Combi Comparison - any real life experiences?

[thunderstruck]

Hi all,

A gas engineer has inspected my property and suggested that I go with a combi boiler, even though I want to support two showers and a bathtub in the near future.

To compensate, I am now looking at the following two, due to the high flow rates (both with modulation 10:1 - so should be economical):

• Vaillant Ecotec exclusive green IQ 843
• Greenstar 8000 Life 50kW

Had a conversation with a Vaillant approved installer and he told me that I am the first person that mentioned this particular model and he would definitely NOT recommend it given the complexity of it - so I was a bit discouraged.

Anyone has any actual experience with any of these and whether I should go for one over the other - or none of them?

Thanks!

 

[ShaunCorbs]

Yep combi at best one outlet at the same time now if you can see yourself using more than one best to go with an unvented cylinder and heat only boiler

 

[hometech]

There is a very low cost option that will provide the perfect solution. Give each bathroom its own continuous water heater. Around £350 each they will be the best investment you ever make. They can even be fitted on the outside wall so no flue needed.

 

[thunderstruck]

There is a very low cost option that will provide the perfect solution. Give each bathroom its own continuous water heater. Around £350 each they will be the best investment you ever make. They can even be fitted on the outside wall so no flue needed.

Aren't these a massive hit to electricity bills though? Any brands I should be researching on?

 

[hometech]

Aren't these a massive hit to electricity bills though? Any brands I should be researching on?

Gas not electric. Having a high tec combi for heating and back-up DHW and continuous water heater for DHW. Best showers ever..control the flow temp so no mixing down with cold water. Never get fluctuations in water temp either so turn as many cold water taps as you want, still the same output. It's only the UK that is in the dark ages when it comes to wall heaters.....

 

[EvilDrPorkChop]

Hi all,

A gas engineer has inspected my property and suggested that I go with a combi boiler, even though I want to support two showers and a bathtub in the near future.

To compensate, I am now looking at the following two, due to the high flow rates (both with modulation 10:1 - so should be economical):

• Vaillant Ecotec exclusive green IQ 843
• Greenstar 8000 Life 50kW

Had a conversation with a Vaillant approved installer and he told me that I am the first person that mentioned this particular model and he would definitely NOT recommend it given the complexity of it - so I was a bit discouraged.

Anyone has any actual experience with any of these and whether I should go for one over the other - or none of them?

Thanks!

Yeah stay well clear of the GreenIQ. Vaillant have a massive problem with them. Stick to the EcoTec Plus.

But yeah, you need a system boiler and unvented cylinder providing your incoming mains is OK.

 

[thunderstruck]

Yeah stay well clear of the GreenIQ. Vaillant have a massive problem with them. Stick to the EcoTec Plus.

But yeah, you need a system boiler and unvented cylinder providing your incoming mains is OK.

Thanks will do!

 

[thunderstruck]

Gas not electric. Having a high tec combi for heating and back-up DHW and continuous water heater for DHW. Best showers ever..control the flow temp so no mixing down with cold water. Never get fluctuations in water temp either so turn as many cold water taps as you want, still the same output. It's only the UK that is in the dark ages when it comes to wall heaters.***.

yeah never heard of such a set up before, I need to check this out.

May be a bigger job to get gas supply to every bathroom with a shower, but I'll check it out

 

[gmartine]

@ Hometech

I'd be interested to know how many clients you have installed this system on?

 

[Gasmk1]

Gas not electric. Having a high tec combi for heating and back-up DHW and continuous water heater for DHW. Best showers ever..control the flow temp so no mixing down with cold water. Never get fluctuations in water temp either so turn as many cold water taps as you want, still the same output. It's only the UK that is in the dark ages when it comes to wall heaters.***.

Why answer but don’t supply details

 

[Murdoch]

@ Hometech

I'd be interested to know how many clients you have installed this system on?

I'm not convinced he's a registered installer

 

[thunderstruck]

@Murdoch / @Gasmk1 should I not be considering such an option?

 

[EvilDrPorkChop]

@Murdoch / @Gasmk1 should I not be considering such an option?

No it’s a stupid idea 😂

 

[thunderstruck]

No it’s a stupid idea 😂

OK... it's a bit frustrating that I get such different opinions about a simple (in my mind) question.

I have a heat-only set up at the moment, and the engineer that inspected the place told me to go for a combi. Another one told me to go for a boiler system. And I still don't know what to go for.

 

[oz-plumber]

Don't go for a Combi.
Look at the specs of each unit.
Most are done with a 25 C temperature rise of flow rates.

Just assume you need a 40 C temperature rise in winter for a shower, the flow rates drop by 2/3rd's

 

[hometech]

Rinnai news

www.rinnai-uk.co.uk

@ Hometech

I'd be interested to know how many clients you have installed this system on?

I'm a designer, installer and innovator of home automation and communication systems. I am a provider of technology (hardware/software/firmware. I provide answers and solutions to complex problems/needs. As a business I have customers. In a previous professional life (barrister) I had clients. Customers and clients have for too long being used as interchangeable, they are not one and the same.

 

[hometech]

Don't go for a Combi.
Look at the specs of each unit.
Most are done with a 25 C temperature rise of flow rates.

Just assume you need a 40 C temperature rise in winter for a shower, the flow rates drop by 2/3rd's

which is why continuous water heaters are the answer to the informed and educated

 

[John.g]

The "standard" temperature rise, I think, is 35C but quite easy to do your own comparisons.

Continuous Shower Flow LPM = (combi output in KW)X860/60/(required HW temp - cold water temp) so a 30kw combi will give 12.3 LPM from water at 5C heated to 40C, 30X860/60/(40-5), or 17.2LPM from 15C to 40C (summertime), 30*860/60/(40-15). and so on, its quit easy to see that the cold water temperature has a huge effect on the flow rates, also combis with stored water can be a bit misleading as they will only give a continuous flowrate as shown above once the store is used up.

 

[oz-plumber]

which is why continuous water heaters are the answer to the informed and educated

Informed and educated ?

I've installed hundreds of continuous flow units.
They do have their limits and their rated performance is on a 25C temperature rise.
They do perform substantially better than combi units but their downfall is on gas consumption.
Eg: Rinnai 26 ( 26 ltr's per minute at 25C temperature rise ) require 200mJ/h of gas.
They may not need that amount all the time but that's what's on the compliance plate, so the gas line has to be sized to that units plate requirement.

If they are installed without the adequate gas supply, they are not very good at supplying hot water.

Returning to you point about being educated and informed, there may be a lot more knowledge required on your behalf , before you start specifying these units on your clients property's.

If you can install the unit close to the main use taps and gas meter, then feasible.
If you have to run 30m of gas pipe to the units location, then you're up for some added costs.

 

[gmartine]

Rinnai news

www.rinnai-uk.co.uk

I'm a designer, installer and innovator of home automation and communication systems. I am a provider of technology (hardware/software/firmware. I provide answers and solutions to complex problems/needs. As a business I have customers. In a previous professional life (barrister) I had clients. Customers and clients have for too long being used as interchangeable, they are not one and the same.

🤣 Like most legals (former or otherwise) you've managed to say alot without answering the question.