Which CH system????

[Crakkers]

OK, I wish to replace my 30 year old boiler, no not the wife, the thing that heats water etc.

I know I dont want a combi!

BUT All I get asked is do you want a conventional boiler or a system boiler and do you want vented or unvented.

Now I currently have vented and i've done my homework on the differences between the systems, but i dont know about advantages and disadvantages, especially in terms of running costs. Also what about boiler size?

I live in a 1930s 3 bed semi with one bathroom.

Can anyone help???????????

 

[GeckoGas-com]

This really is a very broad area....

I'll sum up my opinions....

Unvented HW
- More expensive to install
- Higher efficiency
- Needs to be maintaned every year
- Mains hot water throughout property
- No tanks in the loft

 

[Dan Robinson]

18kW boiler should be fine.

Running costs are set mainly by the boiler and the sage of the cylinder.

Unvented cylinder will have a slightly better heat retention than open vented but not so much that I would break a sweat worrying.

What else are you missing from your homework?

 

[Doctor Drivel]

This really is a very broad area....

I'll sum up my opinions....

Unvented HW
- More expensive to install
- Higher efficiency

Higher efficiency? Where?

- Needs to be maintaned every year
- Mains hot water throughout property
- No tanks in the loft

Some do allow high water pressures, however most are around 2.5 bar. They have Pressure reducing valves on them. Heat banks have higher pressures resulting in higher flows.

 

[Agile]

Most 3-bed semis work out at about 10-12 kW heating load. Adding 2 kW for water heating makes a 15 kW boiler adequate in almost all cases.

Worcester conveniently make 12-15-18-24 kW boilers to suit most applications. They have both system and OV boilers available. They are a little new for the medium term reliability to be known yet but so far they seem pretty reliable.

I would therefore expect that a 15 kW boiler would be adequate but it all depends on your insulation. Its best to uprate your insulation and then fit the coprrectly sized boiler.

Tony

 

[megawatt]

3 Bed semi with 1 bathroom ... What is your problem with a combi?

If you are not planning an extension or adding any more bathrooms then there are many combi's which will be more than capable of doing the job and which will provide for a simpler installation and lower maintenance costs.

I live in a fairly large 4 bedroom house (18 rads) with 2 bathrooms (both having baths and showers) and all is supplied from a Worcester Highflow 440 floor standing storage combi with far less complexity than any of the other types of installation.

Combi's have uses (and limitations) ... Horses for courses

MW

 

[Nixt]

Maybe the OP has noticed that the vast majority of other posts concern faulty combis.

 

[Agile]

If you are not planning an extension or adding any more bathrooms then there are many combi's which will be more than capable of doing the job and which will provide for a simpler installation and lower maintenance costs.

Whilst a combi would be quite adequate in many cases, its a much more costly job to convert a conventional system to a combi.

Thats only possible if the mains flow is adquate.

The existing system has all the advantages of a stored hot water system and can dump a bathfull of hot water in just 4 minutes, something no normal combi would ever achieve.

Whilst modern combis are more complex, their reliability is also now very high and maintenance costs and breakdowns are largely a thing of the past unless its a Sonya Duval.

Tony

Tony

 

[Doctor Drivel]

If you are not planning an extension or adding any more bathrooms then there are many combi's which will be more than capable of doing the job and which will provide for a simpler installation and lower maintenance costs.

Whilst a combi would be quite adequate in many cases, its a much more costly job to convert a conventional system to a combi.

It is? Not in my experience. It is a doddle.

The existing system has all the advantages of a stored hot water system and can dump a bathfull of hot water in just 4 minutes, something no normal combi would ever achieve.

Look hard. Look at the Alpha CD50, Viessmann 333, etc.

 

[megawatt]

Nixt wrote:

Maybe the OP has noticed that the vast majority of other posts concern faulty combis.

Maybe he is also sensible enough to realise that this is because combi's account for the majority of installations

 

[gas4you]

OP, I would also suggest, as Dan says, an 18Kw boiler. If it was one of the Vaillants I fit then you could range rate it down slighlty to around 15 Kw and still have some power spare.

A sealed system boiler is better as once filled correctly the water cannot be aerated again, therefore the entire heating system should last longer. You will not need a header tank in the loft either.

As to vented or unvented, if money is no object then go unvented as long as you have at least 3 bar cold mains pressure, >20 litres/m cold flow rate and a 22mm cold mains supply to run to it.

It will also need to be fitted by an unvented qualified engineer.

The advantages are balanced hot and cold taps in the bathroom and no need for power showers.

The vented option is a lot cheaper but you could need to add the cost of a power shower/shower pump to the upstairs showers.