Boiler Quote: Viessmann 30kw v 35kw

ach5

As I understand, the "litres-per-minute" output of hot water is important as well as your mains water pressure, not just the KW spec.

You could have a 35 KW boiler, but if you have weak water pressure then you wont get many litres-per minute through your bath taps.

A 30KW boiler with 12 or 13 LPM output will fill a bath in 10 mins (depending on the size of bath), assuming your mains pressure is decent. A 24kw might also be adequate.

If your mains pressure is weak, then you could have 45KW and you wont notice the difference over a 30KW one.

I am no expert, but I had exactly this conversation with my very knowledgable plumber about 5 hours ago!

bajangal

Ach5: Thank you and to your plumber. The mains pressure is very good. If I put the plug in the bath whilst using the over bath shower, by the time I have finished washing my hair and having a shower the bath is at a good "bath" level.

gas4you

You will find a 28/30Kw combi will cope with your demands.

A 35Kw will give you a stronger shower, but may not be able to be range rated lower enough for the heating requirements.

bajangal

Gas4you : Can you explain further what this means : "... but may not be able to be range rated lower enough for the heating requirements." In addition to having hot water, having constant/adequate heating is equally as important. Thanks.

noodlepie

I assume you don't have an electric shower. I you have an electric shower and don't intend having a thermostatic shower fitted then get a lower Kw boiler. Combi's are great for thermostatic showers. I could'n t live without one.
I can't find the modulating range for that model of boiler. I would'nt have that model of boiler in my house either. I'm not a snob I just would'nt take the chance. Get a Vaillant Pro or a Worcester-Bosch Greenstar. If you want to splash the cash upgrade to the Vaillant Plus or the CDI range.
The Kw rating on boilers indicates the maximum the boiler will run at. Not what it will run at. If its a good boiler it will "modulate". Modulate means it will run according to the system requirements (there is a range of modulation which effects efficiency and gas usage). Its complicated stuff, so just buy a good brand, get it fitted by someone who knows what they are doing and then you don't have to worry. As the installer tons of questions about the modulation setting and how the temperature of the water (in teh heating pipework) affects the amount of gas used. I believe you want it set a 68, but thats if your radiators ar up to spec.
It will frustrate engineers who don't know it, not all will, but there should be someone they can at least phone to find out.
What a messy threat.

gas4you

bajangal wrote: »

Gas4you : Can you explain further what this means : "... but may not be able to be range rated lower enough for the heating requirements." In addition to having hot water, having constant/adequate heating is equally as important. Thanks.

All modern boilers need to be set for the maximum output they will perform at to match the radiator outputs (range rating).

In a house with, lets say 12 radiators that have a combined output of say 15 Kw, you would either fit a 15 Kw boiler, or fit a combi to suit your hot water needs then range rate the heating output down to 15 Kw.

The boiler will then only modulate between 15 kw and its minimum output, which could be anywhere between say 6Kw and 10Kw.

If you only have 4 radiators with a heat output of say 8 Kw, then a boiler that has a minimum setting of 10Kw will always be too powerful for the heating so instead of modulating, will just switch on/off repeatedly and not stay in condensing mode long enough to be at its most efficient.

Instead of range rating, one could fit the rolls royce of boilers, ATAG, where they are designed to start off at minimum output and ramp up to the maximum needed for the rads.

Most other makes start off at max then modulate down so unless they have been range rated they will eg be trying to dump 24kw of heat into 10kw of rads. Not good for the boiler, or efficiency.

Lady_Tara

bajangal wrote: »

Been quoted for new combi boiler. Two bedroom detached bungalow. Mainly 1 person. Removing hot water tank from airing cupboard and boiler from kitchen wall. Can you cast your eyes over these quotes and I welcome your feedback. Both of these are from Gas Safe companies. Thank you.

I've just had the Veissmann vitotrol 100 35kw fitted in our house, 4 bed det, 2 showers, 1 bath, 3 toilets; tested the bath/showers this morning when everyone was getting ready and 2 showers ran fine at same time as filling bath . I paid £3200 inc VAT for fitting by veissman trained chap so get 5 years parts/labour guarantee. He moved location of boiler from util to upstairs, and did a few other bits for us including stripping down both showers cos they were full of cr*p. But I have found some bad reports of the 100 series, so hope I don't regret it We had 4 quotes and they were all around the same mark. Anyway, so far so good
PS we are in the midlands

bajangal

Lady_Tara wrote: »

bajangal wrote: »

Been quoted for new combi boiler. Two bedroom detached bungalow. Mainly 1 person. Removing hot water tank from airing cupboard and boiler from kitchen wall. Can you cast your eyes over these quotes and I welcome your feedback. Both of these are from Gas Safe companies. Thank you.

I've just had the Veissmann vitotrol 100 35kw fitted in our house, 4 bed det, 2 showers, 1 bath, 3 toilets; tested the bath/showers this morning when everyone was getting ready and 2 showers ran fine at same time as filling bath . I paid £3200 inc VAT for fitting by veissman trained chap so get 5 years parts/labour guarantee. He moved location of boiler from util to upstairs, and did a few other bits for us including stripping down both showers cos they were full of cr*p. But I have found some bad reports of the 100 series, so hope I don't regret it We had 4 quotes and they were all around the same mark. Anyway, so far so good
PS we are in the midlands

Thanks Lady Tara. Your comments have been helpful. I have decided to go for the 30kw because I only have 1 bathroom and at the most, 2 people in the house at one time.
Can I ask, did you have a magnaclean or similar fitted? The plumber that I plan to use is totally against them.

gas4you

You are are always best to have a magnaclean or similar device fitted, as you can never get an old system 100% clean by just flushing it.

What device is fitted is immaterial, as long as you have one fitted.

Lady_Tara

bajangal wrote: »

Lady_Tara wrote: »

Thanks Lady Tara. Your comments have been helpful. I have decided to go for the 30kw because I only have 1 bathroom and at the most, 2 people in the house at one time.
Can I ask, did you have a magnaclean or similar fitted? The plumber that I plan to use is totally against them.

Erm, not sure to be honest, I know he's put Fernox F1 in