Is this feasible - 2 combi's in one home.....

[r6deano]

Afternoon people!

Any advice much appreciated please, here's my dilemma-

I'm renovating our new home, it's currently a 3 bed detached bungalow, with a room in roof. It's soon to be (subject to PP!) a 4/5 bed. The conversion will mean the removal of the current vented system, and an old old oil boiler.

So I have a clean slate when it comes to selecting a new system.

I may not end up with loft space, just eave space, which points towards a combi, although I've been recommended a pressurised cylinder system to handle the demands of a larger home (albeit there is only the 2 of us and a baby on the way) as opposed to a combi which may struggle beyond 3 beds and 2 baths. But reading up on the pressurised boiler systems, I'm not too convinced.

So I'm wondering whether I could install two combi's-

One to supply the upstairs 3 beds, bathroom (shower bath), ensuite (shower) and heating (5-8 rads)

And one for the downstairs kitchen, lounge, family room, 2 beds and small shower room? With underfloor wet heating in kitchen/family room, and maybe 4 rads?

Also giving a back up of hot water/some heat in the event of a breakdown.

Thanks in advance for any thoughts/tips.

Deano

 

[stardanny]

Not a good idea to have two combi.

Better to have a system boiler and unvented hot water system.

It is all depend on your incoming water main pressure and how much litres per minute it can supply.

Best to ask your plumber to advise you.

Daniel.

 

[BigSnoopy01]

bad idea really unless you are going to upgrade your gas meter/supply. go for the unvented cylinder option, design a good sized cupboard into the plans.

 

[PullerGas]

While unvented cylinders are great, pressure & flow rate permitting! Modern Combis perform very well, a 35-40KW would most likely meet your requirements in a house of that size. Employ the services of a good Plumber & Heating Engineer, don't do it through the Builder/Main Contractor, they'll have any old idiot on site.

 

[Twenty Four]

don't do it through the Builder/Main Contractor, they'll have any old idiot on site.

Unless you're busy elsewhere of course.

 

[PullerGas]

don't do it through the Builder/Main Contractor, they'll have any old idiot on site.

Unless you're busy elsewhere of course.

After many years of sub-contracting to hairy arsed Builders, I can assure anyone there's very few good ones & even less honest ones. Most will just sub out to anyone with the cheapest price & I mean anyone!!
I can only recommend that anyone having Builder work done has a Small Works contract in place & has their Architect supervise the project.

 

[Agile]

Before getting far with any planning you need to know the dynamic flow rate of your mains water.

Both combi and unvented depend on mains supply.

A single combi and unvented cylinder is often a good combination.

Tony

 

[muggles]

As above, unvented is the way to go here, two combis means twice the amount of maintenance for a start

 

[RTFB]

The really crucial thing is the dynamic flowrate of the cold water main. Go for a single powerful combi if you like the idea. A 35kW combi with a good water main behind it should drive two suitable combi-compatible showers. The disadvantage to fitting a combi plus an unvented cylinder is that you cannot then fit the boiler with weather compensation, which is the best form of control for a condensing boiler.

 

[r6deano]

Not a good idea to have two combi.

Better to have a system boiler and unvented hot water system.

It is all depend on your incoming water main pressure and how much litres per minute it can supply.

Best to ask your plumber to advise you.

Daniel.

Hi Daniel,
Thanks for your reply. I'm told the mains pressure isn't great (will have to find out the incoming flow rate).

I was thinking two combi's to remove the need to find a space for the cylinder, although I may have extra loft space (depending on planning permissions say so)

Cheers!

 

[r6deano]

bad idea really unless you are going to upgrade your gas meter/supply. go for the unvented cylinder option, design a good sized cupboard into the plans.

Thanks BS. It's oil fired, whether that makes a difference?

The boiler will be at the back of the garage, and potentially I could put a cylinder above in the loft space (so long as planning approve me to replace the flat roof to pitched)

Cheers

 

[Dan Robinson]

On oil it's an even worse idea. Small boiler working hard and a 210 litre cylinder will be best. Possibly with a secondary return depending on floor plan.

 

[r6deano]

Before getting far with any planning you need to know the dynamic flow rate of your mains water.

Both combi and unvented depend on mains supply.

A single combi and unvented cylinder is often a good combination.

Tony

Thanks very much Tony. Possible silly question time - what's the best way to determine the flow rate - is it something I can do myself? Appreciated.

 

[Agile]

See the FAQ on how to measure dynamic flow rate.

 

[Agile]

The disadvantage to fitting a combi plus an unvented cylinder is that you cannot then fit the boiler with weather compensation, which is the best form of control for a condensing boiler.

Are you not familiar with the better boilers on the market now?