We're about to install a new en-suite bathroom ourselves, but to gain the space to do this we need to lose our hot water tank and re-site the boiler. As the boiler is 15 years old we're happy to replace it and it's been sugggested that we install a condensing combi boiler. But on doing some research I have found lots of differing opinions as to the suitability of a combi boiler. My mum's had one for 16 years and loves it. We live in a 5 bedroomed 3 reception house with one bathroom and a downstairs loo. The bathroom has an electric shower which we would keep. The new ensuite is to have a sink, toilet and shower, to run off of the new boiler. There are just the 2 of us in the house as the kids have (nearly) left home, and we use the shower regularly and the bath very rarely. We also have a washing machine and dishwasher. Please could anyone advise me as to whether a combi boiler would be Ok for us, and advice gratefully received. We are also considering installing a water softener at the same time. Thanks Lynne
- Is the water flow good enough? Check it at the kitchen tap by timing how long it takes to fill a container of known size. If you are getting at least 20 litres per minute, then it should be adequate, although 30 would be better.. If it's only 10-12 then it is not.
- Do you think it's possible that the bathroom shower will be switched over to running from the boiler in the period of time that you expect to stay in the house or that if this is a shortish term that you might want to upgrade the bathroom to perhaps improve saleability? This turns it into a two shower requirement, especially if the house becomes more populated after a sale.
The first of these points is a go/no go for using any form of mains fed hot water, including a combi (although some can be run from a roof tank. and you'd still save the cylinder space). You can potentially get the water service pipe from the road upgraded if the flow is poor, but that depends on what the main there can de and can be costly.
The second point is on sizing. It would make sense to go for a
28-30kW (at least) output boiler to provide adequate capacity in case you do need to account for additional requirements. On the heating side it doesn't matter about possible oversizing because they self adjust (modulate) down to the requirement at any point in time.
As Andy said, the showstopper is if you have insufficent flow of cold water from the mains. Assuming that is OK then your circumstances sound like an ideal match for a combi.
How many radiators out of interest? Is the place well insulated?
Chances are you can probably ignore the heating side of the equation althgether since if you choose a boiler that will give you the hot water performance you want, then it will usually be more than adequate when running the heating.
You ought to make sure your new shower is thermostatically controlled, that way you wont experiance changes in temperature when you are in the shower and the washing machine decides its time to refill.
Go for a high flow combi, if the mains flow is OK.
Vaillant AquaPlus
Alpha CB50
Worcester-Bosch Greenstar 40kW
Cheap condesning boilers available from:
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combi explanation for you....
Firstly, a combi is a "combination" of the heating and water system in one case, eliminating external tanks and cylinders, and generally supply hot water at high main pressure. To confuse a little, some can run at very low pressures and even off tanks. Generally most are fed from the mains. It is generally a matter of mounting the boiler and connect up the pipes. The expert designers have done the hard work for you and put all in one case.
There are three types of combi:
1) The Infinitely Continuous Combi -
Heats cold mains water instantly as it runs through the combi. It never runs out of hot water. This is the most common type of combi, generally having lower flowrates than Nos 2 & 3 below. The largest flow rate instant combi is a two bathroom model, 22 litres/min ECO-Hometec. Being a condenser it is very economical too.
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Unvented Cylinder Combi -
An unvented cylinder is a similar to a conventional cylinder but run off the high-pressure cold mains. A combi with an integral unvented cylinder has approx 60 litre cylinder heated to approx 80C, with a quick recovery coil that takes all the boilers output. A fast acting cylinder thermostat ensures the boiler pumps heat into the cylinder ASAP with a recovery rate from cold around 5-8 mins (Ariston claim 8 mins). The 80C water is blended down to about 45-50C. e.g's, Ariston Genus 27 Plus, Glow Worm, Powermax, Alpha CB50.
The Alpha CB50 is a combination of both having atwo stage flowrate, of high flowrate when using the stored water with an automatic flow regulator switching in to reduce flow to an invinately continuous flowrate of approx
11 litres/min.
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Heat Bank Combi -
Incoming water is instantly heated running through a plate heat exchanger (as is most instantaneous combi's) that takes its heat from a "domestic hot water only" store of water at approx 80C (instantaneous combi's take the heat from a heat-exchanger heater via the burner). A fast acting thermostat ensures the boiler pumps all of its heat into the store ASAP with a recovery rate about 5-8 mins from cold. The 80C water is blended down to about
45-50C. They are generally two stage flow rates, in that when the thermal store is exhausted it reverts to what the bunrer can produce, which is approx 11-12 litre/minute. e.g. Vokera & Worcester floor standing models (standard washing machine sizes).
N.B. The heat bank is a variation of a thermal store, but is "not" a thermal store in the conventional sense in that a coil carrying cold mains water runs though a store of hot water kept at about 80C. Heat-banks are far more efficient and give higher flowrates than conventional coiled thermal stores. The stainless steel plate heat-exchangers do not scale up so easily.
5) Combined Primary Storage Unit (Not classed as a combi, but a derivative of a combi, but still a one box solution, so still in the same family)
These are a combination of a large thermal store, or heat bank, and boiler in one casing. The units are large (larger than standard washing machine size) and floor mounted. The heating is taken off the thermal store, which in many cases the DHW taken off the store using a plate heat-exchanger (heat-bank). Unlike the Heat-bank in 3) above the thermal store supplies heating "and" DHW, giving the "combined" to the title. They are available from 1 to 2.5 bathroom models. Gledhill do an excellent condensing version, the Gulfsream 2000.
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2) 3) 4) & 5) have high flowrates. No. 1 "generally" has low flowrates but there are always exceptions and some can be high - e.g. the ECO-Hometec infinitely continuous combi, actually has a very high flowrate. Nos 2), 3)
4) & 5) use stored water, but in different ways. Unlike No. 1 "some" versions will eventually run cold, but that takes quite a time, hence some are referred to as "two bathroom" models, having the ability to fill two baths with very fast recovery rates. As hot water is being drawn off the high rating burner is also reheating. Very rare do these combi's run out of hot water in average use. When taking one shower the burner may be re-heating faster than what can be drawn-off. No. 3) above uses stored water but will not run out of hot water (high and low flowrates). Most versions of N. 4) above are two stage flowrate models (high and low flowrates) and will also not run out of hot water.
There are combi models that give hot water and heating simultaneously as Combined Primary Storage Units do. Most don't as they are hot water priority.
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