Which combi for house with 2 showers...

[Dean Lawrence]

Which combi boiler will provide for simoultaneous running of central heating, 2 HOT showers and a good pressure (or flow-rate or whatever), dishwasher (cold feed) and washing machine (hot and cold feed).

This is not really extreme as it will be found in our house in just a few years time as the kids stop having baths and start having showers. The dishwasher goes on in the early evening, as does the washing machine.

Obviously it is difficult to subjectivly define good pressure (or flow-rate or whatever), but I know it when I see it, and I would like to see it it the above setup! Again, hot is a subjective term, but put it this way, I want to have to add cold to stop it from being uncomfortably hot when showering.

Oh yes, it the showers will also not fluctuate, deviate or perform any other kind of -ate, when the dishwasher starts rinsing, or the washing machine starts taking in more water. Or somebody turns on a tap.

Now, which combi boiler(s) will do all that.

Cheers, Dean.

PS, if it had a tap on the side to vend lovely hot tea morning noon and night, that would clinch the deal!

[rob]

other appliances calling for hot water. some will even shut off supply altogether if the shower is the last on its travels. I personally would keep one of the showers electric, you will be glad , if the boiler packs in,at least you will have one way to keep clean . rob

[IMM]

If you want avaege flowrate showers of approx 7 litres/min then the Glow Worm 30kW condesning combi will do fine at approx 16 litres/min. If you have high flow rate showers then you are talking big bucks, with the ECO-Hometec and Mikrofill boilers having flowrates of 22 litres min.

Not applicable.

keep it off when people have showers. This doesn't require a high flowrate, so it is good practice to have an in-line isolator and turn the hot flow right down.

Most people want the high pressure against their skin. 7 -8 litres/min is fine.

You get shower mixer with built-in pressure balancing valves. Or have a thermostatic mixer valve and a separate pressure balancing valve before.

Try the GlowWorm 30kW condensing combi. look at:

[IMM]

You can always have a small in-line instant electric heater in the combi hot draw-off for this. Gives a trickle shower but heats you clean and supplies one tap at a time, so do two.

[rob]

for the shower.

why not look at thermal stored hot water. try Megaflow. This is hot stored water at mains pressure, should give you all you need. Buy a big enough cylinder and you should never run out of hot water rob

[IMM]

One point of a combi is to save space. Megaflows take up space. Also a heat bank is better than a Megaflow.

[John Rumm]

30kW is not going to give 16 l/min... 12 l/m tops assuming you only want the 35 degree temperature rise that they usually quote flow rates at. Worst case (i.e. winter with ground water coming in at say 5 deg, and hot water temp set at 55 - which will allow for a bit of thermostatic mixing at the shower) a 30kw boiler would probably only do about 8 l/min total - or about the same as two top end electric showers.

A high efficiency 35kW combi (or better) may just about do what you want

- but you will need to ensure that if two people are showing there is no one going to turn a tap on elsewhere!

Very applicable if you don't want to be boiled when it decides to fill! This will be more of an issue if you don't have a good flow rate from your rising main.

You could apply the flow restriction trick to the dishwasher as well to limit its impact.

Look for 35kW or better I would suggest.

[IMM]

typo. Here it is:

Glow-Worm 38CXi Condensing Combi Boiler

. BTU's - 130,300 . kW - 38.2

. DHW Flow Rate - 15.5 L Per Min @ 35°C

. Height - 715mm . Width - 450mm . Depth - 334mm

. Sedbuk Rating A - 90.6%

. Built In Frost Protection

. Fully Modulating

PRICE INCLUDES DELVIERY

£934.13 Including VAT at 17.5%

Pressure balance valves will sort that out.

Good point.

[Ben Mack]

In article , IMM writes

Or a Vailant Aquaplus - has a small heat store to ride those surges, and does 170l dhw in 10 minutes, for about the same price. Not condensing, though.

Cheers

[John Rumm]

Yup that sounds more like it.... I was tempted to go for this one myself

but the snag is it won't fit the gap I have earmarked for it :-(

[IMM]

Older technology.

[David Moodie]

A good time for this to crop up.

I am currently considering a similar set up to the OP and the Glow Worm

38Cxi is on my list of combi boilers, along with valliant ecomax 835/2E 14.3L/min.

It now looks like I will go for a condensing boiler although the valliant turbomax plus837E 15.1L/min and Worcester 35CDi @ 14L/min, have also been considered.

The driving force behind these options is a relatively high flow rate (>14L/min at del T =35K), and a condensing boiler looks optimal as I now intend to put UFH in the extension that is currently being planned. The complete central heating system will also be replaced so radiator sizes may also be changed where appropriate

As I understand it one of the key issues regarding the reliability of condensing boilers is the burner and condensate trap design. I would be interested to hear any opinions regarding these two boilers concerning this or any other issues wrt long term reliability. Of course any other boiler recommendations with similar specs would also be of interest.

cheers

David

[Christian McArdle]

One thing to watch out for with high flow rate combis is that they often can't modulate very low on the central heating side. I don't know specifically for the Glowworm. However, some makes of 35kW+ boiler can't even go below 12kW, which in my case is about 50% above the worst case heat loss for the house and would lead to really quite excessive cycling.

Christian.

[IMM]

The Glow Worm is a good boiler design, and I think made in, Holland. Glow Worm are now part of the Vaillant group. The heat exchanger is stainless stell and of a v good design. the boioer is well priced, well spcced, highly efficient with a decent flow rate.

Alternately, you could use two cheaper non-condensing combi's for the same price, or less. One does upstairs heating, one downstairs, giving natural zoning, with a CM67 timer/stat on each. One does one bathroom, one the other, if two baths. Split the the load of the two boilers around the taps in the house. Then it will be cheap to run, probably less than one condensing boiler dling the whole house, as most of the day the upstairs will be timed off. When going to bed the downstairs cam be off 1/2 hour before and upstairs then on. No down time if one fails, always heat in the house and hot water.

Easy to fit, easy to wire up (a doddle. To zone using any other system is complex using zone vales and complex wiring for a DIYer), simple, effective and cheap. Worth considering.

[IMM]

To avoid cycling most boilers has integral anti-cycle devices, and if you have a good timer/stat, e,g., CM67, these also have an anti-cycle function too.

[Tony Bryer]

The ones that seem to have been really problematic are upfiring - especially the Potterton Envoy. The downfiring design (Keston, Worcester etc) is effectively self cleansing.

I'm just installing a Glow-worm 24Cxi which I think is described as radial: it looks like the burn is horizontal (as with an oil boiler) and any debris falls out the bottom so hopefully will be OK. IMM suggested the design came from Holland: the flue adaptor has 'Vaillant' moulded into it so it appears that there is some design sharing going on.

The documentation could be a bit better: the electrics are easy if you are just installing a volt-free stat - for adapting existing mains controls the incomplete info leaves you guessing [or probably phoning tech support later this week]; under servicing they give you detailed instructions on how to disassemble the burner then tell you not to do this when carrying out a routine service!

[Tony Bryer]

I specifically chose the Glow-worm over a Worcester because it will modulate down to 4.9kW (as will the 30Cxi; 6.6kW for the 38Cxi) and as it will be in an open plan kitchen living room I hope it will be happy to idle away on low rather than cutting in and out which is much more obtrusive than steady background noise. According to the docs the 30 (and presumably 38) ramps up the heating output rather than going in at full blast (can radiators fail from thermal shock? )

[Christian McArdle]

That's good. It sounds like the burner is based on the MAN boiler, which has excellent modulating properties.

Christian.

[IMM]

Tony, cam you override the load compensation control for thermal store use?

[IMM]

The Glow Worm is a class act. Well in that price range it certainly is. We expect a user report on its operation.