Changing to a combi boiler - is this realistic?

RainbowLaura

I am thinking of replacing my 25 year old system boiler & hot water cylinder with a combi. The main reason for this is ongoing problems with both the boiler and the cylinder - a new boiler wouldn't solve the cylinder issues and I'd quite like some extra space where the cylinder is located.

However. Although my house is fairly small (about 1000sq ft), it is a 3-storey with 14 radiators. I also like a bath, which I understand can be a sticking point with combis when they are not powerful enough. The boiler would need to go in a kitchen cupboard.

Is this combination of needs realistic? (No pun intended there!) It seems the only combis that would fit inside the cupboard would not be powerful enough. Is anyone able to kindly offer me some advice please? I really want a combi, I know there are down sides but I really don't want to deal with hot water cylinders anymore.

Doozergirl

Why 14 radiators in that space?  A combi boiler is fine in a house of that size but 14 rads is a LOT for a house that size. 

If you're replacing everything else and the radiators are equally as old then you could almost certainly consolidate the number of rads into modern ones that are more efficient and take up less space at the same time. 

I'm not sure where you've picked up your info on combi boilers but most of them fit in a cupboard with no issue and no combi should have trouble running a bath at all.  

The worcester bosch website has a little quiz that will recommend you a boiler based on your house and usage.  That might be worth you having a look to start you off.  

RainbowLaura

Thank you Doozergirl. It sounds a lot, but actually the radiator situation kind of makes sense for the house. There's only one radiator in each room or hallway, apart from the living room/diner which needs the two really. If the number of radiators can't be reduced, I'm thinking a 24kwh boiler would be insufficient? Most of the "compact" ones that fit inside a cupboard seem to be 24.

RainbowLaura

Actually I was wrong, we've got 13 radiators -
3x bedrooms

3x bathrooms

3x hallways

1x study

1x kitchen

2x living room/diner

But still. 13, and no real scope to reduce!

FreeBear

How big is your cupboard ?

Just had a quick look at a random selection of Intergas boilers, and they are 450mm wide by 710-720mm high.

A couple of points to consider...

Ease of routing for a new 22mm gas pipe.

Location of existing central heating & hot water pipes.

Distance to opening windows & doors.

I'm contemplating replacing an old back boiler with a new combi. Will need a new gas pipe laid in and have to replumb the CH to better suit the relocation of the boiler. There will also be a need for a new circuit from the consumer unit so that the boiler has electricity - Much of the work I can do myself to keep costs down.

RainbowLaura

FreeBear said:

How big is your cupboard ?

Just had a quick look at a random selection of Intergas boilers, and they are 450mm wide by 710-720mm high.

A couple of points to consider...

Ease of routing for a new 22mm gas pipe.

Location of existing central heating & hot water pipes.

Distance to opening windows & doors.

I'm contemplating replacing an old back boiler with a new combi. Will need a new gas pipe laid in and have to replumb the CH to better suit the relocation of the boiler. There will also be a need for a new circuit from the consumer unit so that the boiler has electricity - Much of the work I can do myself to keep costs down.

Hmm, food for thought, thank you! 

Our current boiler is slightly smaller than that (Ideal Classic Slimline) and it's a VERY tight fit. I think I might have to suck it up and stick with a water cylinder. 

macman

3 bathrooms and you want a combi? You won't be able to use 2 simultaneously.
For that no. of rads I'd be thinking of a 30kW combi, but your chosen RGI needs to do the maths.
Does each hallway really need a rad? 

ThisIsWeird

Other potential issues with a combi boiler - being mains water driven, a decent flow might struggle to reach the top floor - it depends on your incoming mains flow and pressure, so this needs confirming first.

We have a 30kW combi, and whilst it will, of course, fill a bath, it takes a lot longer than a stored system to do so.

The only truly solid reason I can see for having a combi, is if the cylinder space is required for storage. Ok, it is also nice to have endless hot water on demand without worrying about setting cylinder heating times or recharging if someone pinches it all. Yes, it's also nice to have mains-powered water delivery (tho' you'd also have this with an unvented cylinder). 

When it comes to hot cylinders, you have a choice of vented or unvented - I suspect you know the difference? These will also allow a good degree of future-proofing, or using other energy sources such as solar or PV, so perhaps another reason to keep/renew the cylinder?

The number of rads you have doesn't really matter, as far as I can see; the heating requirement of your house won't be any different with fewer. However, you may wish to consider increasing the size/output of any rad you may be changing, as a larger rad will give the same heat output with a lower water temp, and the lower the water temp, the more efficient your boiler (or future ASHP) will be. So for the main living areas at least - the rooms that will be heated for many hours - see if you can do this. 

casper_gutman

A combi boiler will heat your house just fine. Combis which are sized to meet the hot water demand in most houses are plenty able to deliver the same house's heating needs.

The issue you'll have is running three bathrooms off a combi. With no stored hot water the boiler potentially has to heat water for three taps/showers in real time. No mean feat. 

We have a 30kW Worcester Bosch, and when we put a second bathroom in we went for an electric shower (Mira Azora dual outlet), partly  because we wanted to avoid total loss of hot water in the event of boiler breakdown or disruption to the gas supply, but also because the boiler already struggled to run one shower if a hot tap was opened elsewhere.

benson1980

We had a new (at the time) combi in our last house, which was probably a similar number of radiators to yourself, and two bathrooms but around 1800sq ft. It was 30kw- we didn’t install it but I remember making enquiries when we were buying the house as to whether it was appropriately sized….and it seemed fine.

Anyway, it was ok. Hot water pressure in the upstairs bathroom was an issue. Shower wasn’t great, and we live in an area where mains pressure is very high. We could live with it though.

We have a heat only 17 year old boiler and new unvented cylinder in our current house (similar size), with the cylinder in the loft to free up space in the airing cupboard. There’s no doubt our current setup is a far superior system in terms of hot water pressure to the bath and all the showers. 

Plus we have potential solar options with the cylinder. I also like the fact that the boiler itself is simpler and less to go wrong as it’s heat only.

Running costs in terms of hot water also seem to be a bit cheaper with the cylinder (perhaps because the boiler isn’t firing up sporadically each time there’s demand), and none of us have short showers. To answer your question though if you want a combi (which my wife actually preferred as the whole system was quieter) it should be fine.

ThisIsWeird

benson1980 said:

We had a new (at the time) combi in our last house, which was probably a similar number of radiators to yourself, and two bathrooms but around 1800sq ft. It was 30kw- we didn’t install it but I remember making enquiries when we were buying the house as to whether it was appropriately sized….and it seemed fine.

Anyway, it was ok. Hot water pressure in the upstairs bathroom was an issue. Shower wasn’t great, and we live in an area where mains pressure is very high. We could live with it though.

We have a heat only 17 year old boiler and new unvented cylinder in our current house (similar size), with the cylinder in the loft to free up space in the airing cupboard. There’s no doubt our current setup is a far superior system in terms of hot water pressure to the bath and all the showers. 

Plus we have potential solar options with the cylinder. I also like the fact that the boiler itself is simpler and less to go wrong as it’s heat only.

Running costs in terms of hot water also seem to be a bit cheaper with the cylinder (perhaps because the boiler isn’t firing up sporadically each time there’s demand), and none of us have short showers. To answer your question though if you want a combi (which my wife actually preferred as the whole system was quieter) it should be fine.

Agree with your summary, although I don't understand why you'd have a pressure issue upstairs, if your incoming was good. We have three 'bathrooms' - one has a shower, and the other two have baths with bath/shower mixers. The pressure in the upstairs appears to be just as good as the two downstairs.

The 30kW jobbie gives a great shower, but, yes, only one at a time.