Condensate from sealed cold water tank in attic

CorBur · 11-01-2015 10:33pm #1

Hi all.
We had our heating upgraded in the summer of 2013.
I opted for a gas combi boiler. Due to insufficient mains pressure we had a water tank with integrated submersible pump installed in the attic which provides the necessary pressure for the boiler to operate.
We have now noticed a stain in the ceiling which the tank is mounted above. We are not sure how long this has been developing as we don't use the room.
After investigation, i believe the stain is being caused by condensation which is forming on the outside of the tank and running down to the platform on which the tank is mounted. This has now penetrated the attic insulation and seeping through the plasterboard.

i am going to ring the plumber that did the installation to call him back as i feel he is responsible and should correct the issue.
My question is, how should this be done? Would a bund under the tank be an option? Or if an insulated enclosure was installed around the tank, would this take care of the condensation?

Thanks in advance for any advice.

nmacc · 11-01-2015 11:05pm

For condensation to form on the outside of the tank there would need to be a significant temperature differential between the air in the loft and the water in the tank. The incoming mains will definitely be cold enough for condensation to form on the tank, but usually it's hanging around in the tank for long enough to heat up to the point that condensation isn't a problem.

I have only seen this happen with tanks that are mounted high up in the loft. When the tank is directly on the rafters the heat rising under the tank usually warms it up enough. Loft tanks should always be insulated and there should never be insulation under a tank so that heat will rise from the house and stop it freezing. If it's raised up then a box made up of polystyrene sheets should conduct warmth to the tank while not cooling the room below appreciably.

Check the fitting of the tank lid first. Condensation will definitely form on the underside of the tank lid. Depending on how this is fitted, the condensate might run down the outside of the tank instead of the inside.

If the lid is correct I wouldn't be too quick to blame your plumber. It's hardly his fault that the air in the loft is warm and the water in the mains is cold.

Sleeper12 · 12-01-2015 12:09am

I totally agree with nmacc. It seems very unfair to blame the plumber.

Andrew_Doran · 12-01-2015 12:09pm

You have warm moist air leaking from the inside of the house though holes in the ceiling or tops of stud walls, or attic hatch, or extractor fans, or up wall cavities, or all of the above, whatever. Warm air always rises. It's then condensing on the coldest thing in the attic which is the water tank. It's not the plumber's fault.

RJF · 12-01-2015 12:58pm

Did you actually see the condensation formed on the side of the tank? Was there a little or a lot? A small amount MAY evaporate naturally and not be causing the stain. The sides of the tank should be insulated anyway but often are not with no problems. Do not insulate under the tank. The tank connections should be checked for slow leaks. Wipe them dry and watch them for 15/20 minutes and see if anything develops. Requires a bit of patience but a good time to practice the old Zen meditation. Even a couple of drops getting through the tank connection will stain over time. Also any fittings on the pipes in the area should be checked for slow leaks also. If it is condensation on the SIDES of the tank, insulation should solve it.

RJF · 12-01-2015 1:06pm

A further thought. From your description it sounds like your tank might be on a platform with insulation under it. You would need to remove this and insulate the sides and top of the tank. This should solve you problem assuming no leaks.

Calahonda52 · 12-01-2015 2:34pm

1: just to get the terminology right
I believe its Condensation, as opposed to Condensate, from sealed cold water tank in attic.
2: What do you mean by sealed cold water tank.
Is the tank insulated and if so exactly how with what.
3: Is the attic floor under the tank insulated and with what?

As noted above, you must have a lot of very warm air getting into the attic space to create this problem?

Is there any condensation on the underside of roof felt.

I don't know about the heat from the room below drying off the condensation:
a quick look at the math suggests not:
Specific heat of water is 4.2kJ/kg/ degree

Cold water coming in is probably 10 degrees and the dew point with warm air could be 16

so 6 degrees C for maybe 60 kg of water is 1512 kJ or 1512000 joules

A Watt is a Joule/second so say the water is changed very 12 hours
And Power is W/t

So power required for this is 1512000/(12*60*60) = 42 Watts

This then has to be adjusted for the thermal conductivity of the plastic so my guess, as suggested earlier its a slow leak

Any insulation around the tank needs to be airtight, otherwise the mouse air will bet through it due to the differential vapour pressures.

RJF · 12-01-2015 3:26pm

Hi Calahonda52. Like your calculations, but check the math (35 watts?). Also that would seem to be in very controlled conditions. An attic will experience variable conditions due to air tightness, ventilation, use of space, compactness of insulation etc. Some condensation is not unusual on tanks and fittings and does not always cause a problem. However it is best avoided. The idea of the heat from the room below is the raise the heat of the water in the tank to minimize condensation.

CorBur · 13-01-2015 9:11pm

Thanks for all the replies.

nmacc wrote: »

For condensation to form on the outside of the tank there would need to be a significant temperature differential between the air in the loft and the water in the tank. The incoming mains will definitely be cold enough for condensation to form on the tank, but usually it's hanging around in the tank for long enough to heat up to the point that condensation isn't a problem.

I have only seen this happen with tanks that are mounted high up in the loft. When the tank is directly on the rafters the heat rising under the tank usually warms it up enough. Loft tanks should always be insulated and there should never be insulation under a tank so that heat will rise from the house and stop it freezing. If it's raised up then a box made up of polystyrene sheets should conduct warmth to the tank while not cooling the room below appreciably.

Check the fitting of the tank lid first. Condensation will definitely form on the underside of the tank lid. Depending on how this is fitted, the condensate might run down the outside of the tank instead of the inside.

If the lid is correct I wouldn't be too quick to blame your plumber. It's hardly his fault that the air in the loft is warm and the water in the mains is cold.

The tank is a cylindrical plastic tank (200lt) approx 5ft in height with a submersible pump fitted (aqua box?) The lid is only about 200mm in diameter.
The reason I am annoyed with the plumber is that he was given the complete job of totally upgrading our heating and bathroom. He acted as a main contractor and brought in a carpenter and other trades to provide a complete overhaul. I had insulated the attic previous to all this work being carried out. The tank changed location in the attic due to the size of it. I have checked and he did not remove the insulation under the tank or insulate the tank itself. I now have to have a ceiling repainted due to his negligence.

Andrew_Doran wrote: »

You have warm moist air leaking from the inside of the house though holes in the ceiling or tops of stud walls, or attic hatch, or extractor fans, or up wall cavities, or all of the above, whatever. Warm air always rises. It's then condensing on the coldest thing in the attic which is the water tank. It's not the plumber's fault.

As above. I believe his negligence has led to this.

RJF wrote: »

Did you actually see the condensation formed on the side of the tank? Was there a little or a lot? A small amount MAY evaporate naturally and not be causing the stain. The sides of the tank should be insulated anyway but often are not with no problems. Do not insulate under the tank. The tank connections should be checked for slow leaks. Wipe them dry and watch them for 15/20 minutes and see if anything develops. Requires a bit of patience but a good time to practice the old Zen meditation. Even a couple of drops getting through the tank connection will stain over time. Also any fittings on the pipes in the area should be checked for slow leaks also. If it is condensation on the SIDES of the tank, insulation should solve it.

Yes i noticed the condensation on the outside of the tank. I can also see where the condensation has run down the tank onto the plywood platform and from there into the insulation and through to plasterboard. I have investigated the pipes and fittings. All are dry.

RJF wrote: »

A further thought. From your description it sounds like your tank might be on a platform with insulation under it. You would need to remove this and insulate the sides and top of the tank. This should solve you problem assuming no leaks.

Thanks.

Calahonda52 wrote: »

1: just to get the terminology right
I believe its Condensation, as opposed to Condensate, from sealed cold water tank in attic.
2: What do you mean by sealed cold water tank.
Is the tank insulated and if so exactly how with what.
3: Is the attic floor under the tank insulated and with what?

As noted above, you must have a lot of very warm air getting into the attic space to create this problem?

Is there any condensation on the underside of roof felt.

I don't know about the heat from the room below drying off the condensation:
a quick look at the math suggests not:
Specific heat of water is 4.2kJ/kg/ degree

Cold water coming in is probably 10 degrees and the dew point with warm air could be 16

so 6 degrees C for maybe 60 kg of water is 1512 kJ or 1512000 joules

A Watt is a Joule/second so say the water is changed very 12 hours
And Power is W/t

So power required for this is 1512000/(12*60*60) = 42 Watts

This then has to be adjusted for the thermal conductivity of the plastic so my guess, as suggested earlier its a slow leak

Any insulation around the tank needs to be airtight, otherwise the mouse air will bet through it due to the differential vapour pressures.

Condensate is the liquid caused by condensation. This liquid is my issue.
The tank is a plastic cylinder which a small lid threads into on top. It also has an integrated submersible pump. Aqua box is the brand.
Yes the floor is insulated. I can see from all of the replies that this should have been removed.
Felt is dry.
Thanks for running the calculation.

Calahonda52 · 13-01-2015 9:29pm

Condensate is the liquid caused by condensation. This liquid is my issue.

[100% agree.
My reasoning was as follows
In a plumbing forum such as this, condensate general refers to the liquid that comes from condensing boilers, it is mildly acidic and needs to be dealt with properly.
In the oil and gas industry, condensate has a specific meaning as well.
I should have been more specific

Mea Cupla ]

The tank is a plastic cylinder which a small lid threads into on top. It also has an integrated submersible pump. Aqua box is the brand.
Yes the floor is insulated.

I can see from all of the replies that this should have been removed.
[ I disagree 100% with this assertion and I would strongly advise you not building a legal case around this point unless you can find it in some building regulations.
The tank should have been insulated with airtight insulation to stop warm air getting near the surface through stuff like glass fibre wrap.

Before you go much further be 100% certain there is no leak]

Felt is dry.
Thanks for running the calculation.

Shrap · 14-01-2015 1:05pm

This might sound a bit stupid to the plumbers here because I have no idea what a gas combi heating system is, or about this tank with submersible pump, but I can tell you that when I upgraded my solid fuel range a few years ago, it exposed so many problems with the existing plumbing/rads that I had to replace the entire system

Basically, the range was causing "pitching" and the header tank was acting like a radiator due to the positioning of the pump from the immersion cylinder and the badly done pipe work that was there originally.

So that's why I'm just wondering are you sure there's no hot water pitching back into your tank? Clouds of steam guaranteed - in my case it waterlogged the insulation before I knew it and the whole attic had to be redone too. Hope you sort it. Very depressing.

Ps. I also blamed my plumber at first but it turned out to be the original plumber who did everything arsewise. Be careful before you accuse!

nmacc · 14-01-2015 1:56pm

...."This might sound a bit stupid to the plumbers here..."

Not at all; pitching is a very common cause of moisture in the loft.
It can be quite dramatic. I was called once to a house where the system had been pitching for a very long time before enough water penetrated the insulation to mark the ceiling. When I went up into the loft I found that the entire roof - felt, rafters, etc. - was covered in thick white fungus/mould which had grown in the condensation resulting from the warm, moist air coming from the uncovered tank into which the hot water was pitching. It was quite scary really, a bit like climbing into the belly of some enormous beast - shades of Alien!

Pitching following the changing of a boiler is quite common. Traditionally the circulation pump was fitted in the return line, but modern condensing boilers have the pump in the flow line (I know I looked into why this is the case, but I can't remember why, must be old age). Anyway, with an open system this can cause the hot water to travel up the central heating expansion pipe and pitch into the tank. Solution is to add an expansion vessel and seal the system.

This case though is quite unusual. I've been thinking about it and while I have seen condensation on the outside of a CWS storage tank being bad enough to stain the supporting platform and timber, I don't remember ever seeing it bad enough to stain the ceiling below without additional complicating factors.

I've seen the rectangular blue tanks with the inspection lids as described, but I've never seen one 1500 high in a loft. It could be similar to this, but if so, I hope there's a lot of timber to support it as 225kg is quite a point load. Possibly the large vertical surface is concentrating the amount of condensation dripping down.

Calahondra has done an excellent job with the maths, but I think it might oversimplify things a bit, as it assumes a full tank of water at the temperature of the rising main, whereas in most cases the water will be sitting in the tank for quite some time, allowing it to acclimatise. Perhaps the OP has a large bath and frequently drains the tank completely?

I would think removing the insulation under the tank and wrapping it in rockwool, with a layer on top would solve the problem.

Shrap · 14-01-2015 2:11pm

nmacc wrote: »

...."This might sound a bit stupid to the plumbers here..."

Not at all; pitching is a very common cause of moisture in the loft.
It can be quite dramatic. I was called once to a house where the system had been pitching for a very long time before enough water penetrated the insulation to mark the ceiling. When I went up into the loft I found that the entire roof - felt, rafters, etc. - was covered in thick white fungus/mould which had grown in the condensation resulting from the warm, moist air coming from the uncovered tank into which the hot water was pitching. It was quite scary really, a bit like climbing into the belly of some enormous beast - shades of Alien!

Cheers! Yes, exactly that, sadly

Had to replace all insulation and spray the timbers with a mould killer. God, it was an awful job.

Sleeper12 · 14-01-2015 10:46pm

Still can't see how the plumber gets blamed. I would suspect that the person who insulated the attic itself should carry most of the blame. There obviously isn't enough air circulating in the attic. It sounds like the installation was shoved into the eaves instead of leaving the required gap.
Might be an idea to remove some insulation to let the attic breath.

dathi · 15-01-2015 11:03am

Calahonda52 wrote: »

Condensate is the liquid caused by condensation. This liquid is my issue.

]

I can see from all of the replies that this should have been removed.
[ I disagree 100% with this assertion and I would strongly advise you not building a legal case around this point unless you can find it in some building regulations.

n.

http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,27357,en.pdf page six

CorBur · 17-01-2015 11:22pm

Sleeper12 wrote: »

Still can't see how the plumber gets blamed. I would suspect that the person who insulated the attic itself should carry most of the blame. There obviously isn't enough air circulating in the attic. It sounds like the installation was shoved into the eaves instead of leaving the required gap.
Might be an idea to remove some insulation to let the attic breath.

Insulated attic myself. Plenty of air circulating. Tank was moved to an area in the middle of attic due to height limitations of area where old tank was installed.Insulation was not removed from under the platform on which the tank was installed.

dathi wrote: »

@ Dathi

My installation looks nothing like that.... Thanks for the info.

Plumber has called and has admitted that he should have done more. He has agreed to sort out the insulating of the tank and the repair of the ceiling below once we have ensured that no further water is gathering.

Thanks to all for opinions.

jakko86 · 18-01-2015 10:51am

Sleeper12 wrote: »

Still can't see how the plumber gets blamed. I would suspect that the person who insulated the attic itself should carry most of the blame. There obviously isn't enough air circulating in the attic. It sounds like the installation was shoved into the eaves instead of leaving the required gap.
Might be an idea to remove some insulation to let the attic breath.

Would agree with this I've seen it a few times where the tank gets condensation due to poor ventilation in the attic. There might be some ventilation but maybe not enough cross flow of air to have proper ventilation.

Sleeper12 · 18-01-2015 12:02pm

jakko86 wrote: »

Would agree with this I've seen it a few times where the tank gets condensation due to poor ventilation in the attic. There might be some ventilation but maybe not enough cross flow of air to have proper ventilation.

It's not possible to have condensation on the level described by OP if attic has enough ventilation.
At the end of the day the plumber is happy enough to do it, so happy days.

Condensate from sealed cold water tank in attic

Comments