Combi Comparison - any real life experiences?

[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.