Which Boiler Advice

[AndyHingston]

Hi All,

Just stumbled across this site and read some really useful threads.

I am in the middle of considering which type of boiler to choose fo our 4 bed bungalow.

Existing System - Ideal Elan, cylinder in loft only used for DHW. Heating is via Economy 7...not good !!

At our previous property we comissioned British Gas to install Worcester 28CDi Combi, which we were very happy with, although the dro in hot water flow rate did take some getting used to! As I need to fi this system myself, I believe that a Combi is the best choice due to m limited knowledge of heating systems, although a Mechanical Engineer b trade.

The flow rate has been a major decision in my replacement boiler choic and at first I was considering a boiler with an internal store to ge around the long delay in hot water reaching the tap and an increase flow rate.

After careful consideration I was opting for the Baxi Combi Maxflow W which has a 54lt store and can deliver 16lt/min until the store ha depleted. However, I guess this flowrate then drops whilst the stor is replenished and I have been unable to locate the flowrate.

Further investigation revealed that the high end Condensing Boilers ar offering 16lt/min delivery all the time (at the standard 35 degree tem rise) and in particular the Baxi 133HE Plus Condensing Combi Boile looks a good choice and will give me a far more efficient system.

I guess this choice will not solve the initial delay in receiving ho water?

Some of the threads have indicated that there is specialist equipmen required for fitting condensing boilers, is this true?

Any help would be greatly appreciated in helping me choose the correc system.

Regards

And

-- AndyHingston

[Paul Barker]

I prefer the Worcester Greenstar 440 for a storage combi, because i has the thermal store. Worcester and baxi took the opposite approaches The thermal store is more likely to keep up with demand.

Also consider for excellent value for money the Buderus 600 28c. N real storage but a small amount. I fit one of these and can't wait t sell another they are perfect machines. If you are an engineer, trus me this is an engineer's boiler. Bosch now own Buderus and Worceste won't allow them to quote the true flow rate of this boiler (13.1 lt at 35 degrees). The other boiler I was fitting a lot of is the Bax

105e, the hot water on the buderus is far superior, it is rigth ther straight away and it never fades, this is quite uncharacteristic o combis. I have a hot water cylinder and advocate that system, but if wanted to do away with it, I would be perfectly happy with the Buderus It's a large beast, marvelously engineered and constructed. They als now do a wireles programable/thermostat with eco features for only 5 something pounds.

Only one gripe about the Buderus, you have to set up the gas and ai mixture, for which you need a very sensetive manometer. A U guage won' do. However, on the one I fitted this was c*ck on. The Worcester boiler of this type don't require the installer to set them up. I think Buderu is just covering themselves, in all likelyhood it's set up fine in th factory. I know installers who don't have the right equipment, the just fill in the sort of figures the manufacturer is looking to se (she don't tell anyone that's going on).

I hope that helps.

If you can afford it, get S plan controls and a new fast recover cylinder and a condensing system boiler. If you are poor get a Buderu

600 28c.

Pau

-- Paul Barker

[Andy Hall]

It will drop to a disappointing 11.4lpm for 35 degree temperature rise.

of the above assumes that the mains water supply is adequate.

I guess it depends what you mean by efficient.

It may be for some.

- Some are factory preset

- Some are checked by reading the meter and checking the gas flow rate

- Some are set simply using the traditional gas valve control and a manometer

- Some require a combustion analyser costing around £200-250. You may be able to rent or get a CORGI fitter to come and do it for you. Check with manufacturer for recommendations. Not all fitters have one, believe it or not.

If you're looking for mains pressure water at respectable volume, considering that you already have a cylinder in the loft, why not swap it for a heat bank. This would give you hot water at a rate that will most likely be limited by what the main can do. Water is stored at 80 degrees, so in effect you get a third more energy storage for a given volume of cylinder than at the traditional 60 degree HW cylinder. The water in the cylinder is made to be either part of the primary heating circuit, or if the latter is sealed, it is normal to use an indirect arrangement where the water in the cylinder is a vented tertiary piece. The header facility for it can be incorporated in the cylinder. The principle is that a stainless steel plate heat exchanger is used with water to be heated and used on the one side, and the bulk cylinder water on the other is pumped through. There is a sandwich of alternating plates which provides a large area between the two lots of water so heat transfer is very high (100-200kW). Using a flow switch on the potable water side, the secondary pump is started when you turn on a tap.

Heatbanks have the advantage that you can select as you like, choosing a system boiler to run them, or alternatively a modest combi in the kitchen if you'd like quicker hot water there with the heatbank run from the heating circuit. The other point is that you can install a heatbank yourself because there is no volume of water under pressure as there would be with a pressurised cylinder. Professional installation is required by the Building Regulations for these.

[IMM]

Very wise. A combi is very easy to install for DIY/limited kniowedge.

The Worcester Bosch Greenstar 40Kw combi delivers 16 litres/min and never tails off.

Look at

I guess this choice will not solve

For no lag and 18 litre/min flowrates also see the Alpha CD50 condensing storage combi:

"The Alpha CD50 condensing storage combi is designed to satisfy the hot water and heating requirements of the larger home whilst reducing energy consumption. When the store is fully charged an equivalent domestic hot water output of 50kW gives a flow rate of up to 18 litres per minute at approx 55C - 60C, enough to fill an average bath in about 3 to 5 minutes."

[Andy Hall]

There is marketing-speak in this:

- The specification doesn't say what an average bath is.

- The maximum output rate to hot water is 32kW implying max of 13lpm once the small store runs out.

[IMM]

The avergage bath is now 80-100 litres. This will fill an avarage bath in minutes and never run out of hot water at any time. 3 minutes to recover the water store.

It is a condenser, so more towards 14 litres/min.

[Jim Alexander]

Suggest checking the adequacy of the existing gas pipework if you are thinking if a large combi. You might be surprised how short a run is OK with 22mm. Its possible you might need to upgrade to 28mm.

Jim A

[Andy Hall]

Really? Have you measured one lately? That volume is a paltry amount in the bottom of a standard sized bath. If it seems like a lot to you then perhaps Archimedes principle could be at work?

It wouldn't be adequate for any female I know.......

This is the marketing claim. They neatly sidestep any obvious references to wat the rate is when the small store runs out.

Which is a separate issue and again presenting something in the most favourable light rather than the reality of what happens when the small store empties. They aren't even honest enough to give the figures because they are embarassing.

It being a condensing boiler or not is irrelevant to this. The heat output to water heating determines the flow rate at the specified temperature rise. Whether or not it's a condensing boiler only impacts how much energy is going in for that.

You have to dig beyond the marketing hype and look at the hard numbers to determine what is really going on.

As soon as I see a manufacturer obfuscating data like this and just presenting a rosy view, my thought is what else are they obfuscating and I look elsewhere.

[Markus Splenius]

Really? I have the misfortune of knowing one 150 litre female! :-)

32 kw, 3 minutes would imply the store is 39 litres if we assume a 35 degree rise. Is it?

M.

[Roger]

The message from "IMM" contains these words:

Yet more evidence of dIMMs complete lack of numeracy.

80 to 100 is not an average, it is a range with a mid figure of 90.

We established a bit ago that dIMM doesn't clean his teeth in his bathroom. Now it appears he doesn't bath either. E&OE a rough calculation suggested that 80l in a bath would produce the level of water that the water misers of WW2 might have approved of and (in my bath at least) 100l would produce a depth before immersion of about 6". My usual bath would take at least 120l, well above the extreme of dIMMs range. The alternative of course is that dIMM is so fat that he doesn't need much water in his bath in order to raise tide level to the overflow. :-)

18l per min. for 3 to 5 minutes is 54 to 90 litres which is not far away from dIMMs range but it would appear he has forgotten that 55 - 60C would make for a very painful bath. Diluting 90l of 60C water with 60l of 10C water would give 150l of 40C water and a brim full bath.

dIMM of course will be true to type and merely dismiss this as more 'drivel' thus yet again displaying to the ng his complete absence of any meaningful cogitative ability.

[IMM]

I repeat: "The avergage bath is now 80-100 litres." They are shaped to hold less water.

An actual claim. I have see the CB50 in acvtion, very impressive. A poster here as one and confirms that.

The small cb50 was about 11.5 l/min. This should be over 13 l/min. Not bad at all. Rarely will you need to drop to the lower stage in an average home.

3 mins at 70% exhausted., proba bout 5 from cold.

Condensers provide more heat for the input. This and the B-W 440 should be more than ideal for the original poster. The 440 can go just about anywhere with a flexible fluing arrangement and a condensate pump.

[IMM]

If 28mm, only for part of the run.

[IMM]

< snip drivel >

[Roger]

The message from "IMM" contains these words:

As predicted.

dIMM really hasn't a clue when it comes to either facts or figures. The only thing he is even moderately good at is copying and pasting 2nd hand comment but even then the chances are that it will be irrelevant.

[IMM]

< snip drivel >

[Grunff]

The average 'tin tub in front of fire' you mean?

Our bath is 270 litres capacity to overflow. SWMBO fills it to the overflow. Discounting her volume, which can't be more than say 60 litres, that's 210 litres of water. Ours in not a particularly large bath.

[IMM]

It is by modern standards. Get new bath and get your water and heating bills down.

[Grunff]

We only put this one in last summer!

[Bob Mannix]

I did some quick rough calculations and came up with a figure of roughly

10mm depth for 10 litres (8-11 litres depending on the bath). This makes ~270mm depth to overflow for G's bath, which seems about right. 80-120litres would be ~80-120mm deep (before you get in). I would normally run a bath to, say, 200mm deep and it would then reach the overflow when I got in (making me about 70litres (middle age spread)). I would agree that ~200litres was required for a "good" bath, 150litres if you are in a hurry.

Of course, one has to take into account the hot water temperature as you can run cold at the same time as the hot is flowing, which boosts the overall fill rate. Say 30%cold 70% hot, that's 140litres hot for a "good" bath. at

18l/min that would be 7-8min.

All rough figures of course and YMMV, but 7-8min is a long time to wait, unless you go off and do something else (but liveable with I suppose). Emprical observations (from no combi at home (3-4min) and using decent combi away on holiday) would seem to confirm these figures.

[IMM]

Bad move.