Replacemnet boiler help

[mdj1]

Hi All,

We've just moved into our new home :~) and although the boiler works fine, it's the original back boiler from 1970 and I would say not very efficient.

So, I would like some advice on a new boiler.

I would like to move over to a condensing boiler, placed in the loft so I can remove the airing cupboard tank in preperation for an en-suite at a later stage.

There are only 2 of us in the house (3 bed) at the moment although I'm sure this will change in the future.

There are 8 Radiators at present 9 when the en-suite goes in, and we will have 2 showers.

I've had the water pressure measured and it's coming in at 6 bar.

A friend has suggested a 30kw glo-worm? and already told me that the loft will need a light, boarded from the hatch to the boiler and also a fixed loft lader.

Any advice will be greatly apprciated.

 

[Agile]

You should have dealt with this two months ago when you could have had a £400 scrappage donation.

There is no problem replacing your boiler but only take advice on site from a gas registered person who can consider all the requirements.

If you want a combi ( not my choice for a three bed house! ) then you need the flow rate measured. The pressure is pretty irrelevant although suh a high pressure may need a reducing valve.

Tony

 

[ianniann]

You don't say explicitly, but it sounds like you're planning on a combi boiler. The condensing part is pretty much a given since you'd have to work really hard to get anything else now.

Have you considered whether you will in future need to support two showers at the same time? A shower and other demand for hot water? These are things that a 30kW combi won't do very well. The two showers at once would be just about unworkable and even someone running a hot tap would probably be too much. There are more powerful combis that can provide more hot water, but it sounds like you don't need a huge one to heat your home. Just something to consider. You can certainly use the 30kW (or less) just so long as you appreciate the limitations.

 

[ianniann]

If you want a combi ( not my choice for a three bed house! )

Not your choice for any house, I think Tony? Large houses have multiple bathrooms, so combis are bad. Small houses don't need a 30kW boiler so combis are bad

 

[Agile]

I have nothing against combis where they are the best choice.

They are 96% of the boilers that I repair.

But they are only suitable for one bathroom properties with one occupant like a small flat.

With two people and one bathroom they are still OK if the second person holds off washing up while the boss is in the shower.

Tony

 

[PEDANTICVINDICTIVEMAN]

Sounds good to me, a combi per bathroom/ensuite, 4 combis all to repair and service, EXCELEEEEEEEEEENT

 

[mdj1]

Ahh man!

Can't believe all the £400 vouchers have been used up! A*holes!

We didn't move in until the weekend and I was told I couldn't apply until this time.

 

[Agile]

The boiler scheme cost the Government real money unlike the car scheme which was in effect a discount on the car/vat charge and so self financing.

There were about 2,000,000 boilers which could have been replaced and the limit of 125,000 was just a taster to encourage prople to think about their heating systems.

It did that and was effective for that purpose.

Tony

 

[mdj1]

The annoying thing is I called them 7 weeks ago and they told me I qualified but to call back when I'd moved.

 

[Agile]

It was obvious to us that it would be used up within a very few weeks.

Too late now but you should have applied as soon as the scheme opened as if you lived there already.

Tony

 

[mdj1]

Sorry but it's really p**ed me off.

Another lost vote for labor on Thursday! lol

Anyway, so are combi's more efficient than tanks etc.

We only used to have the water on for an hour in the morning and in the evening and it seems pointless heating all that water?

 

[ianniann]

Combis are neither more nor less efficient than non-combi boilers. However, storing warm water for any length of time inevitably leads to heat being lost. You'll have to judge for yourself how much of this heat is lost and how much is wasted in your situation. Cylinders are fairly well insulated now, but they'll still keep an airing cupboard warm so you know they're losing heat. If they're in a loft then that heat is flat out wasted. If they're in an airing cupboard then you might find the heat useful and except in the middle of summer shouldn't be considered a total waste. The advantage is that you can dump the entire contents of the cylinder into a bath in a minute or two, when a combi would take quite a few minutes to heat the water for as it flowed into the bath. The disadvantage is that the pressure from a cylinder is far lower than mains pressure so you either get a weak shower or you need a pump to force it through the shower head.

Combis may also waste some heat. Many of them have a form of pre-heating that maintains the heat exchanger or primary water circuit at a high temperature so that hot water can be provided more quickly when you turn on the tap. A few also have small tanks included inside the boiler which can be kept hot. If your boiler is in a loft or garage then some of this heat inevitably leaks away and is wasted. The boiler fires periodically 24/7 to keep it hot. Some but not boilers all allow these features to be turned off, which slows down the initial time taken for hot water to arrive at a tap, but reduces the standby gas usage to zero.

There are also subtleties concerning how effectively a given boiler can stay in condensing mode when it is providing water through a combi or water into a cylinder. Either can be better or worse depending on the design and the way it is used. No doubt any two experts on this frum could give you three opinions about the best way to eke out that last 5% of efficiency when heating your water. For example, while maintaining a hot water cylinder at 70C, it is effectively impossible for the boiler to be condensing.

 

[D_Hailsham]

For example, while maintaining a hot water cylinder at 70C, it is effectively impossible for the boiler to be condensing.

But hot water cylinders should only be maintained at a temperature of 60C.

The return temperature needs to be 55C or lower for condensing to occur. So, if you boiler is running at 75/55 or 65/55, it will be able to heat the cylinder up OK and will condense.

 

[ianniann]

hot water cylinders should only be maintained at a temperature of 60C

Shoulda, woulda, coulda

if you boiler is running at 75/55 or 65/55, it will be able to heat the cylinder up OK and will condense

... and will start to condense. There is no massive all or nothing change from non-condensing to condensing at 58C. Condensing extracts steadily more heat from the exhaust gas as the return temperature drops. At a return temperature of 55C, condensing is only giving you an extra two or three percent, not the 10% or so that is the maximum you can extract. You will never condense every last drop, but a typical boiler design effectively maxes out on a return temperature around 30C.

 

[mdj1]

Thanks for the info guys.

So, energy efficiency wise there is not much difference these days. Combi boilers take up less space which is a plus, but are effected if more than one tap is working at the same time, good job most washers / dishwashers are cold only these days!

I'm also assuming that replacing the complete system of each that a normal boiler + Tanks etc are more expensive than a combi on its own?

Myself and the missus do like a nice powerfull shower, are we going to get this with a combi? I know you can't add a pump like in a gravity fed system, is the pressure from a combi going to equal that of a 1.5bar pump? or would a good electric shower straight from the mains give the same?