Combi Comparison - any real life experiences?

[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.

 

[oz-plumber]

If anyone wants to know, I have a Rinnai 26 at my place and we can comfortably run 2 showers at once.
Unit is factory set to deliver water at 50C - so no tempering valve required.
( there is an function to increase the water temp by a few degrees - 4C from memory)
I've had the unit for almost 20 years - so I am a fan of them

The problem with 'Hometech's' recommendation to put a unit for each bathroom, is not necessary.
What is necessary is to have the ability to determine what the hot water requirements are for the home and what pipe sizes are required to deliver that hot water.

What 'Hometech' may not understand, is the gas supply requirements.

3 bathrooms - 3 x 26 continuous flow units = 600mJ/h
Gas boiler (24 kW boiler) = 100mJ/h
Gas cooktop = 40mJ/H
Gas log fire = 40mJ/h

Total = 780mJ/h

- Size the gas pipe with that load with an index run of ( say ) 30m

- Size the same gas pipe with a load of 380mj/h ( less 2 HWU's )

Take the cost saving for the labour, equipment & materials into consideration.
There are substantial savings there to allow for a secondary returns system if required.
(House isn't that big - eg. 24 kw boiler

Hope now Hometech understands where I am coming from.

 

[John.g]

Thermally, your unit will supply water at 26 LPM with a 20C rise which = 36.28 kw, so to get water at this temperature requires mains at 30C?? if i am interpreting what the brochure is saying. Also the fuel input is 55kw (199mj/hr) so efficiency a pretty low 66%.
If one uses a average mains temp of 10C then that unit will deliver 13LPM at 50C. or with a showering temperature of 40C, 17.3LPM or just over 8.5LPM to each shower, so unless there are restrictors fitted to reduce the flow to 8.5LPM it just won't work, even using one shower then its still 8.5LPM except you install/remove the restrictors constantly for 1 or 2 shower operation. (8.5LPM would be perfectly acceptable to me)

A 36kw combi will deliver exactly the same flowrates (more efficiently) so except that one doesn't like the complexity of a combi or is heating the house by other means then I can't see any benefit.

 

[exedon2]

Thanks mate.

Seen my oil service guy today cost £260 in total.

 

[SJB060685]

Seen my oil service guy today cost £260 in total.

Thanks mate. Cheaper than I thought.