Garage conversion - combi boiler suggestions

[akist]

Stupid questions time, do I take it that the water that the combi system circulates through the radiators is separate from the water it feeds to the taps around the house?

Also, when a user turns a hot tap on, the system wakes up and starts heating that water so after a while the hot water reaches the tap?

And the user can adjust the hot water max temp to say, 70C?

And finally the maximum "strength" of the boiler is given in the specs, ie what is the max water flow rate it can heat up from X to Y degrees? And if CH is on it automatically gives priority to HW?

 

[Dan Robinson]

I take it that the water that the combi system circulates through the radiators is separate from the water it feeds to the taps around the house

Yep

when a user turns a hot tap on, the system wakes up and starts heating that water so after a while the hot water reaches the tap?

Yep

And the user can adjust the hot water max temp to say, 70C

Usually the max is 60. But the magic number is 35° rise from whatever the incoming is at the rated flow rate.

maximum "strength" of the boiler is given in the specs, ie what is the max water flow rate it can heat up from X to Y degrees

Yep. All combis are a compromise. But if showers are the primary hot water demand then there is no point going beyond the two lower outputs.. My recommendation is the Intergas Eco RF 24 or 30 or Intergas xClusive 24 or 30

And if CH is on it automatically gives priority to HW

Yep.

 

[bernardgreen]

Shows how hard you looked [for flow rate].

One chart has the statement 12 l/min

There is a scale for Fan Speed and a scale for Temperatures. Where is the scale for flow rate ?

There is a binary state indicator for Tap Switch

Dynamic pressure and flow remains the same when the cisterns are filling does it?

No they do reduce slightly.... but do not noticably affect the shower

 

[Dan Robinson]

is The rest is easily deducted from the charts

No they do reduce slightly.... but do not noticably affect the shower

What's good for the goose is good for the gander.

 

[bernardgreen]

12 l per min CONSTANT FLOW, and one can assume the temperature of the water arriving a the boiler is constant

What would the temperature graph for the hot water temeprature show if the flow rate was reduced fro 12 to 6 l per min.

Would there be a transient rise in temperature ? How long before the boiler modulates down to match the reduced heat load and the temperature returns to the required value.

 

[Dan Robinson]

Boiler matches temperatures perfectly adequately.

Seeing as you're such a smarty pants I'm sure you can use physics and fan speeds to extrapolate all your answers.

 

[bernardgreen]

Boiler matches temperatures perfectly adequately.

Inadequate answer.

Agree a change in fan speed will ( should ) occur when water flow rate changes. How long before the boiler reacts and changes the fann speed. ?

Unless there is a flow meter in the DHW circuit the only information available to the boiler controls about flow rates and hence the amount of heat needed is the change in temperature of the DHW leaving the boiler when the flow rate changes.

 

[akist]

As I was following the links suggested to me above, I came to this

and this

https://www.canetis.io/products/super-flow/

 

[flameport]

https://www.canetis.io/products/super-flow/

An overpriced solution to a problem no one ever had.

Evidently the designers of that thing haven't heard of a storage combi boiler. Or much else.

 

[ianmcd]

Forget |Bennyboys arguments, he hates combis, a properly installed Combi will be more than adequate for your requirements

 

[ericmark]

I have a Worcester Bosch which has an Eco button, with the Eco button on it does not store hot water, using the shower it starts cold and slowly warms up then works A1 once running, but with Eco off it stores a little water, and the shower slowly heats up, then cools then heats a second time and stays hot.

The kitchen taps with Eco off seemed to work OK, but with Eco on we would not get any hot water, well every so often it worked, but most of the time it stayed cold. I removed kitchen tap since also low output, and found the hot flexible feed pipe kinked, on correcting this I found the kitchen taps worked equally well Eco on or off.

With other house we have a Main 7 domestic water heater, before combi boilers came out, that also has a problem, unless the hot water used is over a set figure, then it can go cold, talking about 1982 technology, we found if we used a shower head for an electric shower it did not use enough water and would turn cold, as long as a large shower head was used, then no problem.

So yes with a combi boiler there is a lower limit which if your not drawing enough water it will go cold, and it can have a cold spot soon after turn on if Eco is not switched on, and you can only run one shower at a time, and if some one runs hot tap it can go cold, however in the main I would say far better than an electric shower and in a house not a problem, you know running water while some one is in the shower makes it go hot/cold so you don't do it.

 

[bernardgreen]

Forget |Bennyboys arguments, he hates combis,

I dislike the mis-selling of combi boilers, they have ther place, in flats and very small houses designed with no space for hot water storage.

 

[ianmcd]

read the OPs first post, he is converting his garage to a one bedroom one bathroom granny flat, I have a 4 bed 14 rad house with one bathroom and one en-suite and have had a 28 KW combi for 15 years and when it fails it will be replaced by another combi, never ran out of hot water ever

 

[akist]

Does the combi boiler need (a) circulating pump for CH (b) expansion vessel (c) anything not included in the package?

 

[Gasguru]

You've not explained who might be staying in the annex...if they are elderly or infirm I would certainly not entertain a combi.