you might as well because i suspect its going to take you a long time to make your mind up .
2 Quotes for new heating - what option should I choose - advice appreciated
- Thread starter hztm2008
- Start date
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Thanks for the info - I am more than happy to make an informed decision but it is beyond my capability to decide whether I need a 28kW, 32kW or 37kW boiler - three companies - three different size boilers recommended.
aah yes, but without the fun element, calculations are like reading a playboy magazine and doing at is more fun i tell you! I had some thrills when i did that, and also had a cup of tea afterwards, sat down and was so pleased with my experiment. (saying this of course in jest)
Caculation is fine, as long as the data used as input to the calculation is correct.
Heating water as an when required requires a boiler with a large heat output 27 kW or more. And it is only burning while water is flowing. Heating water before it is needed and storing that heated water in a cylinder does not require 27kW or more. It can be achieved with 10 kW or less but burning for a longer time. Also the cylinder option is far less reliant on there being adequate mains pressure and flow to ensure the 27kW boiler will not shut down due to low pressure, low flow or over heat.
A 10kW boiler is more than enough to heat an average sized house. Some would argue that 10kW would not heat the house quickly from cold. That could be true sp ypu tuen the heating on a bit earlier.
Heating water as an when required requires a boiler with a large heat output 27 kW or more. And it is only burning while water is flowing. Heating water before it is needed and storing that heated water in a cylinder does not require 27kW or more. It can be achieved with 10 kW or less but burning for a longer time. Also the cylinder option is far less reliant on there being adequate mains pressure and flow to ensure the 27kW boiler will not shut down due to low pressure, low flow or over heat.
A 10kW boiler is more than enough to heat an average sized house. Some would argue that 10kW would not heat the house quickly from cold. That could be true sp ypu tuen the heating on a bit earlier.
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Lets us look at basis and simple facts and figures
Cylinder needs on average 24kw
You specify 15 +3kw
It is not middle of winter so let us assume 10 kW will suffice for heating plus your allowance of 3 for HW
You will be short of 11 kW to heat cylinder
It will be like undersized gas carcase when a combi fires and four gas rings are being used in the kitchen
Tony reason you do not want to discuss facts and figures is that you have not thought it through. I respectfully say you are a clever man but basic ideas elude you
For how long does it require 24kW ?
To heat a known volume of water by a known increase in temperature requires a certain number of kW Hours.
A 24kW burner running for 1 hour will have the same effect on that known volume of water as a 12kW burner running for 2 hours.
( heat losses and differences in burner efficiency will alter that very slightly )
Bernard, who says you need to run a cylinder rated at 24kw for one hour. Recovery rate is quoted as cylinder getting to 70% or some such figure in quoted time which is quite small at 12, 15, 17 or some number of minutes. Does the boiler need to supply 24kw for the full duration? No it does not. Does the boiler need to deliver 24 guns when cylinder is cold? Yes it does
I was going to throw a spanner in the works but have deleted what I wrote as I am looking for a response from another forum member as to what his/ her thoughts are on the subject.
I fitted a 300l cylinder for a client along with two Baxi 105e boilers. One boiler was used to heat the cylinder
The client moves into his new house. He has two sons who depleted the cylinder of all the hot water. Father goes in for a shower and there is no hot water. He waits for 10 minutes and has a shower
The point I am making here is that cylinder requires all those horses to get rolling. Skimp on that like some installers do for gas lines, I will grant you, system works, but it working like it should? I have to say no.
By the way, run a SE boiler undersized for heat load, you soon find out what happens to combustion chamber through condensation.
I was going to throw a spanner in the works but have deleted what I wrote as I am looking for a response from another forum member as to what his/ her thoughts are on the subject.
I fitted a 300l cylinder for a client along with two Baxi 105e boilers. One boiler was used to heat the cylinder
The client moves into his new house. He has two sons who depleted the cylinder of all the hot water. Father goes in for a shower and there is no hot water. He waits for 10 minutes and has a shower
The point I am making here is that cylinder requires all those horses to get rolling. Skimp on that like some installers do for gas lines, I will grant you, system works, but it working like it should? I have to say no.
By the way, run a SE boiler undersized for heat load, you soon find out what happens to combustion chamber through condensation.
Fair point mebbe. Ultimately its better to have the horses and not need them all of the time than to have a few and need all of them sometimes?
But is that efficient?
Guy I worked for has one son who stands under the shower until it goes cold. He talked about upgrading his cylinder but then came to the conclusion that no matter what size he fitted his next son in the q would still be showering cold.
But is that efficient?
Guy I worked for has one son who stands under the shower until it goes cold. He talked about upgrading his cylinder but then came to the conclusion that no matter what size he fitted his next son in the q would still be showering cold.
I was using round figures
Then either a larger cylinder or enforce a limit on the time the hot water can be used by a person in the shower.
Flow sensor starts timer, after the allotted time there is a warning bleep. rinse off quick. 20 seonds later a valve closes to shut of the hot flow. Sadistic and it shuts rapidly, instant cold shower, or nice person., it closes slowly so there is a gentle change from hot to cold. Very nice person and it doesn't completely shut off the hot.
Perhaps he saw a programe on TV about cold water shock therapy. I do this now, just for the fun of it, my combi boiler is developing a problem where shower starts off nice and warm, and after a while when I have soaped all over it starts going cold gradually and then becomes completely cold, I know what the problem is but too lazy to fix it, so I allow it to get cold and give me cold water rinse, which apparently is good for you but you have got to be strong enough it take it, and need good lungs to gasp air as your body goes into shock!
search on Cold water therapy, it was televised a few weeks ago, can't remember which channel.
Here is one link http://undergroundhealthreporter.com/health-benefits-of-cold-water-therapy/
(By the way the problem with the boiler is flow sensor diaphragm, but to overcome problem I allow some hot water to run through the bath sink while taking a shower if I don't want it to get cold, that maintains sufficient flow through the boiler, as flow through shower head alone is not enough to sustain boiler, too lazy to fix my own problems, I have a cold water tap in downstairs bathroom which has a stuck washer, and its gone like 6 months and I haven't manged to change that washer)
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D
Doggit
And that's why I tried to get the OP to compare the flow rate of the existing electric shower, and why I said we're getting side tracked.
Hztm, to try and make things simple for you, in my opinion, Option 1 is going to be your best bet. It covers all your needs, takes up the least space, doesn't require and annual check on the unvented cylinder, and will be the cheapest. But there's nothing to stop you getting other people in, and then coming back to us. And if there's 6 of you in the road considering a new boiler, why not get together and negotiate a discount.
Roger, if the cylinder is sized correctly, boiler output adequate for what the cylinder needs, for the time being forgetting you needs to allow additional to heat the rads, no one will run out of hot water as this set up will recover to 70% power within a very short period
Why will the efficiency be compromised if cuffs and collars match
Htzm, an electric shower rated at say 10.5 kW will heat a few thimbles full of water to mix with cold water to then shower you with drizzle
Put in a 24kw combi, it will supply 9.5l of hot water raising incoming cold water temperature by 35 degree C. Last Friday the temperature here was 4 degree C. Let us assume water from the mains at your kitchen sink is at 5 degree C. 5 plus 35 will give you a delivery of 9.5l a minute plus blending cold water making the whole showering experience far far better than an electric shower ( which at this time of the year will be delivering less hot water, hence poorer shower flow from the head)
Put in a 24kw combi, it will supply 9.5l of hot water raising incoming cold water temperature by 35 degree C. Last Friday the temperature here was 4 degree C. Let us assume water from the mains at your kitchen sink is at 5 degree C. 5 plus 35 will give you a delivery of 9.5l a minute plus blending cold water making the whole showering experience far far better than an electric shower ( which at this time of the year will be delivering less hot water, hence poorer shower flow from the head)
Obviously that is a few thimbles full per minute
How many thimble fulls in 9.5 litre ?
10 kW heats a few thimble fulls per minute. ( all the 10 kW of electrical power goes to heat the water at point of delivery )
24 kW will heat 2.4 times a few thimble fulls per minute, a bit more than double speed drizzle ( a bit less as some of the 24 kW is lost in the flue and pipe work )
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The maths gas already been posted.
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