Boiler options

[Adam]

Hey all,

Time to access your boundless wisdom again!

We're considering options for replacing our current ch/dhw system. We currently have a gas-fired boiler and tank with a pathetic (7.5kW) electric shower. The tank is shoe-horned into a small cupboard at floor level in the loft-conversion, at pretty much the same height as the bathroom, with the header tank in what's left of the loft - maybe

2m higher. We seem to have the worst of all worlds: a *truly* pathetic shower, a bath that takes 15 minutes to fill, a not-desperately-efficient boiler and wasted energy from the hot-water tank (which isn't well insulated).

I've had a bit of a look, using this site and the FAQs, at the alternatives, and it seems to me that what we want is a combi. I need to test the mains flow rate (seems pretty good, though), but as we only have a single bathroom and there is not going to be any need to run baths concurrently with showering (plus, we aren't that fussed about slow bath-running) it seems a heatbank arrangement is overkill. There are only two of us with no plans for expansion at the moment. What are your thoughts?

One of our greatest concerns is the efficiency of the new arrangement

- ignoring, for the moment, the environmental impact of chucking out all the old stuff and replacing it. With the inefficiency of our current system, I guess we'll start saving pretty quickly...

I've checked the SEBDUK database and got the list of 50 most efficient boilers - we'll probably select the most suitable from that list. Can anyone give any extra insight into particularly suitable models?

Thanks again in advance for you help!

Adam...

[Christian McArdle]

You don't give a budget. Assuming you want a well regarded midrange model rather than a cheapie, the Worcester-Bosch Greenstar Highflow 440, recently discussed might be appropriate. It will provide a good shower and still manage to fill a bath before Christmas, if not at the rate of a heat bank, unvented cylinder or pumped gravity system.

It uses a small internal heat store to give enough reasonable flow to mostly fill your bath (depending on size) before cutting back to 11 litres a minute, which it can maintain indefinately. 11 lpm at mains pressure is enough for a decent power shower, but not a wide bore low pressure drencher type, or a panel type with body jets.

If you prefer a high flow instantaneous combi (probably more appropriate for a drencher shower), then there Bosch-Worcester have Greenstar versions up to

40kW.

Christian.

[Christian McArdle]

P.S. to compare with your electric shower, it is perfectly reasonable to suppose that the increased potential flow rate will be proportional to the rating in kW.

A 40kW combi will produce over 5 times the shower flow of your electric shower. A really basic 24kW combi will produce over 3 times as much, which will be enough to make the shower really quite pleasant, if the shower head is chosen wisely.

Christian.

[IMM]

Please behave. It will deliver 20 litres per minute filing a an average bath in less than 5 minutes. Most people don't care of a bath fill at 5 or 2 minutes. They really couldn't care.

Giving 16 litres.min. With cold added probably about 20 litres min, but for ever.

[Christian McArdle]

Given that the flowrate is calculated at 40C, why would you be adding cold?

Christian.

[IMM]

Do they say 40C temp rise? Well 16 litres hot only, which is a very good shower indeed, and too much for most people.

[Christian McArdle]

No, I mean at a 40C output temperature. It is standard nowadays to calculate using 35C delta T, equating to a incoming temperature of 5C. Summer flow rates will be higher.

Christian.

[Andy Hall]

That would be impossible in the winter with a cold mains temperature of typically 5-8 degrees.

WB may make reasonable products but can't override the laws of thermodynamics any more than you can.

.andy

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[IMM]

Do you think they telling porkies?

[Christian McArdle]

No, you are by suggesting that you can add cold water to the hot. The flow rates specified are at usable temperature (in winter) and can't be further diluted with cold.

Christian.

[Adam]

Sorry, remiss of me. Yes, mid-range should be good - ultimately, I'd rather stretch the budget for a boiler and not have to worry about it again for a good long time...

We're probably not going to be bothered by bath-fill times, so an internal heat store may be unnecessary. Not bothered by fancy showers (body jets, etc.) but would like a decent reasonably powerful shower.

OK, I'll check them out.

Thanks Christian (and everyone else who's contributed).

Can I assume that this is a tacit agreement that a combi is the best bet for our arrangement?

Cheers - Adam...

[IMM]

I think he means mid-range as mid in flowrate performance. The W-B Greenstar HighFlow is a Greenstar boiler with a heat bank all in one washing machine sized case.

It will give one. If you want a wall mounted job the Greenstar combi's will one. They have models of various flowrates.

Yep.

[Adam]

Sorry, a question I forgot to ask: do you know how much? Can't find much info on their site...

Cheers - Adam...

[Andy Hall]

Not as far as they go, but they are not being complete in their specification and are presenting the product in a better light than its ability to perform.

Even that Alpha thing that was your special offer last month had a more complete spec.

.andy

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[raden]

In message , IMM writes

Fuck off

[Christian McArdle]

Ouch. The price isn't small for the Highflow.

From

who are usually somewhere near the pace.

Greenstar Highflow - 1939 inc VAT Greenstar 40HE - 1297 inc VAT

Christian.

[Christian McArdle]

And given the price differential, an instantaneous type may suit you better.

You'll get good shower performance from a 28kW combi. 40kW will do two reasonable showers simultaneously.

Christian.

[IMM]

They do claim a two bathrooms, although I would say 1.5. That price is vs. good for a condensing boiler and an all inn one mains pressure simple installation. If you install it in an awkward location then it is the business. The internal condensate pump and long flue lengths then come into focus.

[Andy Hall]

In that case I don't see the point.

This device needs a washing machine space plus another 200mm access, so probably suited to a garage.

For that money, you could get a decent combi or system boiler and a pressurised cylinder or basic heatbank. The cylinder would take approximately the space of the Lowflow and then the boiler can be located easily separately.

.andy

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[Christian McArdle]

Indeed. The combination was considerably cheaper when I installed my heat bank and system boiler. Also, the flow rate provided is not that much greater than the 40kW instantaneous. I fear that they may have priced this boiler out of the market.

Christian.