Combi boilers

[vicky whitworth]

Hello, I wonder if anyone has any views on oil combi-boilers to heat hot water and a central heating system? Our concerns is...we are installing a cast iron bath and we like lots of very hot water in our bath. Will a combi-boiler be able to heat sufficient water hot enough and quick enough? We had combi-boilers in flats in the 1980s and they were very slow flow to get sufficient hot water. Out plumber tells us they have improved since then. Also when the central heating is running would that impact on the amount of hot water we could get through to the bath? We would prefer to move away from an electric immersion heater, which is what we use at the moment as it needs space for the storage tank but we do know that the immersion gives us plenty of hot water at a fast fill rate.
Any thoughts gratefully welcomed.
Vicky

 

[Edwardia]

My husband used to be CORGI registered years ago and had all the relevant ACoPS when we moved here a few years ago. He installed a combi bolier which he described as the second best boiler on the market and it cost over £1000 with 40% off and it conked out in under 5 yrs. No prob with flow or hotness of water bbut the printed circuit board went and then the valve thingy that switches between water and heating, £200 a time. I'd suggest getting a cheap combi and replacing when it conks out or choosing another type of boiler altogether !

 

[jocelyn plummer]

It most certainly will give you lashings of hot water. 6 years ago we had a big double ended roll top in one of our properties... combi gave as much hot water as it needed.

 

[FamilyWiggs]

Quantity of hot water is not the issue with combi boilers - in a former house it filled our roll-top bath fine.

Flow rate is another issue altogether though - it had probs supplying enough hot water quickly enough for the "victorian" rose power shower.

 

[Flyfisher]

Quantity of hot water with a combi-boiler is, effectively, unlimited; it will keep heating the water for as long as the hot tap is turned on.

However, as FamilyWiggs points out, flow rate may not be adequate for a 'whooshing' shower, which was the deciding factor against a combi for us since we mostly shower. Our decision was also made simpler by the fact that we had a whole new system installed so we could choose a large hot water tank, easily big enough to fill a large bath. Hopefully, this will give us the best of both worlds.

 

[MdB]

Flow rate for a combi boiler is subject two limits. The first is how fast the combi boiler can heat the water. If it is low powered like the one in the caravan I'm in then it is just about good enough for a shower with a small shower head but would take forever to fill a bath. You can get over this problem easily by getting a powerful enough boiler. The second issue is how much water you can get from the mains. If you want to half fill a 300 litre bath in 5 minutes then you need a 30 litre per minute flow rate. You can easily measure your flow rate with bucket and a stop watch from the cold tap in your kitchen. If it isn't good enough for you then I doubt there is much that can be done. I guess a bigger pipe from the main water main would be needed.

 

[michael]

I will be looking to replace one of my two combi boilers in the near future but is there a better, cheaper way of heating your home and supplying hot water other than gas? I just feel that gas will be very vulnerable in the future with regard to supply and price governed to some extent by international politics, so I’m a bit reluctant to spend £1000 on a new boiler and not be able to run it sufficiently in the future. Oil heating also seems to be extremely expensive and vulnerable at the moment. What are the alternatives? Can you get heating and hot water from a purely electrical installation?

 

[Flyfisher]

I think we'd all like to know the answer to those questions!

My view is that gas is the cheapest, most convenient, energy source at present and will be for decades to come. That's not to say it won't be expensive though and I expect it to become even more so, but I can't see oil ever being cheaper. You can certainly power the heating and hot water from electricity but that's no cheaper than gas as far as I can tell - even with new technology such as heat pumps. Probably the cheapest method would be a wood burner but, unless you have free access to lots of wood to burn, it's not cheap to buy logs - and I expect this fuel source will increase in cost quite rapidly as wood burners become ever more popular.

Cheap energy is a thing of the past. The only way to save is to use less.

 

[Horace]

I have had both types. In one house we fitted a combi (one of the best, most powerfull etc etc). It still took forever to fill the bath and our water pressure was very good. The boilers priortise hot water and not heating. Thus if you run a bath on a chilly morning (which takes 20mins) your heating doesn't come on until you stop running the water. That can make for a chilly bathroom first thing!

However, plumbers like them becuase they are easy to fit (no hot water cylinder to find a place for or tank in the loft).

I now have a normal system boiler which does the heating and heats a pressurised hot water tank (megaflo but there are other makes). This has the advantages of doing away with the loft tank and provides gallons of hot water at high pressure. However, you need to make sure that you have sufficient mains water pressure for it to work properly.

Personally, I find the argument that combis are efficient becuase they only heat the water you need a bit spurious. In my experience the boiler fires when you open a tap, it runs for ages until it gets hot and then you waste all the hot water in the pipes once the tap is turned off. The pressurised tanks are so well insulated that I could get hot water 3 days after the boiler had been turned off.

 

[GeoffP]

I had doubts when I had a new combi fitted some months ago but even with the thermo turned down, there's plenty of hot water. The flow rate on mine doesn't seem to be any slower than normal tap pressure but is obviously slower when using H & C taps at the same time as there's only one pressure rather than two with the tank system.


On a different tack, has anyone looked into hydrogen power?

http://kww.autobloggreen.com/2007/09/07/itm-power-is-back-with-more-home-hydrogen-promises/

I've not delved further into this company as, if they are actually available, the systems shown would appear to be ludicrously expensive but I have seen a video of hydrogen being used to fuel a blowlamp so surely it could also be used to fuel a boiler and the production seems to be reasonably cheap.

The emphasis on other sites appears to be directed at running your car on hydrogen rather than domestic uses. Loads of videos on YouTube

Dreaming again?

Geoff

 

[AMc]

Mains gas remains the cheapest and most efficient way to heat your home. Oil is more expensive and the price varies dramatically - I'm paying more than 50% more for this seasons delivery than the one 2 years ago. LPG is similarly expensive.
Electric storage heaters are an option, but I hate them as IMHO the house is hot in the morning and freezing last thing at night.
Wood can work out better if you have a ready cheap supply but the pellet systems are expensive and the log burning boilers are labour intensive.

We're eventually fitting an Air Source heating which we're promised will work out cheaper than oil but the capital cost is substantially higher (£12K vs £2K for us).

If you have access to mains gas I think that is going to be your lowest cost option in terms of installation and running for a little while yet.

 

[MdB]

Electric storage heaters are an option, but I hate them as IMHO the house is hot in the morning and freezing last thing at night.

Economy 10 rather than Economy 7, improves electric storage heaters considerably as it gives you cheap electricity from 1pm to 4pm and 8pm to 10pm as well as 12am to 5am. (I still hate them too though)

We're eventually fitting an Air Source heating which we're promised will work out cheaper than oil but the capital cost is substantially higher (£12K vs £2K for us).

Our ground source heat pump and underfloor pipework will cost about £5k all in though this doesn't include installation which we are doing ourselves (underfloor pipe work went in today ). Oil would have cost around £4k if again we did as much of the install as possible.

 

[Flyfisher]

The advantage of hydrogen is that it burns cleanly and the result is water (vapour). However, I believe it has a relatively low calorific value, so you need a lot of it, which gives rise to storage issues leading to very high pressure tanks = needs to be very strong = tends to be very heavy. There's also the issue of generation. Electrolysis of water needs lots of electricity.

I'm sure one of these new technologies will eventually come good but, like most new technologies, the early stages are characterised by high costs and teething problems and the early adopters pay the price. But continued R&D generally works wonders, volumes gradually increase and prices plummet. I'm assuming (hoping) that my new gas boiler will last 10 years by which time there will hopefully be an obviously better technology to replace it with.

 

[MdB]

Hydrogen is extracted from natural gas and as such will never be cheaper than gas to run.

 

[GeoffP]

MdB I didn’t know that. I thought it was made by electrolysis although I understand that the old “Town Gas” as stored in the gasometers contained a high proportion of Hydrogen.

 

[MdB]

Hydrogen produced by electrolysis is costs a lot more so it isn't done currently on an industrial scale. In this mode, you can think of hydrogen being purely an energy storage mechanism and not a fuel in its own right. You will of course get far less energy out then was put in to make it in the first place.

When the oil / gas runs out and we move to getting our energy from renewables and nuclear, hydrogen might have its uses as an energy storage facility for cars but otherwise I can't see it being used, there isn't any point.

 

[Penners]

has anyone looked into hydrogen power?

Cue Biff's 'hydrogen is not a fuel' explanation.

*Edit* MdB beat him to it.