replace system boiler with combi boiler ?

rakesh5883

I an just about to my new house in the next few weeks. Just had to take a builder around to get a quote on some bathroom work etc.,

In the new house there are 2 bathrooms ( 1st floor & GF) , and there is a Conventional boiler. He's asked me to replace this with a Combi boiler as it is more efficient and it make less noise as the current one has the pump fitted and all that !!

What i dont understand is that combi boiler when i read this online :

A combi gas boiler system is better suited to a home with a smaller number of people, as you'll only be able to use hot water from a combi boiler system for one task at a time. For example, one person wouldn't be able to have a shower while someone else does the washing up using hot running water.


Is this not for everyone ? and how do I know if this will work for my house or not ?

Can someone please share their experiences on this , good .. .bad ..ideas...please ?

Its a 4 bedroom house,
-with 13 radiators and 2 bathrooms
-currently we have a system boiler with cold water in the loft
- hot water tank in the 1st floor

Cardew

It seems to me your builder is getting what is easiest for him, not you. I have previously had some combis and currently have one in an annex to my house.

There are scores of posts on the merits of Combi v System boiler.

IMO the only real advantage of a combi is that it does away with two water tanks and hence makes more space available.

To suggest a combi for a 4 bed, 2 bathroom house is madness - again IMO. Your quote in italics sums up the situation perfectly.

Regardless of a Combi or System boiler a pump is still needed; how else is water pumped to the radiators? The pump can be internal in the boiler or external.

Where does your plumber get the information that a Combi is more efficient? Easy enough to research that on-line.

If you want a real upgrade to your Hot Water supply, get an unvented tank. It is expensive to install but you get copious amounts of hot water at mains pressure.

Ectophile

A combi boiler is an instant water heater, unlike a system boiler which can heat the water in the hot tank in slow time.

At this time of year, the incoming mains water is really cold (as the ground it's flowing through is cold). A combi boiler will struggle to heat a good flow from cold to acceptably hot. A decent power boiler should manage one hot tap OK. But depending on how the system is adjusted, if you try to turn on two hot taps at once, you will either get a miserable dribble of hot water out of whichever tap is higher up, or else you will get vaguely warm water out of both.

That's why combi boilers are recommended for flats and small houses.

J_B

Ectophile wrote: »

At this time of year, the incoming mains water is really cold (as the ground it's flowing through is cold). A combi boiler will struggle to heat a good flow from cold to acceptably hot. A decent power boiler should manage one hot tap OK. But depending on how the system is adjusted, if you try to turn on two hot taps at once, you will either get a miserable dribble of hot water out of whichever tap is higher up, or else you will get vaguely warm water out of both.

That's why combi boilers are recommended for flats and small houses.

Methinks you talk untruths.
The 'ground temperature' (where the pipes are) varies little from summer to winter.

If combi's were so carp as you suggest, why are they sold in such quantities?

Get one sized big enough for your needs - simples.

Cardew

J_B wrote: »

Methinks you talk untruths.
The 'ground temperature' (where the pipes are) varies little from summer to winter.

Whilst you are largely correct about the underground temperature variations, that is only part of the issue. The temperature at the source of the supply water in reservoirs/water towers etc has a large effect, as does the usage from the mains supply.

If you look on-line there are plenty of websites giving the seasonal range of temperature of mains water. The quote below is typical:

Worked in water treatment industry for 40+ years





Because most water supply pipes are underground they are quite well insulated from the extremes of weather. My cold water temperature in Cheshire varies over the year between 15C to 5C

Ectophile

J_B wrote: »

Methinks you talk untruths.
The 'ground temperature' (where the pipes are) varies little from summer to winter.

If combi's were so carp as you suggest, why are they sold in such quantities?

Get one sized big enough for your needs - simples.

I used to live in a flat with a rather weedy 23kW combi boiler.

In the high summer, I would fill the bath with a roughly a 50/50 mix of hot and cold water. In the depths of winter, it would end up all hot water and no cold at all.

The difference in cold water temperature between summer and winter can be quite substantial.

I notice much the same effect using an electric shower in summer vs. winter.

System

You need to get the views of a number of installers. I am getting a new system boiler installed next month and my installer not only measured the house but he also checked such things as water pressure before stating that my property was best served with a system boiler. We then had a discussion about whether it should be 18 or 24kW for a 5 bed house and he concluded that, whilst there were efficiency benefits from going for 18kW, the need to re-heat the hot water was the determining factor.

FWiW, one installer told me that I would be disappointed with anything less than a 35kW boiler - even though my present (very old) boiler is only 24kW.

Edvin_Paus

The Vaillant ecoTEC[/URL] 831 Plus 31kw boiler is well suited to 3 or 4 bedroom properties that have one or even two bathrooms. Choosing the right boiler for your home and for your needs is one of the most important home buying decisions we make. Understanding your home energy requirements helps you pick the right boiler! Therefore, you’re probably wondering how it all works. Well, the 30kW combi Boiler, works by taking the cold water straight from the mains supply and heating it through the boiler system on demand. This eliminates the need for having a separate hot water storage tank or cylinder.

Cardew

Edvin_Paus wrote: »

The Vaillant ecoTEC[/URL] 831 Plus 31kw boiler is well suited to 3 or 4 bedroom properties that have one or even two bathrooms. Choosing the right boiler for your home and for your needs is one of the most important home buying decisions we make. Understanding your home energy requirements helps you pick the right boiler! Therefore, you’re probably wondering how it all works. Well, the 30kW combi Boiler, works by taking the cold water straight from the mains supply and heating it through the boiler system on demand. This eliminates the need for having a separate hot water storage tank or cylinder.

I don't think there is any confusion about how a Combi boiler works - even by the OP. He has raised a query on the wisdom of replacing a system boiler with a Combi in a 4 bed, 2 bathroom house.

Look at the specification of a combi for the flow rate. This is normally given as the delivery rate of the mains water raised by 35C - so around 40C during winter.

I have a new (1 year old) 26kW Combi in a small annex. In winter it gives a reasonable shower - with the water at 40C(the boiler water temperature is displayed). However if you turn on the handbasin tap the effect on the shower is noticeable.

The other problem with a combi, in some situations, is the length of time(and water wasted) before it reaches full temperature at the tap/shower. Some boilers have a small internal tank which is kept heated to reduce the delay in hot water reaching the tap/shower.

The problem with this system, as has been reported several times on MSE, is the boiler fires up - often in the middle of the night - to keep that tank up to temperature.

System

I agree 100% with Cardew, There is a lot of maths and science involved in choosing the right size and sort of boiler. Unfortunately, unlike Germany where most heating advisers seem to have an engineering-related degree, our heating installers are not all of that calibre. Finding someone who knows his stuff is extremely difficult: I know: it has taken me over a year to select an installer.

AndyC123

I would have to agree here