booster set.

Have a look at http://www.lowara.co.uk/booster-pum...d)-booster-set-for-domestic-dwellings_P47199/

I recently fitted a resfix for a customer and it's a really nice bit of kit.

 

[Agile]

I hope you can afford all the water for a 460 litre bath and a 400 x 400 shower.

Although showers are rated on their flow rate not the size of the head!

Tony

 

[flameport]

the bath we want is 460L capacity.

The total capacity of the bath is not really relevant, because people do not fill their bath to the top or anywhere near it, and baths are not filled with 100% hot water either.

Is there any way to boost the pressure higher than the cold flow?

Flow and pressure are different things. There are ways of increasing both, but useless to consider this until you know what the flow and pressure from your new supply will be.

 

[simond]

A 400 litre bath is going to be very wasteful. Unless you weigh 25 stone (archimedes theorum).

As above there are all sorts of ways of boosting flow, but until you take some measurements you are peeing in the wind.

 

[transam]

400x400 shower head , capable of chucking out what ? a minute ?

shallow , shower tray ?? thought about the waste/ drain ? 42mm waste pipe ??

 

[RickyLee53]

I hope you can afford all the water for a 460 litre bath and a 400 x 400 shower.

Although showers are rated on their flow rate not the size of the head!

Tony

I see your point and appreciate the advice. I'm not too concerned about the cost, I/we only take a bath once in a while and it might as well be a nice experience. A very rough calc i've just done would say its going to cost approx 50p per bath. The spec says 460 litre. I don't know how full that is.

I'd wait and see what happens when you get the main replaced first. If it's insufficient look at getting a booster set.

Have a look at http://www.lowara.co.uk/booster-pum...d)-booster-set-for-domestic-dwellings_P47199/

I recently fitted a resfix for a customer and it's a really nice bit of kit.

Good point, however. I'm ordering my bathroom in the next couple of weeks. But cannot change the incoming supply for probably 6-7 weeks. Hence wanting to know if I do have an issue with the time it takes to fill the bath. Or the flow rate of the shower head then I can do something.

 

[RickyLee53]

400x400 shower head , capable of chucking out what ? a minute ?

shallow , shower tray ?? thought about the waste/ drain ? 42mm waste pipe ??

It is going in a wet room. Thats the main head, there will be a "normal" sized shower head as well. Waste will be a long grid. I'm not sure on the waste pipe yet. But I don't think 42mm will be sufficient.

A 400 litre bath is going to be very wasteful. Unless you weigh 25 stone (archimedes theorum).

As above there are all sorts of ways of boosting flow, but until you take some measurements you are peeing in the wind.

The bath can fit 2 people in. Although I doubt the Mrs would happily bath in my water! I'm 16 stone, and our current "slipper bath" results in more water on the floor than in the bath. Less of Achimedes theorum, More Newtons third law though.

 

[RickyLee53]

I'd wait and see what happens when you get the main replaced first. If it's insufficient look at getting a booster set.

Have a look at http://www.lowara.co.uk/booster-pum...d)-booster-set-for-domestic-dwellings_P47199/

I recently fitted a resfix for a customer and it's a really nice bit of kit.

I've just had a look at the link. Can this be used in conjunction with a normal cold storage tank? It says upto 60l/minute at 4 bar pressure for the biggest unit. Providing its safe to put before an unvented cylinder. (I can't see why not)

Any idea of the cost of the boosters?

 

[RickyLee53]

Right,

I've just done a test (as you can tell i'm clearly not a plumber) but know about flow rates and its relationship with pressure.

I'm not sure if the test is any use but i'll explain what I did and maybe somebody can use the information and help.

I tested the static pressure. (by this I mean I connected a pressure gage to a cold water tap feed and read the pressure) To my surprise the pressure gauge read 3.6 bar.
I also tested the flow rate, to my disappointment the flow rate of a downstairs cold water tap is 6 litres per minute!

So. I left the pressure gauge on and turned on the taps upstairs. The pressure dropped off to 0.4 bar!

I'm not sure how a normal "dynamic" (if thats the term used in plumbing) pressure/flow test is carried out but at least we have some figures to work with now.

Obviously the pressure is what I would gather to be fairly good, but the pressure drop is HUGE. In theory if I run a new mains supply to the road in the largest bore possible pipe, then get them to connect it I should be laughing, without the need for the booster.

But the question is what is the largest bore I can get them to connect?

The current feed pipe is lead, probably 15mm internal bore and runs around 50 meters to get into the rear of the house. Friction losses must be very high, along with repairs/kinks etc. My new pipe will be only 10 meters long and entering the front of the house. But obviously from there I will have pipe running in the cellar so i'll have to expect some pressure drop/decreased flow due to friction losses and obviously the bathroom is approx 3m higher so another 0.3 bar or so lost there anyway.

 

[CBF]

unless you can increase the flow rate & pressure (which unless you have some major friction losses in your existing pipe the pressure isn't going to change much even with a new supply & standing pressure means nothing it's working pressure that matters) i wouldn't even be considering an unvented or combi, neither will work on 0.4 bar & as soon as you turn on a tap downstairs upstairs will stop completely, i still say go roof tanks & vented cylinder that way you can use a pump to boost your bathroom & thermostatic shower.

 

[RickyLee53]

If I have 3.5 bar static. Surely all I have is friction losses. If the pressure is there to start with and flow reduces it then it should all be pressure drop because of the pipes. It takes 2-3 seconds to recover to 3.5 bar after the tap has been on. It also takes around a second for the pressure to drop to 0.5 bar.

Edit. I've just been thinking about it.

By doing the test how I am what I am actually measuring is the friction resistance of the pipes between the upstairs and downstairs and the head of approx 2.5 meters. to be 0.5 bar. Which would seem about right.


I did a calculation of the pressure drop down 50 meters of 15mm at 25l per minute i'd lose 2 bar.

Then on the approx 15m to the bathroom i'd lose a further 0.6 bar. But this doesn't take into account bends etc.

The above is still 3 x the flow I actually have, and I'm measuring the pressure roughly 5 meters from where the mains comes in. But at roughly the same head height.

So I think its safe to say i'm losing all the pressure enroute to the house, and the lead pipe has further damage/a kink.

unless you can increase the flow rate & pressure (which unless you have some major friction losses in your existing pipe the pressure isn't going to change much even with a new supply & standing pressure means nothing it's working pressure that matters) i wouldn't even be considering an unvented or combi, neither will work on 0.4 bar & as soon as you turn on a tap downstairs upstairs will stop completely, i still say go roof tanks & vented cylinder that way you can use a pump to boost your bathroom & thermostatic shower.

 

[Dan Robinson]

So, you'll need to look at replacing the main. Which is not a bad idea anyway if its lead.

Or look at the break tank and booster set mentioned before - or possibly an accumulator.

I wouldn't ignore CBF's idea either. But can't remember the last OV domestic system I fitted its so "Victorian"

 

[RickyLee53]

So, you'll need to look at replacing the main. Which is not a bad idea anyway if its lead.

Or look at the break tank and booster set mentioned before - or possibly an accumulator.

I wouldn't ignore CBF's idea either. But can't remember the last OV domestic system I fitted its so "Victorian"

Thanks for the input.

The main purpose of this thread was so I can order the huge bath and shower, and if replacing the main doesn't give desired results I can do something else. I'll certainly replace the main first then I can look at boosting if it still isn't sufficient.

Am I right in thinking if I install a booster pump I need some kind of tank as well. Surely without you'll just get cavitation.

Edit, i've just reread the above post by CBF. Surely i'd be better with an unvented cylinder with a pump before it. Rather than a vented with the pump after it? Both for pump reliability and cavitation reasons.

 

[CBF]

i agree Dan however i think of it this way, how many houses out there have a vented cylinder & the customer needs a new boiler & is thinking about a combi only for us to say no i wouldn't recommend that because your water flow rate or pressure isn't good enough, so therefore why should a new system be any different ? if the house hasn't got the req pressure or flow then roof tank & ov cylinder is the only way to go, don't forget the water co's are reducing the mains supply pressures due to their leaking supply pipes, when did the combi manifacturers ever tell you to remove their flow rate discs due to a flow rate issue but they do now.

OP, you can't pump the mains anymore than 12 ltrs/min (there is a new booster pump on sale now that does comply with this), so a booster pump on the main isn't going to solve your problem if you go unvented, but if you go my route then you can fit a 4 bar twin ended pump to feed your bathroom & shower, of course the roof tank & cylinder must be sized correctly, like i said static pressure means nothing if the working pressure goes down to nearly nothing.