What Boiler Option?

[duffy78]

I realise this question has been done to death so apologies for asking it again. I know that the answer in this case will be unvented but I just wanted to have another opinion as I have been given conflicting advise from people who have quoted.

Changing the boiler to get rid of the hot water cylinder and cold water tanks in the loft, so I can convert the loft into two bedrooms.

House is currently a 4 bed, 1 bath, 1 ensuite. 12 Rads. When fully developed will be a 6 bed, 1 bath, 2 ensuite, 15 rads.

Built in 1996 it has 75mm cavity walls which have since been filled. House is occupied by myself, my wife, 7 year old son, 5 year old son and 4 year old daughter. We will be living here until the kids leave home so I expect we will eventually become a high hot water demand family.

Water mains pressure into the house is v good at 25l/min and the water main enters the property adjacent to existing boiler installation.

I have been quoted and advised to use the following.

Worcester 42CDI = £2950

Worcester highflow - 440 or 550 = £3500 or £4000

Worcester 30i system boiler with 210l worcester greenstor = £4000


So I know that the combi is not going to suit our needs moving forward but have found the quote useful in that it gives a baseline comparison for the other options.

First question is should I be looking at a larger unvented cylinder? Heating Eng has suggested going for the 250l as a min as its only approx £90 more (I suggested the 210l)

Second question is would the highflow 440 be a happy medium between the combi and the unvented system?

And finally the Third, is a 30kw boiler overkill for the unvented system? Could we get away with a 24kw to help balance out the increased cost of a larger cylinder?

I'm pretty much sold on the unvented option at the minute due to beneifts in hot water provision and that it maintains the use of an immersion heater.


Thanks

 

[gas112]

6 bedrooms 3 bathrooms = lot of people you dont want a combi

 

[duffy78]

What about the combi storage option that has been quoted for?

 

[D_Hailsham]

When fully developed will be a 6 bed, 1 bath, 2 ensuite, 15 rads.

At an average 1.5kw per rad that means 22.5kW for heating plus say 3kW for the cylinder.

Use Whole House Boiler Size Calculator to check the boiler size. (Do it for the existing house then add in the rads for the loft conversion.)

Well insulated houses need very little heat. I have visited new 5 bed houses which have only 15kW boilers. They had two bathrooms and had an unvented cylinder.

If the system is configured for Hot Water Priority, there is no need to allow the 3kW extra on the boiler size. All it will mean is that, for the 20 minutes the rapid recovery cylinder is being reheated, the central heating is off.

 

[muggles]

I think you'll be disappointed with a storage combi, you really do need an unvented cylinder and separate boiler. I'd agree with your heating engineer - a 250 litre cylinder is the one to go for.

As for which boiler to go for, that really depends on the requirements for heating your house, although the coil rating of the cylinder should be taken into account. It's worth noting that the 24kw is slightly less efficient than the 30kw, so I'd maybe look at the 27i instead (although, in truth, if it was me I wouldn't be looking at Worcester at all...)

 

[duffy78]

Thanks for that.

Going to ask the guy to requote for 24kw boiler and larger capacity tank.

 

[doitall]

210Ltrs will be plenty, perhaps 99% of the time and an unvented is best by a million miles. (look up the price of a highflow replacement cylinder)

An alternative is a smaller combi, say 28kw serving the kitchen and utility and an unvented cylinder just serving the bathrooms etc.

Can be connected as a standard S or Y plan.

Sounds like you need to look for a good RGI/plumber for further advice and quotes.

 

[duffy78]

Sounds like you need to look for a good RGI/plumber for further advice and quotes.

I've had 4 guys round and to be fair to the last 2 that came their advice and also quotes have been the best.

Out of these two first guy said I could probably get away with the storage combi as the increased cost of unvented may put me off.

Second guy quoted both before making a recommendation and now he has priced up both has recommended unvented as the difference in cost is only £500 over a 440 highflow and inline with a 550 highflow.

The second guy spent a fair bit of time going over the routes of proposed pipes with me etc as he wanted to tie into the start of the hotwater piping in the current airing cupboard on both combi and unvented options

First guy would only do this in the case of unvented system. infact the others also wanted to tie hot water into the hot water tap in the downstairs toilet which backs on to the garage (boiler will be in garage)

 

[D_Hailsham]

It's worth noting that the 24kw is slightly less efficient than the 30kw

What 90.2% for the 24kW compared to 90.3% for the 30kW?

Statistically the difference is meaningless. There needs to be 3% difference before you can say with any certainty that one boiler is more efficient than another.

According to the Sedbuk Database the most efficient current Band A boiler is 90.3% efficient and the worst is 87.9%, which is a difference of 2.4% - less than the 3% needed to say that one is any better than the other.

You're a victim of the manufacturer's sales pitch.

 

[Agile]

.

Water mains pressure into the house is v good at 25l/min and the water main enters the property adjacent to existing boiler installation.

Thanks

"25l/min" is a flow rate and NOT a pressure.

It is also probably an open pipe flow rate!

It is the dynamic flow rate which is important! That needs to be about 10 li/min @ 1.0 Bar for each shower you want to use at the same time.

Yours is probably only 12 li/min @ 1.0 Bar. To get good performance you will need to upgrade your water supply.

I use the rule of thumb to size cylinders of 50 li plus 50 li per person which would give 300 li in your case. There is no point in saving £50 on the cost of a smaller cylinder. The installation and operating costs are the same for a 300 li cylinder.

Now its properly insulated the heat loss plus 2 kW for water heating is probably going to be less than 18 kW. Its less efficient to oversize boilers although so many do it because they just don't understand boiler sizing.

Tony

 

[duffy78]

thanks

Quote from the second guy include upgrading water supply from 15mm to 22mm from incoming potable water main to boiler.

 

[Agile]

That only relates to a combi boiler!

A combi of any kind is unsuitable for your needs!

Tony

 

[duffy78]

That only relates to a combi boiler!

A combi of any kind is unsuitable for your needs!

Tony

from the quote

Hot and Cold water conversion to sealed system and install 22mm copper cold supply and hot water retern to new cylinder.


So mistake in my terminology??

 

[doitall]

To be honest, You need to be looking at the right solution first and price second.

As suggested, if the garage is close to the kitchen/utility an 28kw combi serving the kitchen hot water, then an S plan serving the an unvented for the bathroom areas and heating.

The incoming mains needs to be at least 22mm with 22mm feeding the unvented.

You would probably need a secondary circuit (depends on layout) but the unvented could go in the garage with the boiler.

Lots of ideas you should discuss with the installers

 

[duffy78]

Thanks all,

from the start i have maintained to those that have come and quoted that I wanted an unvented system with boiler and tank in garage, some have talked me away from that, some have offered alternatives. Hence me asking for an opinion.

I guess those that talked me away from that kind of system were prob not accredited to install such a system, or just want to come and install a combi with the minimum amount of fuss.

What benefits would a combi serving the kitchen and then unvented serving heating and upstairs give me?