Of those options, it is only Option 4 that is a 'combi system', the other three use a conventional boiler, with storage tank & hot water cylinder. Combi just means no separate hot water cylinder, the boiler itself heats the domestic hot water.
Correct. Options 1-3 are not combi anyway.There are a couple of things to check and some possibly hidden issues.
Water supply. Measure at the kitchen cold tap the water flow rate. This can be done by timing how long it takes to fill a container of known size and calculating from there. As long as you are getting
25-30 litres per minute or better then it should be OK. Less than that may mean an upgrade to the water main to the street.
Gas supply. This will need to be adequate for the boiler. Normally, this means 22mm pipe to the boiler.
You would have had to do both of these to implement the multipoint anyway.
It may be necessary to run a water supply pipe in 22mm from the rising main in the kitchen to the boiler position to get an adequate flow to the hot taps. Often, systems with roof tanks will have been plumbed in 15mm from the main and this may not be enough.
On boiler sizing, don't go for the bottom end 11 litres/min models. The results will be quite disappointing in comparison to the flow from a cylinder type system. Really, the more the better.... From the heating perspective, the boiler adjusts down anyway.
On Sat, 10 Apr 2004 10:50:02 +0000 (UTC), in uk.d-i-y "Arthur" strung together this:
I'm confused, or you are, one of us is. The above options are not using combi boilers, if you want a combi ignore options 1-3. Are you sure you're clear about what you want, as you don't appear to have grasped what the options are?
If you're selling it, possibly not. You might be lucky and have a punter who doesn't notice, or you might get someone like me who would want the surveyor to test it and if found wanting, factor into the price. I'm picky, though.
Try it out.
Go to the bath tap and using your measuring bucket and stop watch, measure the flow and then adjust so that you get 11 lpm
Bear in mind that in the winter, when the cold mains is around 5-7 degrees, the output water temperature at this flow rate will be 40 degrees - shower temperature. For hot water as you get from your cylinder now (60 degrees), you will have to turn the tap down to about two thirds of this rate. You might dilute it to achieve 50 degrees for washing up, perhaps but you get the idea.
If you feel that this is all OK, then fair enough. Otherwise go larger. Remember that for hot water it is really the flow rate of hot water that matters. Hence it depends on how quickly you want the bath filled, whether there is a shower as well, whether you will run the kitchen hot tap at the same time as other things and so on.
From the heating perspective, having the boiler oversized is not important because it will reduce its power output to match what is needed.
I've just fitted a Worster Bosch Greenstar HE 30... long winded (and incomplete) name for a new condensing combi. It gives out 11+ l/min and gives a wicked shower. The bath and sink takes a minute or so longer to fill up, but it's not forever. That's no hardship when you know that there is no tank that is going to run out.
On Sat, 10 Apr 2004 13:46:17 +0000 (UTC), in uk.d-i-y "Arthur" strung together this:
Ooh, that's borderline trolling territory!
got a Greenstar 35HE and it works a treat. Showers are powerful and waters hot. Obviously it does depend on your water pressure\flowrate and some proper piping to the shower from the boiler. Reliabilitywise Worcester are one of the better at making good quality boilers. Having never actually fitted any of the others I wouldn't like to comment too much. Worcester and Ideal are good, Glow-Worm and Potterton aren't.
Personally, I'd disagree with your inclusion of Glow Worm in those that aren't. I'm also still to be convinced that Ideal made a good choice in using Aluminium heat exchangers in contact with acidic condensate. My opinion would be to put Glow Worm and Worcester in the good
On Sun, 11 Apr 2004 21:12:21 +0000 (UTC), in uk.d-i-y "John" strung together this:
I knew it was a bad idea replying to that post! I nearly stuck at just saying Worcester are good but thought I'd offer my (limited) knowledge\opinions. I'm open to persuasion to the merit of other brands!
With combi's the most important figure is the flowrate. 11 litres/min is fine for showes and the odd slow filling bath. Here is a recent post of mine...
For an even better flow rate and cheap too for what you get, assess using two Worcester-Bosch Junior combi's.
For high flowrates it is cost effective to use two Juniors and combine the DHW outlets. Worcester-Bosch will supply a drawing on how to do it, or ask me here. Two Juniors are available for around £1000 to £1100 depending on what sized units you buy. They have 24 and 28 kW models, you could use two
24kW or two 28 kW combi's or one of each. That is cheaper than the Worcester HighFlow 18 litres/min floor mounted combi and can deliver about
21.5 litres/min and never run out of hot water. The highest flowrates of any infinitely continuous combi is 22 litres/min, which is the ECO-Hometec which costs near £2K.
Have one combi do the downstairs heating on its own programmer/timer (Honeywell CM67 or equiv) and one do upstairs. Natural zoning, so you don't have to heat upstairs when you are not up there saving fuel. The running cost will be approx the same as a condensing boiler heating the whole house. No external zone valves either, and simple wiring up too. The Juniors are simple and don't even have internal 3-way valves.
Also if one goes down you will have another combi to give some heat in the house and DHW too. Combine the outlets for the DHW bath pipes and all the baths you want very quickly and no waiting. Best have the showers on separate combi's. It will do two showers no problem at all.
The Juniors are not condensing combi's, yet overall heating costs will be equivalent to a one condensing boiler as the upstairs will not be heated most of the time.
A win, win, situation.
Its advantages are:
- space saving (releases an airing cupboard). Both can go in the loft, or at the back of the existing airing cupboard.
- never without heat in the house,
- high flowrates (will do two showers and fill a bath in few minutes,
- No waiting for a cylinder to re-heat
- Natural zoning, one does upstairs and one does down
- hardly any electrical control work (running a wire to a programmers/stat and power to each,
- simple no brainer installation,
- minimal components used.
- less piping used
- cheap to run overall as upstairs would be off most of the time
But if a 'normal' boiler is 'on line', there's no reason why a tank would run out either, given normal requirements. And if you want two large baths one after the other, a half decent one with a fast recovery cylinder will have re-heated the cylinder by the time you've had your bath anyway.
Yes, but reputations, bad or good, live on to haunt the manufacturer e.g. Skoda cars are not to bad now but I wouldn't have one although my GP is happy with his...
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