Combi DHW flow rate - sufficient?

eamon

35-38 celcius is the new standard for bath/shower mixers. Its related to the anti-scald campaign that is currently under way. Its comes factory set. It is possible to overide this function. Addditionally some of the manufacturers are suggesting that these units be serviced every 12 months. As it happens though this appears to be more a case of removing the dirt filters and giving a good clean.

C_Mababejive

OP i presume you have an existing hot water storage cylinder? how old is it/what condition/is it insulated/where does it live?
Many heating engs will automatically sell you a combi but they are not a panacea....
There is much to be said for stored hot water and you can buy a high efficiency system or conventional boiler which is a lot simpler yet still efficient with good flow rates to ALL taps..

ey_up

C_Mababejive wrote: »

OP i presume you have an existing hot water storage cylinder? how old is it/what condition/is it insulated/where does it live?

Unfortunately the cylinder is very old, not insulated and lives in an upstairs room. I think the whole system is circa 20 years old minimum.

C_Mababejive

I wonder if you are having a new shower enclosure installed and if so,do you expect it to be of the mega,powershower variety?

If so,you might consider a pressurised hot water cylinder.

I think the tide is turning on combis and more well informed people are returning to stored hot water..

ed110220

I think the tide is turning on combis and more well informed people are returning to stored hot water..

Why is this? What are the advantages and disadvantages?

I'm in a slightly similar position. My new house has a boiler behind the fireplace downstairs with a hot water cylinder upstairs. I was thinking of removing the old boiler as I wanted to remove the wall it is on and replace it with a combi boiler in a new position. I was assuming this would be more energy efficient too, but am I wrong?

macman

Any new condensing boiler will be more efficient, yes. But it doesn't have to be a combi.

Canucklehead

ed110220 wrote: »

Why is this? What are the advantages and disadvantages?

I'm in a slightly similar position. My new house has a boiler behind the fireplace downstairs with a hot water cylinder upstairs. I was thinking of removing the old boiler as I wanted to remove the wall it is on and replace it with a combi boiler in a new position. I was assuming this would be more energy efficient too, but am I wrong?

Hi...lots of advice on heating and hot water here. Combis make up the majority of new installations/replacements. We discuss customer's requirements after conducting a site survey and advise accordingly.

Canucklehead

C_Mababejive

ed110220 wrote: »

Why is this? What are the advantages and disadvantages?

I'm in a slightly similar position. My new house has a boiler behind the fireplace downstairs with a hot water cylinder upstairs. I was thinking of removing the old boiler as I wanted to remove the wall it is on and replace it with a combi boiler in a new position. I was assuming this would be more energy efficient too, but am I wrong?

It depends how you measure efficiency.

The combustion efficiency of a modern boiler will be much better than that of your existing boiler,due in no small part to differences burner and heat exchanger technology.

What make and model is your "old" boiler..?

ed110220

C_Mababejive wrote: »

It depends how you measure efficiency.

The combustion efficiency of a modern boiler will be much better than that of your existing boiler,due in no small part to differences burner and heat exchanger technology.

What make and model is your "old" boiler..?

I'm not sure yet, it's hidden behind a particularly hideous hardboard construction above a fireplace, covered in copper foil wallpaper From the age of the decorations I would say it is at least 30 years old, if original, but I'll find out when I open it up.

By efficiency I mean how much gas it will use for a given amount of heating. It uses a hot water cylinder to store the water, which is something I've never had before.

C_Mababejive

ed110220 wrote: »

I'm not sure yet, it's hidden behind a particularly hideous hardboard construction above a fireplace, covered in copper foil wallpaper From the age of the decorations I would say it is at least 30 years old, if original, but I'll find out when I open it up.

By efficiency I mean how much gas it will use for a given amount of heating. It uses a hot water cylinder to store the water, which is something I've never had before.

OK lets break it down....

A modern condensing gas boiler is the current best readily available technology for extracting the maximum amount of heat from a given volume of fuel gas.

The only thing you need to consider is how you want your hot water.


To help you,...just visualise your house as a square box in which you live.

Combi-turn tap on,energy consumption= 30-40Kw...you wait for the nice cold water from the incoming main heating up. As it heats up,you export the unusable water down the drain because it isnt yet hot enough. This is money flowing down the drain. Your flow rate is constrained by certain parameters.You turn tap off.Boiler goes off. Boiler fails? no backup,no hot water...more complex,more expensive to fix. causes excess demands on water and gas networks.


System boiler,-it uses maybe 17Kw. It can do heating and hot water at the same time.You get a full tank of hot water in maybe 30 mins. Any heat loss from the cylinder is exported to the home so not lost. You can lag your cylinder.You have plenty of hot water at good flow rates to all taps. You have an immersion heater as a back up against boiler failure. You are not putting excess strain on the gas and water networks and wasting precious resources. Your shower is not exposed to the vagaries of temperature and flow fluctuations,should someone else run a hot tap elsewhere in the house (as in combi). Boiler is simpler and therefore more reliable and fixable.