Running a second boilerfrom same water supply

[geeman028]

Hello all, new to the site and hoping I can get some help while I do my extension.

I'm currently in the process of building an extension on the side of my house (joined to current property)
I've built a sort of granny annexe with a kitchen bathroom and livingroom/Bedroom.

I'm planning on adding a combi boiler to the new build instead of tapping off my current regular boiler.
a: So new build can have control over their heating, and
b: I think current boiler not big enough to run the extra rads that will be added.
Both will be run off same water and gas supply.

I have been told in passing conversation that the water supply will probably drop when the original property runs their taps. Does anyone know if this is true and if so will a pump fix this problem. Also does anyone know of any other problems I may encounter with this installation.

 

[oz-plumber]

Of course its true.

It depends on the incoming mains pressure and flow rate.
Combi Boilers lose pressure due to their design - unavoidable.

Pumps will not help unless there is sufficient water supply available from the mains.
You may need some expert advice regarding what you are trying to do.

Try and get it prior to doing all the work, will cost you triple or more to rectify one the work has been done

 

[geeman028]

Thanks for the reply.
There is currently a water feed/tap in there which I was going to use as the feed.
I will get a water pressure tester and check it.

Do you know what minimum pressure is required to run a combi?

 

[Riley]

Absolutely true !!! No doubt you will be enlisting a heating engineer to install your boiler(s) so I would get them to check your incoming mains and to recommend a solution, be it upgrading and splitting your incoming main or installing a more suitable system

 

[Howsie]

There will be minimum water and gas pressures required. Get someone in to have a look and discuss your options, keep your mind open at this stage or you'll go down the wrong route for the wrong reasons.

 

[Riley]

Thanks for the reply.
There is currently a water feed/tap in there which I was going to use as the feed.
I will get a water pressure tester and check it.

Do you know what minimum pressure is required to run a combi?

It is very dependent on the boiler you want as manufacturers vary. What boiler is in the existing property ? Combi? System? Open vented?

The key with your flow and pressure is when multiple outlets are open, then what happens to the amount of flow at outlets. Rather than guess it and get it wrong I would strongly recommend you get a professional in

 

[geeman028]

It's a regular boiler currently in house. With the cylinder in airing cupboard and tank in loft.

I've ran tap outside and opened other outlets and didn't notice a drop really.

Yes I will be getting a professional in in the near future but was just asking on here to get some advice /ideas.

Thanks again.

 

[Riley]

In the existing property are all of your cold taps mains fed or CWSC fed?

 

[geeman028]

They all run off the mains water supply.

 

[Riley]

Well look at it this way in the unlikely event that you have all the cold water taps open in your property and then they try and get hot water in the Annex there may not be enough flow/pressure for the boiler to function. You really need to get the flow and pressure and dynamic pressure tested properly. The other factor to take into account is if you then upgrade your existing boiler to a Combi or unvented system you could be knackered. Surely better to future proof yourself now and get your mains upgraded just so you know you don't have to rip up floors once your building is complete

 

[geeman028]

Thanks for the advice guys. Much appreciated. Given me a bit to think about anyway. I'll get a few plumbers in and let them have a look at my plans. See what they come up with.

 

[kris]

Yeh defo need all pressures n pipe lengths etc all measured and calculated to get exact answer but dont be surprised if you need new pipework ran in further than you thought to cope with drops, quick question is the annexe gonna be self sufficient and contained ? as if not and its just an extension to whats there it might be cost effective to upgrade existing to cope with whole house ?

 

[geeman028]

Was hoping to have new build self contained, that's why I was thinking of the second boiler route.

 

[Riley]

If you're talking in terms of hot water then maybe just increase your existing cylinder. If you're talking heating just link to existing and zone the extension with the annex having its own thermostat