Effect of replacing 22mm copper with 15 plastic

[MrGatch]

Hi,

I have a large three storey cold Victoria house and I'm having an extension being built which adds a large amount of additional volume to heat. The new space will be UFH and the existing heating system zoned to upstairs and downstairs.

The entire heating system is a single zone in 22mm copper tee'd off in 15mm to radiators. Currently have a 37kW Worcester combi (6 years old) which is being replaced with a Vaillant EcoTec 637 system boiler (+megaflo).

My builders have moved a ground floor riser in the kitchen and replaced about 5m of 22mm copper with 15mm plastic.

The upstairs of the house has always been much colder than downstairs and I've just accepted this. Do I potentially just need to be rebalance the system to fix this?

Since builder has moved the riser, some of the upstairs radiators are now lukewarm, but there is loads of air in the system and some of the radiators are so old they can't be bled so I think I may need to replace them.

Also noticed that if the boiler pressure drops to around 1.1bar then there is practically zero pressure in the highest radiator in the system (nothing comes out when I open the bleed valve, unless I add more water to the system).

I know the 22mm copper has about 3 times the internal pipe area than the 15mm plastic. Should I be worried this? If so, what would the effect be on the upstairs rads? Would this explain colder radiators?

Builder will replace the 15mm plastic with 22mm plastic(!) if I'm not happy but I don't want to waste time/money doing this if it will add no value.

Thanks,

 

[Riley]

Filled with dread at “my builder has done xyz” was a plumber involved? Who fitted your new boiler? Was the system flushed? Who fitted the megaflow, have they upgraded your mains feed and tested pressure and flow? Sounds like they have cocked up the pipework as 15mm and 22mm pipes will only be able to carry a certain kw. Sounds like this hasn’t been sized appropriately to accommodate the new House heating requirements. Sorry to sound negative but plumbers don’t build walls builders do hence why builders don’t size heating systems

 

[MrGatch]

None of the heating changes have been made yet apart from moving the riser. Its all proposed at this stage.

The heating engineer has seen the plans and the house and seems pretty competent and thinks that the EcoTec 37kW and a Super Oso cylinder is adequate for the heating and UFH.

However its the builder who has moved the riser as part of knocking through a wall - plumber / heating engineer not consulted.

I suppose what I am asking is will a 5m section of previously 22mm copper that is now in 15mm plastic have a noticeable impact on the heat output in the 9 radiators above it on the upper two floors?

Thanks.

 

[Riley]

Who designed the system??Without knowing the exact heating requirements above (room sizes, double glazing etc) I’d say it should be a MINIMUM of 22mm, personally I would get the heating engineer in NOW to ensure all pipe runs are adequate for your requirements. It’s a damn site easier to alter pipework now rather than when you are turning on the new boiler for the first time

 

[Riley]

Also has anyone tested that your mains is suitable for an unvented cylinder

 

[SimonG]

Your builder has fecked it. Unless it was just a temporary measure to get him away. Builders and pipes don't mix.

Either way it needs to be changed back to 22mm copper.

 

[MrGatch]

Having a brand new water main fitted in 25mm MDPE direct off the 6" main in the street (asked for 32mm, but they said no). Am assuming this will be okay with the megaflo, but there is no way to tell. I'd be surprised if it wasn't.

The water main and gas main are both being replaced and every component on the heating/water system replaced so its impossible to know how it will behave. The only bit to stay the same is the existing pipework (22mm heating, 15mm hot/cold water) with the new hot and cold runs to the riser being in 22mm.

If I ask the builder to re-do the 5m heating stretch in 22mm plastic (which is about 25% smaller cross-section area than 22mm copper?) then I think he'd do that. He hasn't quoted for 10m+ of copper pipe in his quote which means I'll end up having to pay for it. No problem paying this unless the heat difference between the 22mm plastic/copper is marginal - definitely not cutting corners.

I did wonder whether the capability of the pump in the old boiler might have some input into the temperature of the upstairs rads.

 

[Riley]

I’d be asking the water board for some pressure and flow assurances. They should be able to provide you with rough figures. Likewise the plumber should be able to test pressure, flow and dynamic pressure so you know what you have currently. Sounds like a lot of finger in the wind to me.

How many bathrooms do you have/will you have?? As 15mm hot and cold seems undersized. This will be coming off the unvented cylinder so should really be run in 22mm prior to downsizing at sanitary ware. If you have a hot water demand over a number of floors then a secondary return pump on the hot water side would prevent a lot of wastage
I think you need to revisit the pipe sizing.
Again who designed the layout?
It sounds like this really needs some re-thought.
The pump in the old boiler could be an affecting factor although heat does rise.

 

[SimonG]

Separate pumps for each zone and the plastic will be throttling the heating more than you think due to the inserts in the pipe.

Don't get the builder to do the pipes get the plumber. Tell builder it's coming off his Bill for screwing it up.

 

[Scott_D]

How many radiators on the changed pipe?