Combi Vs Combi Storage

eboarde

Hi,

I'm looking at replacing a very old oil fired boiler with a gas boiler (I've already got gas piped to the house) and I'd love to get rid of the hot water tank as well (its taking up a lot of space I could use). Therefore I've looked at combi boilers but recent advice is that I may need combi storage boiler. There are only two of us in the house most of the time but we have 3 bathrooms and get a lot of visitors. What do you think? Is the combi storage significantly less efficient that the combi? Is it possible to turn off the storage when we don't have visitors? Anything else I should consider?

Thanks,

Eboarde

heinbloed

Is the combi storage significantly less efficient that the combi (-boiler)?

Yes.

Is it possible to turn off the storage when we don't have visitors?

Yes.

Anything else I should consider?

Get the thermal demand calculated (EN12831). Pay for it.

Any gas combi storage boilers I have worked on hasn't had the ability to turn the storage side off.

The first question should be is the mains water suitable to run a combi boiler.

Combi storage boilers are ok but they can have their own problems, with the performance of modern combi boilers on good mains water you will get decent hot water without paying for stored water you may not use.

Why were you advised a storage combi?

DGOBS

assume it was cos they have 3 bathrooms, so assume beyond the demand of a 'non-storage' combi.
Also, most of the storage ones I have worked on a pretty big size wise anyway, if I was going down that route, think I would opt for a heat only boiler and put in a Rianni water heater to suit such a high demand (with no required storage) cost wouldn't be a whole lot more (most good storage combi's are pretty expensive)

DGOBS

DGOBS wrote: »

assume it was cos they have 3 bathrooms, so assume beyond the demand of a 'non-storage' combi.

Still a square peg in a round hole compared to a stored water design, you will get a bath out of the stored water then it's a combi, you can end up with a shower that can only work if the stored water is up to temp.

eboarde

Thanks for all the replies.

I was advised to go for the storage combi as we have three bathrooms.

My mains pressure isn't great but I'm told you can put a pump on the inlet and feed from the cold water tank in the attic.

The Rinnai heater looks interesting.

In general the hot water demand is quite low as there are only two of us.

Thanks again.

Using a storage combi or combi without decent mains to me means a combi is not suitable for you, you can store cold water in a break tank and pump it but I find it's rarely done correctly as the stored water doesn't match maximum water requirement which can cause problem if the storage tank ever emptys.

In general a storage combi will keep the stored water hot all the time so at night you can hear it firing to reheat the clorifier, the stored water can be at a temperture that is quite high and then reduce to a much lower temperture if you don't reduce the flow of the water at the hot tap, a storage combi must be fitted to G3 water regs(for your safety) which they never are, the expansion vessels have a tendency to give trouble, if the system water isn't spotless the coil in the clorifier can block leaving you with no heating, the storage vessel tend to have sacrificial anodes that require checking every year that often don't get checked leading at times to leaks.

I'm not against stored combis as they work very well when done right with good mains pressure, they just need a little more love than a combi, I have seen a lot of jobs where stored combis have not worked or preformed badly due to installations errors.

I think the best systems are the simplest and a good combi with a decent flow rate would give you a quiter life than a storage combi from my experience.