** New Boiler Advice Please **

Some of that is wrong or doesn't apply in the UK.

To decide whether your shower can be supplied by a combi, you need to measure the amount of water coming out of it, and you need to know what pressure it requires.
Measure one with a jug/bucket, and ask your water provider about the other, or measure it with a gauge(£12).

In other words, that's the resistance of the valvery matters, as does the size of the holes in the outlets.

Depends on your present pump too - if it's 4 bar you'll never get the same performance from a combi!

You won't get much saving by using a combi rather than a store. Most of your gas goes to heat the house, normally. Some of the losses from the cylinder do go to heat the house.

NB a CD50 is a storage combi, the flow rate is not exciting at all once the store is used.

ChrisR said:

Some of that is wrong or doesn't apply in the UK.

Click to expand...

Please tell us where it is wrong. Is physics different in the USA? Differnt atmosphere? Gravity different? The Rinnai is a big seller in the USA - sold here.

<snip the rest>

NB a CD50 is a storage combi, the flow rate is not exciting at all once the store is used.

Click to expand...

That takes quite a time to happens as the boiler is reheating as you draw-off. Once exhausted it reverts to around 11 or 12 litres/min. the recovery rate is in few minutes.

Those who have them love them. Don't guess, find out.

Water Systems said:

NB a CD50 is a storage combi, the flow rate is not exciting at all once the store is used.

Click to expand...

That takes quite a time to happens as the boiler is reheating as you draw-off. Once exhausted it reverts to around 11 or 12 litres/min. the recovery rate is in few minutes.

Those who have them love them. Don't guess, find out.

Click to expand...

You are quite right there is a wax stat which turns it down to 10 litre flow rate once store is used so that the temperature of the water doesn't suffer. However as you say, because it is a large store at 50 litres and the boiler is at full power during the use of the store, running out is unlikely when taking a shower, only people with corner baths would suffer, but all that will happen is the speed of filling the bath will slow down.

On the other point, I apreciate you showing me the article which does make some valid points but it is not a research paper and doesn't reference any, so although it is one step closer than a wild guess it is still propaganda..

Water Systems said:

Water heating accounts for 20% or more of an average household's annual energy expenditures. The yearly operating costs for conventional gas or electric storage tank water heaters average $200 or $450 respectively.

...standby losses represent 10% to 20% of a household's annual water heating costs.

Click to expand...

So thats 10% to 20% of $200 (we mostly use gas boilers) = $20-$40 = £10 - £20 a year. On a total energy expenditure of $1000 (£500). I have a feeling that a bit more attention paid to insulation and draughtproofing would make more impact.

Water Systems said:

Life Expectancy

Most tankless models have a life expectancy of more than 20 years. In contrast, storage tank water heaters last 10 to 15 years. Most tankless models have easily replaceable parts that can extend their life by many years more.

Click to expand...

I would have said the reverse was true. A combi that lasts 20 years? And is more economically repairable than a system boiler?

Paul Barker said:

Water Systems said:

NB a CD50 is a storage combi, the flow rate is not exciting at all once the store is used.

Click to expand...

That takes quite a time to happens as the boiler is reheating as you draw-off. Once exhausted it reverts to around 11 or 12 litres/min. The recovery rate is in few minutes.

Those who have them love them. Don't guess, find out.

Click to expand...

You are quite right there is a wax stat which turns it down to 10 litre flow rate once store is used so that the temperature of the water doesn't suffer. However as you say, because it is a large store at 50 litres and the boiler is at full power during the use of the store, running out is unlikely when taking a shower, only people with corner baths would suffer, but all that will happen is the speed of filling the bath will slow down.

Click to expand...

Yep and most of it will be full by the trime it reverts to 11 litres/min. by then you can be in the bath and it can be filling as you are in it. The overall speed of filling a cornder bath is still high as the bulk will be at a high flow rate.

On the other point, I apreciate you showing me the article which does make some valid points but it is not a research paper and doesn't reference any, so although it is one step closer than a wild guess it is still propaganda..

Click to expand...

Don't be ridicuous. You are making yourself to be a fool saying that. It is from the US Dep of Energy (a US government body) - they dare not put out propaganda or they will be roasted. They are down the middle. More info..,. read on...

Bibliography

This list does not cover all available sources of information on tankless water heaters, nor is the mention of any publication, product, service, or organization to be considered a recommendation or endorsement. This list was updated in May 1999.

"Efficiency of Tankless Domestic Water Heaters," Energy Design Update, (7:4) pp. 6-9, April 1988.

Extended Range Tankless Water Heater, J. Harris, Harmony Thermal Co., 1993.
Available from National Technical Information Service (NTIS), 5285 Port Royal Road, Springfield, VA 22161, (800) 553-6847. 33 pp., $19.50, Order Number DE 93013327.

"Going Tankless," P. du Pont, Home Energy, (6:5) pp. 34-37, September/October 1989.

"Instant Hot Water-Maybe," A. Wilson, Journal of Light Construction, (7:2) pp. 55-56, November 1988.

"Never-Ending Hot Water and Energy Savings, Too," R. Layne, Popular Science, (228:4) pp. 106-08, 150-51, April 1986.

"On-Demand Water Heaters," J. Wagner, Journal of Light Construction, (15:4) pp. 51-54, January 1997.

Performance of Instantaneous Gas-Fired Water Heaters, National Bureau of Standards, 1987. Available from NTIS, (see above). 66 pp., $27.00, Report Number PB-87200390.

"Seisco Tankless Electric Water Heater Sets New Standard," N. Nisson, Energy Design Update, (17:5) pp. 14-16, May 1997.

"Tankless Water Heaters," Consumer Reports, (51:1) pp. 53-55, January 1986.

"Targa Energy Unveils New Gas-Fired On-Demand Water Heater," N. Nisson, Energy Design Update, (17:6) pp. 13-15, June 1997.

That will keep you quiet for a while.