10mm, 15mm and 22mm Pipe Use

[Barney12]

So, I'm just planning my first fix pipe runs. Am I on the right lines?

 

Im intending to use a manifold system as others have here as the ability to isolate is so useful. 

 

We have a about 3-4bar and 17 ish litres a minute flow.

The furthest point is the kitchen which I estimate will be a 20-25m run of pipe. 

The bathrooms are both only circa 10-15m runs.

 

All basin taps (hot and cold) - 10mm

Toilets - 10mm

Kitchen taps, utility taps, dishwasher, washing machine (hot and cold) - 15mm

Showers (hot and cold) - 15mm

Bath (hot and cold) - 22mm

Flow and Return for UFH Manifold- 22mm

 

Ta in advance! 

[Nickfromwales]

22 to the bath is pointless TBH, as most modern taps are 1/4 turn with small bore innards. . I'd use 15mm, as with 3-4 bar / 17lpm flow available you'll not really notice any reduction in resistance going to the bigger pipe size. 22 is only really for huge baths with full bore fillers, pumped baths or for gravity fed hot water supplies. ?

[Onoff]

+1. I ditched 22mm copper and went with a mix of 15mm copper and PB to the bath in @Nickfromwales advice. Works perfectly.

 

I can assure you it empties both the CWS tank and hot cylinder very quickly. One day I'll be able to fill this huge bath!

 

Btw mine is all gravity fed.

[Barney12]

41 minutes ago, Nickfromwales said:

22 to the bath is pointless TBH, as most modern taps are 1/4 turn with small bore innards. . I'd use 15mm, as with 3-4 bar / 17lpm flow available you'll not really notice any reduction in resistance going to the bigger pipe size. 22 is only really for huge baths with full bore fillers, pumped baths or for gravity fed hot water supplies. ?

 

OK, ta.

I'm still trying to get comfortable with 10mm, it just feels wrong. Call me old fashioned

[ProDave]

25 metre run to the kitchen worries me.

 

Old house, the kitchen was a long way from the tank, and part of the run in 22mm. Result it took an age for the hot water to arrive. I was constantly being told off for rinsing stuff in cold water, and my reply was I didn't want the time, or wasted hot water, just to purge the long run of pipe to get the tiny bit of hot I needed.

 

I would seriously see if you can shorten that. Otherwise, seriously, I would buy a length of 10mm pipe and try it to see if it gives enough flow at a kitchen tap over that distance.

 

Our new house I have changed the layout a bit specifically to get the HW tank closer to the kitchen, where is is (or should be!) used most often.

 

I recall this argument with my father who was an old school plumber. When he plumbed my first house, he insisted on a long run of 22mm to the bath, and the basin fed from that. I argued for a separate 10 or 15mm for the basin, but he just could not see the smaller volume of water in the pipe would make it quicker to deliver hot water.

 

 

[jack]

We have this problem with our kitchen. It's the one long run in the house, and it takes (guesstimate) 15-20 seconds to run hot.  Drives me mental, because you can't do a quick warm hand wash or hot wash of dishes.

 

First world problems, I know, but if I were doing this again I'd consider a local instantaneous heater at this point. The alternative is a pumped loop, but I didn't want to get into all that extra plumbing, equipment and energy loss, especially in a well-insulated house.

[Onoff]

Ooh...15 - 20 seconds! Luxury!

 

When you want a shower do you have to put the handset in the floor to get it going then if that doesn't work take it off? Then if that fails unscrew the hose from the bar valve and hold you thumb on and off the outlet? Then there's the guessing game whether when it eventually stops being freezing cold it'll be lukewarm or actually a decent (rarely too hot) shower!

 

Happens to a "mate" of mine... 

 

 

[jack]

I did say "first world problems".  Would it help if I added a hashtag? 

 

 

I just timed it - 25 seconds to full heat.  

 

As for your shower scenario, I lived with exactly that situation for over two years in the bungalow we demolished to build the new house (and the rental we had for a year during the build wasn't much better).  The water pressure was so low that we gave up trying to shower and instead spent 10 mins dripping enough water into the bath every day to have a wash.  Reused the bath water too, because there are only 24 hours in the day, which is more than it would have taken to run 4 x 3" deep baths. 

 

Oh, and I didn't mention the 45 second wait for hot water at the sink in the main bathroom of the new house.  Weirdly, it's the only tap upstairs that has any problem - the shower in the same room runs hot in 5 seconds.  It's actually one of the closest taps to the DHW tank as well.  I can only assume it's taken via some circuitous route for some unknown reason.

 

And finally, my answer wasn't to whine about hardship.  Someone asked about plumbing and specifically mentioned long runs. 20 seconds IS a long time to stand there with the tap running before you can do a quick hand wash in warm water.  I'd be more accepting of it if the house were old and that's how the plumbing worked, but we spent a lot of time, money and energy building a new house, and this is one of the (yes, minor) things that irks me about the result.  If I hadn't yet done this and were about to make a decision about plumbing, I'd be interested in hearing what others would have done differently.

[Nickfromwales]

38 minutes ago, jack said:

We have this problem with our kitchen. It's the one long run in the house, and it takes (guesstimate) 15-20 seconds to run hot.  Drives me mental, because you can't do a quick warm hand wash or hot wash of dishes.

 

First world problems, I know, but if I were doing this again I'd consider a local instantaneous heater at this point. The alternative is a pumped loop, but I didn't want to get into all that extra plumbing, equipment and energy loss, especially in a well-insulated house.

I wouldn't begrudge a hot return loop in a passive performing home TBH, as with loads of additional pipe insulation, and the  remaining losses usually plenty offset by pv generation, it seems a no brainer. That is typically only where you have an UVC or a TS eg some form of stored DHW ( as most instant water heaters don't provision for hot return integration ). 

With all the savings and efficiencies gained from having a 'cheap to run' home I would give myself a few such 'perks' if it were me.  

 

[jack]

That info would have been useful about 18 months ago!  

 

It just seemed like a lot of complication and cost for a small return at the time we were planning it.  With hindsight, perhaps we should have plumbed return loops, especially to the kitchen, but it isn't really that big a deal.  If I really need hot water in a hurry I can use the boiling water tap and add some cold water if I need to drop the temp (not recommended as an approach for handwashing!)

 

[Bitpipe]

We specced a hot return (it's in 15mm vs the main hot circuit of 22mm).

 

Instead of using a pipe stat and timer, which was the plumber's default option, the sparky wired it into the same circuit as the MVHR boost which is activated when the bathroom light comes on or by a PIR in each bathroom - runs for a good 10 mins after each has been deactivated.

 

We don't have any sensor in the kitchen, however there is a MVHR boost close to hand so I just hit that and presto - hot water

[Barney12]

9 hours ago, ProDave said:

25 metre run to the kitchen worries me.

 

Old house, the kitchen was a long way from the tank, and part of the run in 22mm. Result it took an age for the hot water to arrive. I was constantly being told off for rinsing stuff in cold water, and my reply was I didn't want the time, or wasted hot water, just to purge the long run of pipe to get the tiny bit of hot I needed.

 

I would seriously see if you can shorten that. Otherwise, seriously, I would buy a length of 10mm pipe and try it to see if it gives enough flow at a kitchen tap over that distance.

 

Our new house I have changed the layout a bit specifically to get the HW tank closer to the kitchen, where is is (or should be!) used most often.

 

I recall this argument with my father who was an old school plumber. When he plumbed my first house, he insisted on a long run of 22mm to the bath, and the basin fed from that. I argued for a separate 10 or 15mm for the basin, but he just could not see the smaller volume of water in the pipe would make it quicker to deliver hot water.

 

 

 

I'm from the same school as your Dad. Big pipe = faster delivery. More pipe = more water, this must be faster.

Something tells me I'm wrong due to Physics or summin'  

[jack]

22mm pipe has around 380mm² cross sectional area, compared to 80mm² for 10mm pipe.  Ignoring friction, you therefore need nearly 5 times the flow rate to achieve the same water speed in 22mm compared to 10mm.  

 

The flow rate is set by the tap.  Since the tap doesn't have a cross sectional area equivalent to anything like 22mm pipe even when it's on full, water will necessarily move slower in the 22mm than the 10mm for a given (relatively low) flow rate.

 

[TerryE]

Have a look at my post:

Where I discuss some of these issue and give a couple of good references.  We have a HEP2O + central manifold system.  The largest copper run is less than 2m so I ended up doing all of mine in 22mm as the TMV, water softener, etc. dominated both the pressure drop on the acoustic output.  All of our radials are in 15mm so keep it simpler an minimise costs (our runs are fairly short, so the pipe cost savings in going down to 10mm for some run is less than the cost of the extra 15/10 reduction couplers).  There was an argument fo using 10mm on all of our low flow hot taps, but quite honestly when I look at the usage and costs of dead water heat loss, it just wasn't worth the hassle.  

[Mikey_1980]

Our plumber specced a hot return in our house as it is a mixture of bungalow and 2 storeys the pipe runs are long, and I am really glad he did. We have it on a 7 day timer so weekdays its on for an hour in the morning and two hours in the evening, with an extra run on the weekdays around lunchtime, the pipes are well insulated so it means we always have hot water when the taps are turned on.  I am not sure if this is correct or not, but if you have a hot water return it has to be done in Copper, you can't use plastic. Originally our house was going to be done in Hep20 or similar but the plumber ended up doing everything in copper because our local plumbers merchant, which is absolutely excellent for advice,  advised the reg's  stated it needed to be done in copper.

[TerryE]

1 hour ago, Mikey_1980 said:

Originally our house was going to be done in Hep20 or similar but the plumber ended up doing everything in copper because our local plumbers merchant, which is absolutely excellent for advice,  advised the reg's  stated it needed to be done in copper.

 

This might have been the advice from your PM, but it is also not true, so it is bad advice.

 

As to hot return loops, these should not be done in plastic, but this isn't regulation.  Yes, they have a role if you've no control over the layout of your house.  However, no matter how good your insulation is, in practice you are still using your DHW as a secondary heating system.  IMO, not a good idea in a passive house or near spec.  

 

My current farmhouse is a typical layout mess: ~5m from boiler to HW cyl, and then ~9m back to the kitchen.  water takes an age to run hot in the kitchen.  In the new house we clustered all of our wet rooms around a central services cupboard where our DHW + manifolds live.  The path from the SunAmps to the manifolds is <1m and lagged, the average pipe run form the manifolds is 3m or ⅓ ltr which is a couple of seconds running time.  It I'd used 10mm HEP2O for the low flow rans then this would have been closer to a tenth of a litre.

 

[Pete]

I do not think this is correct @Mikey_1980. My last house was a new build which had a hot water return loop and it was all plastic.

[Nickfromwales]

To clarify, pushfit / 'plastic' pipe reduces in pressure rating as temp rises. For central heating, typically 3 bar and below, then this is not a real cause for concern, but when you have a water heater in the picture different considerations get applied. 

Rather than worry about the water overheating ( potentially massively reducing the pressure capability of the pipe and causing the pipe to fail ) we ( WRAS / BRegs ) introduce safety devices to mitigate this. One eg is the T&PRV ( temperature and pressure relief valve ) plus a 5-6 bar cold mains PRV which basically completely remove this consideration / risk from the pipework PoV . 

Plastic 'push / speed fit' pipe can be used on a hot return without issue and whoever advised someone against it is not qualified or knowledgeable enough to have done so.