I am about to install a new combi system in a four-bed house - don't lecture me on tanks please - but I am unsure about combi capacity. Is bigger flow always better, equalling buying the most expensive boiler I can afford basically? For this little excercise, capital cost for the boiler shall not be important, I am interested in the priniciple rather the practical.
Fred
Remember to get the full advantage of a large boiler, you might have to upgrade both water and gas mains. And for good flow to more than one outlet at the same time, internal pipework as well.
In this case, bigger is better.
Combi boilers are specified in terms of the rate of flow that they can achieve for a given temperature rise - usually 35 degrees, but do check specs.
In the winter time, this figure will equate to the maximum flow for a shower or for filling a bath. Considering that a bath needs 100 litrres for little more than a splash in the bottom or 150litres plus for a reasonable one, then a typical 13lpm combi will take 10 - 15 minutes to fill it at 40 degrees. You need to decide whether you are OK with this.
There are domestic combis with flow rates of 22lpm, which is obviously a lot better, but these are not at the cheap end of the scale.
For almost all with any significant power level, an upgrade to 22mm or above of the gas pipe from the meter to the appliance is needed if it hasn't been done already.
.andy
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In message , Andy Hall writes
We have an average mid sized combi, 100,000 btu DHW heating capacity - about 15 l/m or so max (for decent water temp) IIRC, we are happy with this, but I certainly wouldn't suggest going for anything smaller. We are a shower family -except 3 yr old daughter so bath filling isn't an issue. Bigger would be better, but depending on your requirements not necessarily worth it.
Yep, ours needed 22mm up to I think 3m of boiler, According to my plumber neighbour some larger ones require 28mm
Look at IMMs recent overview of combis, he is the expert on this group for this sort of stuff. His post is excellent. I just did a Google search on "Combined Primary Storage Unit" and it came up. The higher rate of water flow is the figure you should be going for. The higher the better. IMM did suggest installing "two" Worcester Bosch Junior combi boilers for two bathroom houses with one doing the heating for upstairs and one for downstairs, zoning the house off. I like this idea. I think he suggested combining the hot water outlet to give a higher rate of water flow using check valves. This was a cheap way of having higher rates of flow as two of these boilers is not expensive. Do a Google on "Junior" and that may bring it up. I noticed that B&Q do the Biasi combi boilers for around £390. Having two of these gives around 21 litres of water flow for less than £800. Not bad at all. If you are fitting yourself, a combi is a doddle. Cylinders and tanks can be difficult and very time consuming to install if you want to do a professional looking job.
While you're entitled to your view, there are far more authoritative sources available on here than IMM. People who actually install and use these things in anger - not just quote makers' best scenario claims as IMM does, while never giving the downside.
I'm not an expert in heating, but a fair expert in sorting out the wheat from the chaff in reading newsgroups. And IMM is mainly chaff.
Assuming you're not a pro, or 'doing up' a house to sell, installing a central heating and hot water system in your own house is probably the biggest single expense you'll have. And most with any sense will take the care to find out the very best possible system for their needs regardless of whether it can be thrown in quickly or needs some thought and care in installing. Because a decent system will have a very long satisfactory life. A poorly installed under specced one will annoy from day one.
As regards making a tidy job of pipework, I learned how to do it - largely self taught. It's not particularly difficult in terms of the things many DIY - and indeed needs little in the way of expensive tools.
In message , timegoesby writes
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
I have a hard time to beat the Worcester Bosch 40 Greenstar with a flow rate of 16l/min. Baxi, Vaillant and the lot do not seem to match even this. Where can I find bigger flow rated boilers then?
That seems to be the right choice anyhow. Too bad that in my case that is going to be necessary. At least that is what the plumber said and he seems trustworthy. Speaking of trustworthy, how do you gauge a plumber? I go by gut feeling and things like this: warnings that the pipe needs upgrading and so on, and what are the implications of a condensing boiler yadayada. I am not savvy enough to ask him much more. As long as he can beat a British Gas quote, I am usually not concerned about money too much anymore. Is that about right?
Fred
In message , "Dave Plowman (News)" writes
When it's not cha cha chaf
Sold badged in the UK by Eco Hometec and MHS Boilers. The EC38 will deliver 46kW to hot water and give 22lpm.
Viessmann
Ask for references? Get competitive quotes. Obviously check CORGI registration.
It is easy to beat a BG quote. I could do that, pay for CORGI membership and insurance and still be under a BG price.
.andy
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Or Tango Oscar Sierra Sierra
.andy
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Thank you. That is all I need to know. The most authoritative person in this group on heating and water systems is by a mile IMM. Any half intelligent person can see that. Please take your ridiculous prejudices elsewhere, I don't want to know.
Good advice, and I do consider all alternatives that is why I occasionally look into this group and Google on it. I have fitted tanks and cylinders and they are a time consuming pain to fit with pipes all over the show. A good combi is cheaper to fit with far less hassle and gives the same, if not better, performance. I previously took IMMs advice and fitted a combi with the water section supplying only the showers. The CH side, besides heating the radiators, heated a very large combination cylinder to fill two baths quickly and it worked very well. Doing it again I would consider one very large combi or two smaller combi boilers. Two smaller combi boilers is cheap and quick to install, and far less hassle than tanks and cylinders. I have also been looking into heat banks and no matter how I assess, one large or two small combi boilers comes out the best option all around for me.
good night.
*******************
From: timegoesby Subject: Re: Combi fans: is bigger better Date: Mon, 13 Sep 2004 02:30 Newsgroups: uk.d-i-y
***********Please make up your mind.
You should remember that a standard heat bank is good for around 40lpm (at
60C). This is equivalent to 63lpm in combi delta Ts. That would require 5 cheap instantaneous combi boilers and a commercial gas supply to run them. It is required if you wish to fill a bath in 2 minutes, which, for me, is an essential characteristic.Christian.
That is all you need to know!!!! Don't take advice from people who think they know but know very little at all. That can be very dangerous.
That is nearly true. But most people don't need a commercial setup. Most people are content on a bath fill of 5 minutes and a excellent showers. A combi, or combi's, can do that with less hassle in installation and lower cost .
Depensing on how a boiler is conected to a heat bank (dirrect with a blending valve is the best) you will run out of hot water. Two small combi's will never. The teenagers can stay in the shower all day. Flowrates are important up to a point, but you have to look at the big picture.
In most homes that would lead to floods.
Maxie,nice one. Nice to see you are in good spirits. Good for your soul.
The Greenstar is a v good boiler, with a good flowrate and well priced too.
The thing to do is know your specification and ask them to quote on it. The Greenstar is a god choice, so go for that, do not be persuaded otherwise. It does require a 28mm gas supply, but can be reduced to 22mm towards the boiler depending on the run. Tell him that you checked wityh the maer on the gas pipe size. Some cowboys would keep, or fit, 22mm.
Go on recommendations and ask them to quote. Combi's are easy to fit, even for a dumb plumber, so not that much to go wrong.
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