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.

 

[Gasmk1]

Nothing new in multipoint boiler combo we did that in uk during the 60’s and 70’s, before comb is invented, but using both now would be 2 or 3 flues increased gas pipework and possibly increase to u 16 meter

 

[gmartine]

Mods, is there any relationship between this Rinnai fan boy and that other member (or two) that espouses their use?

There is some familiarity in their sheer arrogance as well as bloody mindedness and I assume that multis are not allowed.

 

[SJB060685]

Mods, is there any relationship between this Rinnai fan boy and that other member (or two) that espouses their use. There is some familiarity in their sheer arrogance and bloody mindedness and I assume that multis are not allowed.

Something doesn't add up does it.

 

[gmartine]

There's certainly a familiar ring of supreme being about this poster but why he needs to hang around this uneducated pleb hole for confirmation I do not know. 🙂

 

[hometech]

No it’s a stupid idea 😂

Can I take up a challenge for charity with you! You provide proof to the group (pictures of installations you have made and testimony from the customers who subsequently had them removed). For every proof you provide of the install/remove cycle, together with verifiable testimoney, I will pay £1000 to a charity of your choice. I will have to set a limit of £10,000 (so maximum 10 customers). I will have a chat with some people from my former chambers who will validate the details and handle the legals....Over to you

 

[hometech]

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.

so you know that you set the water temperature right... so you know that you only heat to the temperature you desire and not above that to then mix down. So 26l per minute would be a great water flow into any property...but the average is much lower..you know that too right! As for output in terms of heated water. The lowest recorded temperature for mains water was recorded in 2001 @ 4.9 degrees. So lets take the worst ever situation and raise that by 25 degrees. That would give a flow temp of 30 degrees @ 26l. The average shower temp is between 32-35 degrees. If the average home does not have 26l input. how can it achieve that as an output. Perhaps you are confusing measurement sizes with Australian. 30m gas pipe in an average UK home? Do you mean stately homes?

 

[SJB060685]

@hometech I'm just curious, what tickets do you hold relevant to the plumbing and heating industry? This is not me being rude, or trying to belittle you in anyway, I'm genuinely curious. A lot of the engineers on this forum have been doing this for decades, it's seems stupid to argue with their advice.

 

[oz-plumber]

so you know that you set the water temperature right... so you know that you only heat to the temperature you desire and not above that to then mix down. So 26l per minute would be a great water flow into any property...but the average is much lower..you know that too right! As for output in terms of heated water. The lowest recorded temperature for mains water was recorded in 2001 @ 4.9 degrees. So lets take the worst ever situation and raise that by 25 degrees. That would give a flow temp of 30 degrees @ 26l. The average shower temp is between 32-35 degrees. If the average home does not have 26l input. how can it achieve that as an output. Perhaps you are confusing measurement sizes with Australian. 30m gas pipe in an average UK home? Do you mean stately homes?

Perhaps all the bright ideas that you have alluded to your vast new found knowledge regarding plumbing, have been common knowledge for most plumbers for 20 odd years.

By the way, average shower temperature is 43C.
Why would you shower in water colder than your body temperature?

As for temperature setting devices, they are rarely installed anymore.
Who wants to set a temperature every time they open a tap.
If you have multiple pads in a house, you have to check them, because the unit will only heat to the lowest set temperature. You have to make sure the bathroom pad is switched off after use, because it over rides all other pads and the other pads cannot be altered if the bathroom pad is 'on'

Stately Homes?
I'm doing a 2 bedroom, 1 bathroom terrace at the moment.
Gas pipe length from gas meter Rinnai 26 - 25m in total ( index length )
On the way there is a 12 kW boiler and gas cooker.


That' enough information for you to work out the gas pipe size from the gas meter to the Rinnai 26.

Assumed, acquired, guesstimated knowledge will always be outdone by educated and practicable knowledge.

 

[hometech]

Perhaps all the bright ideas that you have alluded to your vast new found knowledge regarding plumbing, have been common knowledge for most plumbers for 20 odd years.

By the way, average shower temperature is 43C.
Why would you shower in water colder than your body temperature?

As for temperature setting devices, they are rarely installed anymore.
Who wants to set a temperature every time they open a tap.
If you have multiple pads in a house, you have to check them, because the unit will only heat to the lowest set temperature. You have to make sure the bathroom pad is switched off after use, because it over rides all other pads and the other pads cannot be altered if the bathroom pad is 'on'

Stately Homes?
I'm doing a 2 bedroom, 1 bathroom terrace at the moment.
Gas pipe length from gas meter Rinnai 26 - 25m in total ( index length )
On the way there is a 12 kW boiler and gas cooker.


That' enough information for you to work out the gas pipe size from the gas meter to the Rinnai 26.

Assumed, acquired, guesstimated knowledge will always be outdone by educated and practicable knowledge.

I never mentioned shower temp in my response so why obfuscate?
Maybe you can explain to the shareholders of the worlds largest manufacture (by volume) of wall hung heating devices that there is no market for their product (despite sales in the millions each year lol)
You set the temp as a default and then change it if required....but you know that right, you have installed hundreds of them?
And then you contradict yourself..
The average 2 bedroom property in the UK is 6m in length and 4m width (new build) 2.3m ceiling height. How on earth can you get 25m?
I'll call you....Double first, GDL, BPTC and 38 years of electronics and patent litigation experience...lets' see your hand?

 

[oz-plumber]

So lets take the worst ever situation and raise that by 25 degrees. That would give a flow temp of 30 degrees @ 26l. The average shower temp is between 32-35 degrees.

I never mentioned shower temp in my response so why obfuscate?

???????????????????.

You did mention shower temperatures

Who's Obfuscating?

( I did have to look that one up )

No hard feelings.
I just read what you wrote and replied to what you wrote.

 

[Gasmk1]

???????????????????.

You did mention shower temperatures

Who's Obfuscating?

( I did have to look that one up )

No hard feelings.
I just read what you wrote and replied to what you wrote.

Come on he has loads of letters after his name he obviously knows more than us leave him to it.

 

[exedon2]

Surely all qualifications have to be seen I context?
I've a hnd (construction) and have held a G6 welding ticket non of which has any relevance when I'm fitting a oil boiler!

 

[SJB060685]

Surely all qualifications have to be seen I context?
I've a hnd (construction) and have held a G6 welding ticket non of which has any relevance when I'm fitting a oil boiler!

I don't suppose you have current vapourising tickets and if so what does that cost?

 

[exedon2]

I don't suppose you have current vapourising tickets and if so what does that cost?

My oil service guy has just renewed his vaporising ticket will ask him tomorrow.

 

[SJB060685]

My oil service guy has just renewed his vaporising ticket will ask him tomorrow.

Thanks mate.