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Combi boiler for 3 bath house?

(16 Posts)
JugglingChaotically Sat 15-Mar-14 09:53:03

About to redo plumbing and pressure hot water system. Have used a combo before bit can they work for a house with 3 showers? Worried that running kitchen tap while DDs in never ending showers could cause a problem.
(Though could be a way to cut them short I guesssmile)
Does anyone know if combis can deal with this? Also the one I had before was small. Worry this would be huge and hoping to gain space by this not lose it!

TheOneWithTheNicestSmile Sat 15-Mar-14 12:18:26

Piglet John will say no grin

He always talks about megaflow boilers - but I think you need a hot-water tank with them

JugglingChaotically Sat 15-Mar-14 12:54:51

Ah. Had one of those in the past too. Boiler plus water tank with bubble on top!!!
Was hoping not to as have almost no storage in house at all and we just seem to get more stuff as DCs get older...... Now storing tents, sleeping bags, huge rucksacks etc etc

TheOneWithTheNicestSmile Sat 15-Mar-14 13:04:11

well there certainly are combis which claim to be able to cope with more bathrooms & they're only a bit bigger than the ordinary ones

Worcester 42cdi is their biggest

wonkylegs Sat 15-Mar-14 13:14:34

My dad has a large combi for a 3 bath, 5bed house - he's actually got the one down from the one shown in the previous post.
He has little problems with the hot water but I think it only gets tested simultaneously when he as visitors.
He does find it's undersized for the house and on very cold days it struggled especially if you needed HW & heating at the same time.

We were told you could heat our very large Victorian semi with a combi but it would struggle with high demand scenarios. We ended up going for a Worcester 42cdi conventional boiler (on the kitchen wall in a cupboard) and a megaflow cylinder in the loft but we did have the luxury of a massive empty loft. It works well for HW & heating and the showers are wonderfully powerful even when DH helpfully puts on the washing.

ilovepowerhoop Sat 15-Mar-14 13:15:06 - would a sealed system boiler be more useful in your situation (doesnt need a cold water tank in the loft but does need a water cylinder)

PigletJohn Sat 15-Mar-14 14:40:10

No (obv)

For some reason people think that to buy a modern, efficient boiler, it must be a combi. this is not true.

A combi is especially suitable for a single-occupancy house where there will only be one shower or tap in use at a time. For you....

Fill a bucket at the kitchen sink, time it, calculate how many litres per minute you have.

PigletJohn Sat 15-Mar-14 14:53:19


am amused by the dad with a combi and three bathrooms, and is OK unless they are used.

JugglingChaotically Sat 15-Mar-14 15:07:25

Thanks all. I guess good pressure water warm house and space too much to ask for!
PigletJohn - they built new houses nearby recently and so water flow def down. How many litres/minute do we need?

PigletJohn Sat 15-Mar-14 15:12:49

12 would do for a single shower

20 is much better for a whole house, though you would need a very big combi to hear that much, a conventional boiler plus a Megaflo could do it.

It may be that your house has a half-inch water pipe out to the main in the pavement. Digging a trench for a bigger plastic pipe would make a big improvement to flow.

JugglingChaotically Sat 15-Mar-14 15:19:11

Thanks- will check. Think we still have the old lead main. Is it above job to replace. We are planning on doing lots of work and tight on £ so we will have to cut something else to do this. But sounds like it needs doing as no point in showers that dribble or can't be on at same time.

PigletJohn Sat 15-Mar-14 15:27:19

you might qualify for a Lead Replacement Subsidy. Contact your water co and ask them to test your drinking water for lead. Request this at once, they may be very slow to do it.

Look at the terms of their Lead scheme, with luck, if you replace your part of the pipe, they will replace their part too and perhaps save you having to pay them to dig and connect in the pavement.

A 25mm plastic pipe will be much better than half-inch lead, but 32mm costs little extra and is better still. You may need to change some of your internal pipes as well so you don't strangle the flow.

MrsTaraPlumbing Sat 15-Mar-14 17:08:25

The right sized combi can heat a very large house (ref Wonkylegs) and you can get them with very large outputs.
The problem comes when you need to draw hot water for a long time.

The boiler will prioritise heating the hot water, in other words it can't heat your house when you have a hot tap on, in our house most of the time that makes no noticable impact but if we all have a shower one after the other that could be an hour or so with no heating on.

As I said on another post today if ALL the conditions are right you can have a combi in a family home with 2 bathrooms (such as ours with 5 people living here), but I would not recommend a combi for a 3 bathroom house.

BTW, even if you don't buy a Worcester Bosch boiler their website is very good and paced with useful information. (I usually look at the technical site for installers - which you can look at too, buy I'm sure the site for homeowners is also detailed.

MummytoMog Sat 15-Mar-14 19:18:39

We have one in our five bed, three bath - it's a bit under specced as we installed it when we only had one bathroom, but one of our showers is electric and our children are small. We also mostly heat our downstairs with the woodburner. So far it has manage to heat the upstairs very nicely indeed, but we only have three radiators in the whole downstairs and it's chilly without the fire going. Luckily, the fire is always going.

We have a Worcester Bosch Greenstar. I think it's 28cdi, and I do regret not going up a size when it was installed.

PigletJohn Sat 15-Mar-14 19:31:41

the 28cdi is 24kW output, which is a fair amount. When the house feels chilly, is the boiler firing constantly at full power, yet the radiators are not fully hot? If not, it may be that your radiators are undersized and can't deliver as much heat as the boiler is capable of providing. As a rule of thumb, a single radiator 600mm high and 1000mm long can output about 1kW of heat, so your boiler would be capable of running 24 linear metres of radiator (because of the way the calculation is done, you are better off with more radiator). Accurate figures depend on single/double; fins; and pipe connections.

It's quite common for houses to be cool because the radiators are too small, and it might not be too expensive to fit bigger, or doubles in place of singles..

MummytoMog Sat 15-Mar-14 21:53:21

I'm pretty sure it's because we don't have enough radiators downstairs. Upstairs there is one in every room and it's toasty, but downstairs there is only one very long ancient radiator in the big living room, one tiny old one in the hall and one new double radiator in the extension. I really think I should have had another double, but I'm planning to whip out the two old ones and replace them with doubles in the autumn.

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