Combi Comparison - any real life experiences?

[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.