Author Topic: Question about hot water expansion vessels size  (Read 475 times)

Gattopardo

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Question about hot water expansion vessels size
« on: 30 October, 2021, 07:50:39 pm »
Will replacing a 5l expansion vessel with a 12l be a bad idea?

Re: Question about hot water expansion vessels size
« Reply #1 on: 30 October, 2021, 09:49:36 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.
Quote from: Kim
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Gattopardo

  • Lord of the sith
  • Overseaing the building of the death star
Re: Question about hot water expansion vessels size
« Reply #2 on: 30 October, 2021, 10:03:41 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.

Note this is for the hot water, not the central heating, I think. This is not a combi boiler but a boiler with a water tank. Spent half a day trying to figure out the plumbing pipe work and gave up as the pipes disappear under floors and in ceilings.

Re: Question about hot water expansion vessels size
« Reply #3 on: 30 October, 2021, 11:21:35 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.

Note this is for the hot water, not the central heating, I think. This is not a combi boiler but a boiler with a water tank. Spent half a day trying to figure out the plumbing pipe work and gave up as the pipes disappear under floors and in ceilings.
It really doesn't make any difference what the expansion vessel is connected to. It's there to keep the pressure reasonably constant as the water heats up and cools down, so a larger one will cause less pressure change. The only reasons not to go for a larger one is cost and space, along with the fact that some pressure change is acceptable, so if you know that 5 litres is adequate, 12 litre is just more money and a bigger thing to hide. However, if 5 litres is marginal and could lead the pressure changing too much, or you have a 12 litre expansion vessel available, you might as well use it.

As both need similar fixing arrangements, and either can be fitted by one person, there's little to chose between them. If you had a 1 litre or smaller vessel, it might be possible to mount it on a pipe, saving the cost of mounting on brackets etc. If you had a 100 litre tank, it would need serious mounting hardware, but neither of those extremes apply here.

Quote from: Kim
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Gattopardo

  • Lord of the sith
  • Overseaing the building of the death star
Re: Question about hot water expansion vessels size
« Reply #4 on: 31 October, 2021, 03:44:53 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.

Note this is for the hot water, not the central heating, I think. This is not a combi boiler but a boiler with a water tank. Spent half a day trying to figure out the plumbing pipe work and gave up as the pipes disappear under floors and in ceilings.
It really doesn't make any difference what the expansion vessel is connected to. It's there to keep the pressure reasonably constant as the water heats up and cools down, so a larger one will cause less pressure change. The only reasons not to go for a larger one is cost and space, along with the fact that some pressure change is acceptable, so if you know that 5 litres is adequate, 12 litre is just more money and a bigger thing to hide. However, if 5 litres is marginal and could lead the pressure changing too much, or you have a 12 litre expansion vessel available, you might as well use it.

As both need similar fixing arrangements, and either can be fitted by one person, there's little to chose between them. If you had a 1 litre or smaller vessel, it might be possible to mount it on a pipe, saving the cost of mounting on brackets etc. If you had a 100 litre tank, it would need serious mounting hardware, but neither of those extremes apply here.

Hello

The hot water tank is 63l, the 12l is the smallest I can find at a diy store.  Looks like the ones on the shelf were made in 2018.  Should that long on the shelf matter?

Re: Question about hot water expansion vessels size
« Reply #5 on: 31 October, 2021, 10:48:45 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.

Note this is for the hot water, not the central heating, I think. This is not a combi boiler but a boiler with a water tank. Spent half a day trying to figure out the plumbing pipe work and gave up as the pipes disappear under floors and in ceilings.
It really doesn't make any difference what the expansion vessel is connected to. It's there to keep the pressure reasonably constant as the water heats up and cools down, so a larger one will cause less pressure change. The only reasons not to go for a larger one is cost and space, along with the fact that some pressure change is acceptable, so if you know that 5 litres is adequate, 12 litre is just more money and a bigger thing to hide. However, if 5 litres is marginal and could lead the pressure changing too much, or you have a 12 litre expansion vessel available, you might as well use it.

As both need similar fixing arrangements, and either can be fitted by one person, there's little to chose between them. If you had a 1 litre or smaller vessel, it might be possible to mount it on a pipe, saving the cost of mounting on brackets etc. If you had a 100 litre tank, it would need serious mounting hardware, but neither of those extremes apply here.

Hello

The hot water tank is 63l, the 12l is the smallest I can find at a diy store.  Looks like the ones on the shelf were made in 2018.  Should that long on the shelf matter?
I would expect an expansion vessel to last 25 years, so I wouldn't worry about a few years on the shelf.

I had a quick look and the price difference between 5 litres and 12 litres is minimal. Also you should allow for 4.5 % expansion, so that is 2.8 litres that the expansion vessel needs to absorb. I don't know how expansion vessel sizes are measured, but if the overall volume is 5 litres, 2.8 litres of change is too much. This link https://www.unventedcomponentseurope.com/help-and-information/potable-expansion-vessel-sizing-guide/ says you should have at least 8 litres for a 63 litre tank.
Quote from: Kim
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Re: Question about hot water expansion vessels size
« Reply #6 on: 31 October, 2021, 10:57:55 pm »
This calculator https://mikrofill.com/vessel-calculator has the expansion vessel size as a minimum. If the pressure rise has to be smaller, the expansion vessel ends up larger.
Quote from: Kim
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Gattopardo

  • Lord of the sith
  • Overseaing the building of the death star
Re: Question about hot water expansion vessels size
« Reply #7 on: 01 November, 2021, 01:01:55 pm »
No, the bigger the better. A larger expansion vessel will reduce how much the pressure changes as expansion happens.

Note this is for the hot water, not the central heating, I think. This is not a combi boiler but a boiler with a water tank. Spent half a day trying to figure out the plumbing pipe work and gave up as the pipes disappear under floors and in ceilings.
It really doesn't make any difference what the expansion vessel is connected to. It's there to keep the pressure reasonably constant as the water heats up and cools down, so a larger one will cause less pressure change. The only reasons not to go for a larger one is cost and space, along with the fact that some pressure change is acceptable, so if you know that 5 litres is adequate, 12 litre is just more money and a bigger thing to hide. However, if 5 litres is marginal and could lead the pressure changing too much, or you have a 12 litre expansion vessel available, you might as well use it.

As both need similar fixing arrangements, and either can be fitted by one person, there's little to chose between them. If you had a 1 litre or smaller vessel, it might be possible to mount it on a pipe, saving the cost of mounting on brackets etc. If you had a 100 litre tank, it would need serious mounting hardware, but neither of those extremes apply here.

Hello

The hot water tank is 63l, the 12l is the smallest I can find at a diy store.  Looks like the ones on the shelf were made in 2018.  Should that long on the shelf matter?
I would expect an expansion vessel to last 25 years, so I wouldn't worry about a few years on the shelf.

I had a quick look and the price difference between 5 litres and 12 litres is minimal. Also you should allow for 4.5 % expansion, so that is 2.8 litres that the expansion vessel needs to absorb. I don't know how expansion vessel sizes are measured, but if the overall volume is 5 litres, 2.8 litres of change is too much. This link https://www.unventedcomponentseurope.com/help-and-information/potable-expansion-vessel-sizing-guide/ says you should have at least 8 litres for a 63 litre tank.

Ah so the expansion tank is too small hence why it hasn't lasted long.

The paperwork with this https://www.castorama.fr/groupe-de-securite-anti-calcaire-nf-20x27-pour-chauffe-eau-alimentation-verticale-diall/3454975220548_CAFR.prd (i'll get aphoto too) says that below 70l 5l expansion vessel is correct.  But has no calculation.

Looks like the only expansion vessel I can get today is https://www.castorama.fr/vase-d-expansion-sanitaire-12-l/3540731600119_CAFR.prd and the feed back isn't good.  Same on all the other chains DIY stores.