Changing boiler setup from vented to sealed tank - power shower pressure.....

[k13wjd]

Simple question really, will removing my power shower result in better or worse performance, boiler/hw tank changes below

Old setup : 24kw floor standing heat only boiler, vented HW tank bed by cold tank, around .75 bar head. Power shower has it's own 15mm output from the HW tank, and it's own 15mm cold feed from the cold tank. Pump rated to 1.6 bar(double ended motor type).

New setup : 30kw system boiler, sealed HW tank. House has cold water incoming 25mm mdpe, to 22mm cooper feeding hw tank. Shower now direct fed from HW tank, and direct fed from cold feed.

as long as the mains water pressure is greater than 1.6bar, the shower should be the same as before? Effectively it's fed with pressure via a 22mm single pipe, split into 15mm hot and cold by way of a big tank. Both 15mm pipes at the shower mixer should still be 1.6bar or above?

 

[DP]

as long as the mains water pressure is greater than 1.6bar, the shower should be the same as before? Effectively it's fed with pressure via a 22mm single pipe, split into 15mm hot and cold by way of a big tank. Both 15mm pipes at the shower mixer should still be 1.6bar or above?

The pressure reducing valve on the cold pipe to cylinder often regulates pressure to 3.5 bar
The theory is, if the mains is higher pressure, all the outlet should maintain good pressure.
What boiler do you have? What do you intend getting. How old is present instal

 

[Madrab]

as long as the mains water pressure is greater than 1.6bar, the shower should be the same as before?

Doesn't really work that way - there is a min dynamic pressure and flow that is really preferred for an unvented system to work properly, > 2.5bar @ 20L/Min.

You need to have your mains tested first - connect a pressure gauge to a full flow outlet like and outside tap and then run at least 2 other taps whilst filling a bucket timed over a minute. Then measure how much water has been gathered and note what water pressure there was. That will give you a starting point.

A 30Kw system boiler is poss too big - How many rads do you have and what's their average size/type?

 

[k13wjd]

The pressure reducing valve on the cold pipe to cylinder often regulates pressure to 3.5 bar
The theory is, if the mains is higher pressure, all the outlet should maintain good pressure.
What boiler do you have? What do you intend getting. How old is present instal

It's a 35ish year old ideal Mexico heat only. Likely putting in a Worcester Bosch 8000 system. Relocated as the flue run is absolutely nuts in the old system. Walls put in after the boiler at a guess!

 

[k13wjd]

Doesn't really work that way - there is a min dynamic pressure and flow that is really preferred for an unvented system to work properly, > 2.5bar @ 20L/Min.

You need to have your mains tested first - connect a pressure gauge to a full flow outlet like and outside tap and then run at least 2 other taps whilst filling a bucket timed over a minute. Then measure how much water has been gathered and note what water pressure there was. That will give you a starting point.

A 30Kw system boiler is poss too big - How many rads do you have and what's their average size/type?

15 I think. Varying in size from small bathroom/airing cupboard size, so some of the longest doubles I've seen. Like 3m long, but 30cm tall.....

It's a big house which isn't particularly energy efficient simply by design, with little option for upgrading relevant insulation.

I'll try and get a mains pressure reading today and do some flow testing.


The other option is to stay heat only/vented of course.

 

[Madrab]

What you want to do is log each size and type - then do a comparison on line as to it's output in Kw and then total that up and add 10%, that will give a guide as to the size of boiler you should be looking at. Given you have a 24kw in place and if that is currently suitable then any reason to change that? You could just upgrade the HW systems if the mains allows it and you really want an upgrade.

Unless the current system is failing or getting EOL, then of course what you have is perfectly acceptable

 

[fixitflav]

Simple question really, will removing my power shower result in better or worse performance, boiler/hw tank changes below

Old setup : 24kw floor standing heat only boiler, vented HW tank bed by cold tank, around .75 bar head. Power shower has it's own 15mm output from the HW tank, and it's own 15mm cold feed from the cold tank. Pump rated to 1.6 bar(double ended motor type).

New setup : 30kw system boiler, sealed HW tank. House has cold water incoming 25mm mdpe, to 22mm cooper feeding hw tank. Shower now direct fed from HW tank, and direct fed from cold feed.

as long as the mains water pressure is greater than 1.6bar, the shower should be the same as before? Effectively it's fed with pressure via a 22mm single pipe, split into 15mm hot and cold by way of a big tank. Both 15mm pipes at the shower mixer should still be 1.6bar or above?

Unless you have a big place, 24 kW is probably oversized, never mind 30. Is there any reason to think the current one struggles?

Where is the 0.75 bar measured? If it's at the level of the shower head that would give a good shower by gravity. I have more like 0.15 bar and it gives a perfectly adequate shower.

 

[k13wjd]

It is a big house, no question about that. There are some huge spaces to heat, and like only a quarter of the roof pitch can be insulated, the rest is vaulted.

I'm saying it's 0.75bar if head pressure feeding the DHW side, based on the height of the cold tank. The power shower pump is probably 1.5 bar.

The boilers I've been looking at start at 30kw output.....so unless I start looking at a (probably) lower quality, then 30kw it is!

 

[ericmark]

OK I do not live in Scotland, I live in Mid Wales, I have a 20 kW boiler (oil) and a house with 5 bedrooms, two living rooms, a dinning room, two kitchens, three bathrooms spread over three floors and the boiler still cycles off/on so clearly has not run out of power.

 

[fixitflav]

I'm saying it's 0.75bar if head pressure feeding the DHW side, based on the height of the cold tank.

Not sure what you're saying there, but it doesn't matter.

 

[Madrab]

so unless I start looking at a (probably) lower quality, then 30kw it is!

Who told you that?

Most if not all what would be classed as Low, Med or High quality manufacturers make system or HO boilers ranging from 12kw - 37Kw so 30Kw is certainly not the only choice, even if staying with higher end boxes.

I have a 5 bed house @ Glasgow South, out in the sticks - 150 m2 of UFH - and 12 larger rads on a S plus =>7x 600x1200mm K2's, 2x 500x1600 towel rads with a 300L unvented and I run that all on a 24Kw Intergas - which is more than enough. I'm not saying your property doesn't need a 30Kw boiler but it is on the larger side of things.

I think you need a good survey of your property to see exactly what the spaces need as far as heat loss calcs are concerned, couple that with what type of setup would be preferred and go from there

 

[fixitflav]

Does it have to be a system boiler? If the F/E tank, pump etc are OK, could have another heat-only in the new location, depending on the house layout.

 

[JackK]

I have the sae Ideal Mexico 2 boiler

I had a gas engineer suggest I needed a floor standing 42Kw heat only boiler - When I questioned if there was a heat loss calac to support that he looked puzzled - wanted to keep it all open vented

 

[k13wjd]

I should have explained better - Part of the reasoning for the 30kw is that it was the first Worcester Bosch boiler that would allow the flue length I need, which is rediculously long. The smaller models output wise were limited to shorter flue lengths. This house is upside down, boiler is on the ground level of what is a staggered 3 story house, current flue is probably the best part of 10m long.

Now looking at a new boiler location so can use a different model of the same brand, direct to the outside wall. The shower pressure is the only real question here tbh. In reality, the HW tank will need changing, as will, if it's being done as a heat only boiler, the cold tanks in the loft. They are almost certainly coming up on 40 years old. Original boiler, original tank etc. only thing this setup has had changed is a few thermocouples, and 2x 3 way valves/motors over the years.

Thanks for all the help so far, certainly helps to talk things through!!!

 

[Madrab]

This house is upside down, boiler is on the ground level of what is a staggered 3 story house, current flue is probably the best part of 10m long.

Again- there is more than one way to cover that requirement and still stay @ a lower output. A lot of the modern boilers will happily run flue lengths up to or over that requirement E.g. the Intergas Compact SB (18/24/30Kw) - can run it's flue anything up to 15m horizontally or vertically on a 60/100mm std diameter, bends not withstanding.