Reducing my pipe size

[anta]

Hi all,

We have a gravity fed hot supply to our bathroom, currently all in 22mm pipe. We're about to completely gut the bathroom and replace it with a new suit, new tiling, etc. The bathroom is about 15m from the hot water cylinder, and with 22mm pipe it takes ages to get hot water in the bathroom. If I replace the pipe with 15mm then there's less metal to warm up, and less water in the pipe to flush through each time, so moving to 15mm would seem to solve our problem.

Will I get pressure drop problems? I don't want to slow down the bath fill rate too much, though I would accept it being a bit slower to fill if the hot water arrived sooner. As I understand it most modern bath taps are on 1/2BSP fittings, so will 15mm for the entire length make much difference to the fill rate over same taps but 22mm pipe?

All help appreciated
Ant

 

[seco services]

most modern bathrooms are on mains pressure so 15mm ok.
i wouldn't change gravity to 15mm on bath leave at 22mm

 

[TicklyT]

Many modern bath fillers use 1/2" fttings because they are designed for mains water pressures much higher than a gravity system. If you have a combi or unvented system thats no problem, but they don't work well on a gravity system.

22mm gravity system pipework will deliver water at about twice the rate of 15mm pipe.

 

[JohnD]

gravity fed bath taps fed by 15mm pipes, you will need a book to read while waiting for the bath to fill.

invest in some climaflex or similar pipe lagging as well.

 

[bengasman]

you don't get enough hot water through and you want to make the pipe smaller? that is a rather unique solution.
doubt it will solve the problem though

 

[anta]

you don't get enough hot water through and you want to make the pipe smaller? that is a rather unique solution.
doubt it will solve the problem though

Er - not quite. We do get plenty of hot water through, but it takes 3 or 4 minutes (literally) for anything warm to arrive. I can fill the basin sink about 8 times before it's warm enough to wash with.

Point taken on the 22mm to the bath. How about this alternative. Leaving the bath supply as it is, the basin already has 15mm for the last couple of metres (under the bath to under the sink). Is it worth running a separate 15mm back to the tank for the basin on its own?

Ant

 

[seco services]

Point taken on the 22mm to the bath. How about this alternative. Leaving the bath supply as it is, the basin already has 15mm for the last couple of metres (under the bath to under the sink). Is it worth running a separate 15mm back to the tank for the basin on its own?

Ant

no not really

 

[bengasman]

how long does it take for the bath to start giving warm water?

4 minutes seems awfully long.

could it be there is a gatevalve half closed somewhere?

 

[anta]

how long does it take for the bath to start giving warm water?

4 minutes seems awfully long.

could it be there is a gatevalve half closed somewhere?

No valve. I've checked. Bath is not so long, but mainly because the flowrate is greater. It also matters less on the bath. We just put the plug in and turn on the tap. Cold water at the start is the same as cooling ti with cold when its full, so that's fine. It's really really annoying on the basin though. I usually turn the basin tap on, have a shave, and put the plug in and fill the sink. My theory was the relatively low flow rate means it takes ages to empty the cold water from the 22mm pipe before any hot arrives, so moving to 15mm would reduce that volume of water, therefore making it happen quicker for the same flowrate.

Ant

 

[bengasman]

so how long does it take for the bath to get warm?

if there is no gate valve at all, how do you change a washer, or a tap?

 

[anta]

so how long does it take for the bath to get warm?

Say 1 to 2 mins. Definitely less than the sink, but still a reasonable amount of time. There's a lot less delay in the kitchen and utility but they're either side of the tank in the circuit so the distances are a lot smaller.

if there is no gate valve at all, how do you change a washer, or a tap?

There's a gate valve between the header tank and the hot cylinder, but none between the taps and the cylinder. Drain the hot cylinder down I guess. We've not had to do it yet. This is a 1971 bungalow which we've lived in for about a year now.

Ant

 

[bengasman]

gate valve before the cylinder will slow it down just as much as one after.
if the bath fills up in about a minute, that is probably not the culprit.

did a quick calculation, and came to educted guess that every time you use the basin enough to actually get hot water, you are wasting about 30 litres of hot water, and 60 litres when you use the bath.
maybe it is an idea to relocate the cylinder.

 

[JohnD]

I have seen a method used, with a return loop between cylinder and bathroom, so hot water can circulate and keep the pipes hot. It would be wasteful of heat, though, so you'd need very good pipe insulation.

I don't know if it's considered acceptable practice these days, because of the heat wastage.

 

[gigz]

Could be limescale/crud at the cylinder outlet. If you loosen the 22mm nut on the top of the cylinder (isolate or bung the tank) gently move pipe aside and scrape it out to full bore.

 

[blondini]

Here's a thought. (After you've scraped out that crud). Plastic.

Replace the 22mm copper with 22mm plastic. Plastic won't soak nearly as much heat out of the water during the initial flow and thus it will improve warm up time at the tap. Try to do it in one continuous length from tap to tank as this will assist flow rate.

You don't need a high flow rate on the basin tap, so good idea, why not run a separate feed back to the tank in 15mm. Do it in plastic for same reasons as above. The flow rate may be halved compared to 22mm, but since the volume of water in the pipe is one third, the hot water will still get there quicker and with less wastage. 15mm Plastic is so easy to work with, you could easily lash up a temporary length to see what difference it makes.