Accumulator vessel

seannash

Hi,
I'm installing a combi boiler for my heating and hot water system and I'm worried about the water pressure.
I've looked at an accumulator tank but I find it very hard to get a proper grasp on a price. I dont think I need something with a pump. I jsut want to maintain the mains water pressure no matter how many outlets are on (Obviously until the tank runs out)


Has anyone got an accumulator tank or recommend one. Some are quite cheap and other expensive so I cant figure out what the difference is between them.

John.G

seannash wrote: »

Hi,
I'm installing a combi boiler for my heating and hot water system and I'm worried about the water pressure.
I've looked at an accumulator tank but I find it very hard to get a proper grasp on a price. I dont think I need something with a pump. I jsut want to maintain the mains water pressure no matter how many outlets are on (Obviously until the tank runs out)


Has anyone got an accumulator tank or recommend one. Some are quite cheap and other expensive so I cant figure out what the difference is between them.

If you are looking at installing one without a pump then remember that you need a mains pressure 1 to 1.5 bar higher than the minimum required combi cold water pressure.
For example, assuming a min required pressure of 1.5 bar and a mains pressure of 2.5 bar then a 100 litre accumulator will give 28 litres before the pressure falls to 1.5 bar (the air side pre pressure), it will give 37 Litres if the mains pressure is 3 bar so really not a lot, probably only enough for 3 or 4 minutes usage or ~ 6 mins if a 200 litre accumulator is installed. Also bear in mind that several well informed posters on here say that its against regulations to feed a combi boiler directly from the mains, others say that these regs arn't enforced.
You might consider a CW storage tank with a pump which will give far more capacity, remember a 200 litre storage tank will give you 200 litres and in practice a lot more as the mains pressure will be continually filling it even if the pressure is only (or falls to) 1 bar or so.

seannash

John.G wrote: »

If you are looking at installing one without a pump then remember that you need a mains pressure 1 to 1.5 bar higher than the minimum required combi cold water pressure.
For example, assuming a min required pressure of 1.5 bar and a mains pressure of 2.5 bar then a 100 litre accumulator will give 28 litres before the pressure falls to 1.5 bar (the air side pre pressure), it will give 37 Litres if the mains pressure is 3 bar so really not a lot, probably only enough for 3 or 4 minutes usage or ~ 6 mins if a 200 litre accumulator is installed. Also bear in mind that several well informed posters on here say that its against regulations to feed a combi boiler directly from the mains, others say that these regs arn't enforced.
You might consider a CW storage tank with a pump which will give far more capacity, remember a 200 litre storage tank will give you 200 litres and in practice a lot more as the mains pressure will be continually filling it even if the pressure is only (or falls to) 1 bar or so.

Thanks for the reply John.
I gotta admit I'm not well versed in Plumbing and pressure but with a shower on the first floor and a bath and shower on the second floor I think I'll need something (To be officially confirmed by my plumber)


I have read the threads where people debate the regulations but surely an accumulator tank which doesn't have a pump is allowed to feed the combi boiler regardless of location as its just a tank like one you'd have in the attic
Coincidentally I dont have space int he attic for a tank.

John.G

seannash wrote: »

Thanks for the reply John.
I gotta admit I'm not well versed in Plumbing and pressure but with a shower on the first floor and a bath and shower on the second floor I think I'll need something (To be officially confirmed by my plumber)


I have read the threads where people debate the regulations but surely an accumulator tank which doesn't have a pump is allowed to feed the combi boiler regardless of location as its just a tank like one you'd have in the attic
Coincidentally I dont have space int he attic for a tank.

The tank in the attic acts as a "break" tank as the mains water feeds it via a ballcock and is not in direct contact with the water, the accumulator and combi are in direct contact (supply) from the mains.

seannash

John.G wrote: »

The tank in the attic acts as a "break" tank as the mains water feeds it via a ballcock and is not in direct contact with the water, the accumulator and combi are in direct contact (supply) from the mains.

Jaysus it's really splitting hairs isn't it.
Leaving regs aside (I know, I know) I guess I should measure the pressure and flow now and see what I'll get with an accumulator.

K.Flyer

John.G wrote: »

The tank in the attic acts as a "break" tank as the mains water feeds it via a ballcock and is not in direct contact with the water, the accumulator and combi are in direct contact (supply) from the mains.

seannash wrote: »

Jaysus it's really splitting hairs isn't it.
Leaving regs aside (I know, I know) I guess I should measure the pressure and flow now and see what I'll get with an accumulator.

It's not splitting hairs at all.
Two very different installations, both giving very different results. (Apart from the regulations related to mains water connections)
You don't have to install an attic tank.
A cylindrical plastic tank, slightly taller than the average hot water cylinder, with a submersible pump, tucked away in a cupboard will do the job perfectly. And it keeps you within regs.

seannash

K.Flyer wrote: »

It's not splitting hairs at all.
Two very different installations, both giving very different results. (Apart from the regulations related to mains water connections)
You don't have to install an attic tank.
A cylindrical plastic tank, slightly taller than the average hot water cylinder, with a submersible pump, tucked away in a cupboard will do the job perfectly. And it keeps you within regs.

Will that work with a combi boiler.
Also where would it have to be placed. I honestly have no space I side my house (it's tiny) so it's all going to be housed in our pig shed/utility on the ground level

John.G

What is supplying your hot water at the moment?.

seannash

John.G wrote: »

What is supplying your hot water at the moment?.

Absolutely nothing. The place was gutted so it's a completely new system

K.Flyer

seannash wrote: »

Will that work with a combi boiler.

Yes, it would work perfectly.

Also where would it have to be placed. I honestly have no space I side my house (it's tiny) so it's all going to be housed in our pig shed/utility on the ground level

It can go anywhere as long as its protected from frost conditions and your pipe diameters and routes do not impede the flow of water.
Make sure the pump is correctly sized for your requirements and you are sorted. If the budget can afford it, consider getting a pump with a speed controller.
If its going in a shed, then maybe go for a larger tank, so plenty of supply back up.
A job I did has 1,000 litre capacity! so no issues during the water cuts.

Is the gas boiler going in the house or the shed?

seannash

K.Flyer wrote: »

Yes, it would work perfectly.



It can go anywhere as long as its protected from frost conditions and your pipe diameters and routes do not impede the flow of water.
Make sure the pump is correctly sized for your requirements and you are sorted. If the budget can afford it, consider getting a pump with a speed controller.
If its going in a shed, then maybe go for a larger tank, so plenty of supply back up.
A job I did has 1,000 litre capacity! so no issues during the water cuts.

Is the gas boiler going in the house or the shed?

Everything will be in the shed. I still don't see how this is different to an accumulator with a pump. Especially as it will be such a short run.One had a ball cock and the other has compressed air to stop the tank overfilling. Am I right in thinking both are placed before the combi boiler?

John.G

Before deciding on anything, I would install a isolating valve on the end of the mains supply in that shed with a 0 to 6 or 0 to 10 bar pressure gauge Teed in, de isolate the mains and see what the static pressure is, then get a bucket, and measure the flow rate at different pressures by adjusting the isolating valve, try and do this at times of high usage, maybe 0700 hrs or whatever. Make a note of your readings and maybe post back.

seannash

John.G wrote: »

Before deciding on anything, I would install a isolating valve on the end of the mains supply in that shed with a 0 to 6 or 0 to 10 bar pressure gauge Teed in, de isolate the mains and see what the static pressure is, then get a bucket, and measure the flow rate at different pressures by adjusting the isolating valve, try and do this at times of high usage, maybe 0700 hrs or whatever. Make a note of your readings and maybe post back.

Definitely going to do this.
Thanks for the comments so far