To combi, or not to combi..?

[Ouch77]

So after assessing how I can get the gas into the house, and how much hassle the boiler installation will be, the next question I have to ponder is what type of boiler to install.

The current heat source is a coal fire with back-boiler, there's a traditional copper cylinder (with the standard issue, badly fitting, red quilted jacket) in the airing cupboard and 2 black plastic water tanks in the loft above it.

(Judging by a patch of non-matching render on the gable end, I'd guess that one of the tanks was recently replaced.)

From all this I'd assume the heating and hotwater is conventional gravity fed, with a circulating pump by the cylinder.

After the hassle and expense of installing the boiler in the 'perfect' spot, an easy win would be to hook it up to the conventional heating system using the existing F&R pipework from the cylinder to the decomissioned coal-fire which isn't that far away.

However for a 3bed semi, with single bathroom, I suspect a combi may be more efficient (though I've no idea if the mains water pressure is adequate). Is there an easy way to make guesses to the efficiency (or running cost) of a combi against a stored hot water system?

I kinda need find justification the additional cost of a modern cylinder, against 100quid extra for a combi, and getting rid of the cylinder and all the black plastic in the loft. With the price of copper I'd probably get the money back on selling the cylinder to the scrappies.

There's an part of me that also wants a proper power shower, that I doubt a combi could supply, though I can't use that as justification on it's own

There's also the eco factor, of possibly including (at a later date) solar water heater panels on the roof (we have an ESE/WNW aspect, so possibly not that great). I understand this would require a dual coil, indirect cylinder, and would be totally incompatible with a combi setup.

Given the potential cost of the eco-upgrade, would it make financial sense over a 10year plan (about the lifespan of the hardware I'd guess)?

Sorry for the rambling, kinda looking for a bit of a steer here..

 

[linkyplumb]

The very first thing that you need to be looking at, is the incoming cold mains pressure and flow.You will be wasting your money on a combi if you have **** poor flow and pressure.Do a quick check for flow by timing how long it takes to fill say a 10 litre bucket etc.
Obviously this needs to be done from a source directly off of the main, ie kitchen tap or outside tap.

Hope this helps

Graham

 

[ianniann]

Woho, lots of questions!

Not a huge difference in efficiency. I wouldn't panic either way.

Filling a bucket will measure the flow rate but equally important (more important!) is your mains pressure and this isn't simple to measure yourself. Usually fine, most people would know if they have low mains pressure.

Combis provide a good shower, up to a very good shower with more powerful ones, but very few can match the flow rate of a good power shower. Better than some cheap power showers though. It wouldn't usually be worth the expense of trying to achieve power shower levels with a combi in a small house, unless perhaps you are likely to need two or three long showers one after another. A combi will provide hot water continuously forever, while a cylinder will eventually empty.

There are combis that are compatible with solar, in the sense that they can accept incoming hot water. Most can't though.