Hot and cold water supply pipes under floor, slightly OT

[ian]

We are currently approaching the second fix part of an new extension to the old house. we now need to identify a way to have the hot and cold supply pipes to the washing machine and new boiler run across the kitchen from the rising main and back to the pressurised tank so as not to have exposed pipework round the walls/ up the walls where there are no cabinets planned to hide them. Our kitchen man visited today as we can now confirm the position of the Aga and he can get the measurements to lay out the rest of the room. His suggestion was that we cold run the pipework either alongside a small step in the floor to cross the room, but, as there will be supply pipes and the heating flow and return this would be a lot of pipes to hide under a flooring overhang. He suggested that we then take them around one wall on surface and route them through a "duct" under floor along the door wall to the rising main. This duct would be insulated from the screed and maybe have a metal cover which could be tiled over. Our contractor has stated the " new rules only allow underfloor heating pipes to be underfloor, hot and cold supply pipes need to be surface mounted" We are not planning to lay the pipes directly in the screed being aware of corrosion problems. Anybody heard of this new rule, or is our contractor just blowing smoke to avoid the work involved?

 

[middi]

As long as your hot and cold water pipes are isolated from the screed ( or soil ) to protect them from corrosive salts, and to allow for expansion, you can put as many as you like into the screed and as deep as you want.
Purpose made " pipe wraps" are sold by plumbers merchants.
I'vr never heard that hot and cold pipes should be surface mounted, not as a regulation anyway. I suppose that the only advantage of surface mounted pipes is the relative ease of repair in the unlikely event they should leak.

Middi

 

[Flyfisher]

I've never heard of such a regulation, though I can't claim any particular expertise. We had some kitchen work done in a previous house about 15 years ago and the plumber channelled out the concrete floor to lay CH pipework across the floor to a radiator. He wrapped the pipes in a loose-fitting fibrous covering (the 'pipe-wraps' that Middi mentioned perhaps?) to isoltate them from the concrete and allow for expansion/contraction and then cemented over them. We didn't have any problems.

Perhaps you should ask your builder to refer you to the relevant regulation? I appreciate this will need to be done tactfully!

 

[rogerh]

I've never heard of such a regulation either and can't think it would be practical in most properties. Almost all my heating and water supply pipes are under one floor or other.

 

[88v8]

Our contractor has stated the " new rules only allow underfloor heating pipes to be underfloor, hot and cold supply pipes need to be surface mounted" We are not planning to lay the pipes directly in the screed being aware of corrosion problems. Anybody heard of this new rule, or is our contractor just blowing smoke to avoid the work involved?

If this isn't b****cks, it deserves to be.

Tell him if he doesn't want to put them under the floor, you will do that part of the work yourself.

And if he really can show you there is a rule - the Labour Govt left so many interfering rules after all, why not another one - then put the real pipes under the floor and run dummy pipes on the surface which you can remove after the Govt busybodies have gone.

Ivor

 

[Moo]

Our builders lifted the pamments in our breakfast room, dug trenches for the water supply pipes and some central heating pipes, put back the soil, and relaid the pamments.
So we now have a rather patchy sort of under-floor heating.

But now I've read this thread I'm worrying about that well-buried pipework gradually corroding.........

 

[robgil]

It may be OK in soil Moo, cement on the other hand will corrode copper easily. I've seen copper buried in soil that is older than I am but as Middi says there may be salts in the soil that may speed up the process.

That underfloor rule is a new one on me, I would say it's pants because it doesn't maker any sense. Why shouldn't you bury pipework under cement floor?
The only reason I can see is if the cement isnt deep enough to accommodate the pipework and insulating and still provide the minimum depth coverage ontop without breeching the dpm.

 

[Penners]

I've never heard of such a regulation, though I can't claim any particular expertise.

Add me to that camp. I must say that, as well as running the pipes in some sort of duct to protect them from the concrete, I would also do my utmost to avoid having any buried joints. These always seem to be the most likely source of leaks.

However, if it should transpire that - for whatever reason - running the pipes underfloor is difficult, have you considered taking them up through the ceiling space? I suppose this solution would depend on how easy or otherwise it would to hide them rising up the wall and back down again.

 

[ian]

Thanks folks for your replies and reassurances that I am not in cloud cookoo land. I was sure he was spinning a line, but it was so stupid that I needed reassurance that such a thing had not actually been snuck through. The floor in question is certainly deep enough, 9 inches over a 2 coat liquid dpc, incorperating 100mm of celotex and 2 further plastic sheet DCPs. Sorry Penners, the roof space is out, the room is a single story vaulted area open plan onto the two storey kitchen/ bathroom and the whole point is to take the pipework to the external boiler and back to the bathroom/ water tank and rest of house heating without touching the walls and ceiling space. I will, tactfully of course, request complience with our desires.

 

[robgil]

If it is a long run under concrete use an expansion loop. :wink:

 

[middi]

The most vulnerable points, when hot water pipes are encased in solid floors, is when the pipes turn through 90 deg.
At this point the pipes need a good expansion clearance due to the long pipe run prior to the bend. ( all plumbers will/should know that)

Middi

 

[robgil]

An expansion loop will do that for you Middi, not so critical on shorter runs as there will be room for expansion in the insulating.

There are various different types and sometimes flexible pipe can be used.

 

[tony]

Your heating man is indeed correct, you cannot run potable water in a position where it will warm up.

Its the water supply regs you want to look at.

 

[tobydog]

Due logistics, our hot and cold water pipes to the sink in the new kitchen extension run under the floor. We have underfloor heating and in the winter the cold water sitting in the pipe warms up to the extent that we use this water for hand washing rather than running the hot tap and triggering the boiler. Saves on oil but it's a pain if you actually want cold water because the pipe run under the heated floor is about 20ft in total. Is this really a health hazard if the tap is used regularly?

 

[Flyfisher]

It sounds like there are two issues here; burying pipes in a concrete floor and keeping potable water supplies cold.

Ian's original post didn't mention underfloor heating so I can't see that burying the pipes will cause any heating to the water within (well, no more than surface mounted pipes in a centrally heated house anyway).

I hadn't heard Tony's point about not installing potable water pipes where they could become heated, but I can understand the rationale for this and would agree that installing such pipes in a heated concrete floor might not be a good idea - legionella being the main risk I presume?

Perhaps Ian could give us an update about how things progressed?

Regarding Tobydog's question, I've heard that in 'green' water heating systems where the water is not always guaranteed to reach a sufficient temperature to kill legionella, it is necessary to arrange for the hot water tank to be raised to a 'properly hot' temperature at least once a week to ensure there is no dangerous build up of legionella (easily achieved with a timer and immersion heater).

If these guidelines allow a week of warmish water to stand, then this suggests, to me, that regular flushing of warm water in a short length of pipe is probably safe enough (though the usual caveats about amateur ramblings apply!).

Legionella behaviour at various temperatures can be found at: http://en.wikipedia.org/wiki/Legionella

 

[AMc]

Regarding Tobydog's question, I've heard that in 'green' water heating systems where the water is not always guaranteed to reach a sufficient temperature to kill legionella, it is necessary to arrange for the hot water tank to be raised to a 'properly hot' temperature at least once a week to ensure there is no dangerous build up of legionella (easily achieved with a timer and immersion heater).

If these guidelines allow a week of warmish water to stand, then this suggests, to me, that regular flushing of warm water in a short length of pipe is probably safe enough (though the usual caveats about amateur ramblings apply!).

I have an air source heat pump providing 300ltr of hot water at 45C. My tank is raised to 65C overnight once a week by the heat pump which is still more efficient than the immersion. It then stays near that point pasteurising away until the first shower the following morning.
The point is the hot water tank is raised to 65C killing the germs in the tank as well as the water that happens to be in it at the time. We use more than one whole tank a week and it is continuously refilled. The hot water in the pipes cools fast enough to avoid providing a breeding ground and of course you aren't supposed to drink water out of the hot supply.

If you have a run of drinking water pipe heated to a nice bacteria friendly 35-40C by underfloor heating for long periods of time you won't raise the temperature of that pipe to 65C to kill the germs - particularly in the cold feed. Each run of a couple of litres at the tap will simply add fresh water into the germ soup created in there - yuk. I can see why that wouldn't be a good idea.

Our cold and hot water pipes were placed over the "over site" slab and under the board insulation with the underfloor heating fixed to that and the concrete screed over that so the are isolated from the heated screed.

 

[Penners]

potable water supplies

Isn't all water potable?

All you need is a bucket.

 

[tobydog]

Given that our cold water feed under the heated floor to the kitchen sink is a direct feed from the mains, is there in fact a very low risk of bacteria actually being present in the pipe? Clearly Legionnaires Disease can only manifest itself if the bacteria is present in the mains water source in the first place. Just thinking logically for peace of mind!

 

[AMc]

Good question - the OP Ian was feeding a boiler and a washing machine so the risk IMHO would be quite small but a kitchen tap is a bit more worrying.

My understanding is that legionella is pretty much everywhere in low concentrations in fresh water which Wikipedia backs up but it isn't always gospel. To multiply to dangerous concentrations it needs warmth 20-50C.

If legionella weren't present in mains water then you would only need to heat a pressurised water system to 65C once to rid it of any risk forever. The mains water coming into the tank is a closed system after its connected so there would be no way for it to get in? As the pasteurisation of the tank is done weekly on a manufacturers hard coded preset I have to assume its necessary to repeatedly disinfect as there is a risk that water coming in will be/could be carrying bacteria.

My guess would be that the amount of water available and the frequency with which it is flushed through your kitchen pipe is helpful and as Wiki says "Some people can be infected with the Legionella bacteria and have only mild symptoms or no illness at all.".

It sounds like your pipes shouldn't have been laid in this way but what you do about it now I'm not honestly sure - my guess is it isn't a particularly high risk but I'm no expert at all. Anyone else got any thoughts?

 

[Penners]

I'm no expert either, but I've lost count of the number of houses I've known in which the hot water pipe runs closely in parallel with the cold, so that the cold tap runs hot for some time. The occupants of such houses seem to have survived this arrangement without succumbing to legionella.