Combi capacity

[dunc_r]

I'm comtemplating a combi boiler, but my only experience of them was hopeless hot water flow - but I'm going back a few years!

Question is this - can a modern combi successfully service a 5 bed house, (2300 sq ft.) with 15 rads, two baths & a pumped shower?

Thanks in advance.

 

[kevplumb]

you can't pump a shower off a combi

 

[Paul Barker]

Doesn't matter about size of house, it's the two bathrooms and pumped shower which are the problem.

Sounds like a new gravity hot water cylinder and a condensing regular boiler, accompanied by a proper system clense and bringing of system up to modern standards would suit you better.

 

[gas4you]

As Paul says or change to an unvented mains pressure cylinder and remove shower pump. I would recommend one around 210/250 litres. This would give you mains pressure at all your hot taps.

You need to have good incoming cold mains pressure though, over 3 bar ideally and a 22mm cold supply to cylinder. It would also need to be fitted by a registerd un-vented installer. Not a diy job

 

[dunc_r]

Thanks all. The current h/w cylinder is good - under a year old - but the issues I need to address are low hw pressure in the bathroom (only 2m head, which is severely restricting her indoor's choice of taps for a refit) and an ancient boiler ( potterton floorstander, c. early '80's).

Bear witrh me, more questions: am I right assuming an unvented hw cylinder also does away with the cold tank in the loft and gives mains pressure to cold taps also? Is it typically a big job to swap a system from vented to unvented?

Is a 'whole house pump' on the exiting gravity system a silly idea?

The current boiler is in the middle of the house with a vertical flue approx 6 metres to a roof vent. Is this practical with modern condensing boilers?

Thanks again.

 

[gas4you]

Changing to un-vented can be a big job depending on the siting of the cylinder.

Cold mains pressure to cold taps has to be balanced for showers, baths etc. This is acheived by 't' ing off the unvented cyl cold supply after the pressure reducing valve.

Kitchen cold etc will usually remain as is.

yes it will do away with the cold tank in loft as would a system boiler for your heating F&E tank.

You could have a domestic hot water boost 'bronze' pump fitted, although these are relativley quite expensive.

if your current flue is a purpose made boiler flue then the new condensing boiler flue can follow the same path with its new flue and flue terminal. If your existing one goes up inside a lined chimney then no it can't.

Remember to think about condensate drain off boiler. You can fit a condensate lift pump if needed if you have not got easy access to a drain from original position. Same applies to the safety drain if you go for a system boiler. This has to have a continuous drop to outside.

 

[dunc_r]

Thanks Dave - last question - the existing flue isn't in a chimney, it looks like an asbestos pipe about 6" diameter with a couple of right-left 45 degree turns to line it up with the roof. Is balanced operation possible through such setups?

 

[gas4you]

No. All new boilers need to have their own specific flue fitted. Most will have a vertical option and these days are very flexible with their flue options. You will have to check waht the maximum equivalent flue length they can work with. Some offer the option of fittin a larger diameter flue to get over longer distances. Each 90D elbow adds 1M to the flue length