Why do so many people say not to have a combi boiler in a big house?

SkipFeeney · 28 Feb 2020

I understand a combi would struggle to supply more than one bath / shower but how often do two people in a house have a bath or shower at the same time? We are a family of 5 with 2 bathrooms supplied by a tank, not once have we had two people using a bath / shower at the same time.

I am in the process of buying another house which is pretty large old barn conversion - 2 bathrooms, 4 bedrooms (16 rads). It needs a new boiler and I am tempted to take it away along with the tank etc and replace with a combi with a high flow rate.

Thoughts?

Madrab · 28 Feb 2020

No but if you're in the shower and someone wants to do the dishes and turns the hot water on in the kitchen, or in the other bathroom and wants to wash their hands then you'll soon know about it.

Mottie · 28 Feb 2020

And if the boiler breaks down you have no hot water either - with most vented or unvented hot water cylinders you have an immersion heater that you can at least use to heat the water.

bernardgreen · 28 Feb 2020

SkipFeeney said:
not once have we had two people using a bath

even then filling a bath from a combi can take a long time, and all the time the water already in the bath is cooling down.

Gasguru · 28 Feb 2020

The lack of an immersion heater backup is the overriding reason for not having a combi...imagine Christamas/New Year without hot water.
It happens more often than you think...it's the heating eng. busiest time of year.

And filling a bath for 15 minutes can result in a noticable drop in room temperatures whilst the radiator circuit is out of action.

When you resell the house the new owner will question that choice of combi and consider the costs of upgrading to a cyclinder etc.

Most combis are installed due to the lack of heating installers knowledge (or wanting to keep the quote low) rather than what's best for the family/property.

John D v2.0 · 28 Feb 2020

Yes I'd say the annoying thing is not being able to schedule the hot water for when the heating is not on. You have to shower when the house is already up to temperature really.
We are thinking of putting in small electric unvented heaters for hand wash in the basins as they would allow water draw off immediately and not interfere with the main water draw off. Probably be slightly more expensive due to electric cost and losses but more convenient overall.

JohnD · 28 Feb 2020

SkipFeeney said:
It needs a new boiler and I am tempted to take it away along with the tank etc and replace with a combi with a high flow rate

Getting a new boiler, and getting a combi, are not the same thing.

Gasguru · 28 Feb 2020

And don't buy any of this rubbish regarding higher efficiencies of combis...it's been proved many times there's no difference and was purely a marketing ploy.

I run a boiler each for the DHW and HTG. The DHW boiler tops up the unvented 24/7. The minor heatloss aids clothes drying in the airing cupboard and for 6 months of the year aids heating the landing.
Gas cost is under £250 a year for baths/showers.

bernardgreen · 28 Feb 2020

John D v2.0 said:
the annoying thing is not being able to schedule the hot water for when the heating is not on

Hot water is not scheduled in a combi, the combi fires up when ever it detects water flowing through the boiler on it's way to a hot water tap or shower.

pete50 · 28 Feb 2020

Thoughts? It will be absolute rubbish for all the reasons given. Stick with what you've got.

Elkato531 · 28 Feb 2020

In defence of the combi...
If your incoming cold supply has a good pressure and flow rate, most of the time you'd have no problems and occasionally shower performance might drop off a bit.
You certainly wouldn't want it in a guest house, but for a family who are prepared for a little give and take with each other, no reason why it wouldn't suit your needs.

bernardgreen · 28 Feb 2020

You may have to have new larger diameter gas pipe from meter to boiler to ensure the boiler has enough gas. Often this has to be run along the outside of the house to avoid taking up floor boards etc.

mattylad · 28 Feb 2020

How about 2 combi's then?
One for the heating and kitchen one for the bathroom water?

endecotp · 28 Feb 2020

An issue with “large houses” can be the distance the water has to travel to reach the hot taps.
In particular, you may have a cylinder that is close to the bathroom and kitchen so you get hot water quickly, but a boiler that is further away.
This is something that you may not care about, if your hot water has always been slow to arrive at the taps, or you could find it very annoying!

John D v2.0 · 28 Feb 2020

John D v2.0 said:
the annoying thing is not being able to schedule the hot water for when the heating is not on

bernardgreen said:
Hot water is not scheduled in a combi, the combi fires up when ever it detects water flowing through the boiler on it's way to a hot water tap or shower.

yes, hence the inability to schedule the hot water that I mentioned

endecotp said:
An issue with “large houses” can be the distance the water has to travel to reach the hot taps.

that's a good, point, not to mention the time it takes the boiler to go through it's business and get the hot water actually flowing inside the boiler, which can be the same again as the flow to the taps if not more.

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Why do so many people say not to have a combi boiler in a big house?

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