Vaillant Ecotec 600 series boiler sizing

[Locoblade]

Hi All

We're about to get our old back boiler replaced with a system boiler, Ive found an RGI who's been recommended to me by family and he's given us an estimate we're happy with, but although he's made a suggestion, he's left it to me to ultimately decide on the make and size of boiler.

Regarding output, his recommendation is to over-size so there's always enough power at full demand, saying that it will modulate when there's less demand so there's no real problem with it being too big. I can understand this logic but I'm still worried the recommendation is overkill, even taking this into account and Im worried it may not modulate low enough to maintain maximum efficiency if its grossly oversize.

We have an 8m x 8m 3 bed semi with recently built 5m x 2.5m single storey extension, we've got partial cavity wall insulation (couldnt do it all due to tiles on the 1st floor front/rear walls), well insulated loft and ~20 year old UPVC double glazing. We have 9 radiators (all fairly large for the room size) and one indirect hot water cylinder.

Using the whole house calculator with slightly conservative inputs such as saying no cavity wall insulation at all, it gives me a figure of 11Kw output, yet I'm being recommended to go for a 24Kw or 28Kw boiler, over double what the sedbuk website suggests. For comparison I think our existing boiler is 45,000BTU (13Kw?) and it seems to heat the house OK, so I was thinking more like an Ecotec 618 so it could modulate down to around 7kw if needed?

Your thoughts and comments on the technical aspects and the suitability of each of the options would be most appreciated, thanks in advance.

 

[spudkey]

I would find an installer that knows what he is doing you are paying a professional HE should be sizing the boiler properly.
Get other installers in to quote[/url]

 

[Locoblade]

Been there, done that unfortunately, I've had 3 other quotes and was utterly unimpressed by all of them to the point of being disillusioned with the whole exercise, for example one was quoting to supply a Ferroli because "its just as good as anything available on the market" yet the price didn't reflect the budget choice of boiler.

This chap I'm going with is old school but he comes well recommended and the price is right hence me asking for opinions on the technical aspects of the above, because I knew there would otherwise be comments on my choice of RGI.

cheers

 

[spudkey]

go for a 615 0r 618 depending on your hot water cylinder, max heating output can set on the vaillants, dont oversize its pointless

 

[Locoblade]

Thanks so more along my lines of thought then. We'll be replacing the existing tank as its well past its sell by date anyway, looking at around 150-180L capacity vented tank I believe, we only have one bathroom and rarely use the bath, just shower which is currently electrically heated but may become pumped power shower when we re-do the bathroom next year

 

[spudkey]

connect any zone valves via the vaillant VR65 wiring center this will then allow you to run lower heating flow tempreture during warmer months, the boiler temp will then rise when hot water is called for to reheat cylinder

 

[gas4you]

DON'T oversize a Vaillant. You will be asking for trouble. Their HE's don't like excess heat that cannot be dumped into rads.

Go for the 615 or 618 and have it commissioned to your actual needs, this will give you a bit spare for the future.

I get the feeling this installer is not really up on Vaillants

 

[Locoblade]

Cheers for the info chaps.

Dave, I'm sure you're right regarding his experience with Vaillants and in an ideal world I'd obviously prefer someone who knows them inside out as some of you guys seem to, but finding such a person locally seems to boil down to pure luck, so without spending several more weeks inviting more RGIs round then waiting for quotes (which I know some of you guys don't like doing), that's not going to be possible because as mentioned I've lost the will to live with the local RGIs I have contacted so far, and Im not sure I could cope with too many more like that! One was actually Vaillant registered and I got his number from their website, yet he was the one recommending a Ferroli! All of them also advised against weather compensation controls when I mentioned it, because "they're too complicated" or "of no benefit", but then all but admitted they'd never actually fitted them before. One even eyed up our existing £20 Sunvic programmable room stat with distain because he didn't like "complicated controls"


Because of that, I'm content with chipping in with some of my own research and using with the chap I have to do the install, despite his lack of knowledge on this specific boiler. I think to be honest most of his work is done for housing association companies fitting/servicing low end combis etc which may explain his flawed "bigger is better" theory.

Regarding controls, although I'd still like to investigate weather comp at some point, I think at the moment to keep it simple we'll either keep our existing (fairly new) controls or go with a regular Vaillant setup if the VR65 requires them, which I'm suspecting is the case?

cheers

 

[gas4you]

Contact Vaillant enquiries, e-mail will do. They will get a couple of engineers on their approved list to come and quote for you.

They do in my area anyway, usually me and my mate follow each other around the same quotes

I always find it strange how prospective customers don't realise that a lot of us are all mates and know who is quoting for what in our areas