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Author Topic: new boiler what to go for?  (Read 3822 times)
spluger
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« on: May 22, 2011, 09:57:13 PM »

OK I'm after advice here apologies if this is not the correct topic for this post

My old boiler is finally giving up and I'll need to replace it before the heating season starts snow

but what type / fuel / technology would you recommend

house is well insulated DG cavity loft etc

Solar hot water and tank and system plumed in Y plan
unit would be wall mounted and no room for a big wood pellet burner
looking for a system type boiler to use but I've heard allot of modern condensing boilers are unreliable.

and I'm looking forward to even lower gas/energy bills once the new ones running

oh and budget would be as cheap as possible but willing to stretch for better tech etc

Cheers

David
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20 x 58mm tubes plumed direct , -10deg south facing 37 deg pitch, 200ltr vented standard tank
Fire Belly fb1 wood burner
2.5kW east west PV 2 x sma 1200
weather compensated boiler
supremetwo
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« Reply #1 on: May 22, 2011, 10:49:29 PM »

Read Miketheboilerman's web site; he is one of the leading experts in the South:-

http://www.miketheboilerman.com/

He fitted one of these to his own property:-

http://boards.fool.co.uk/i-also-would-hate-to-disgree-with-mike4s-12135878.aspx

http://www.discountedheating.co.uk/shop/acatalog/Vaillant_Eco_Tec_Plus_428_Heating_Boiler.html

Nuff said. Grin

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spluger
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« Reply #2 on: May 23, 2011, 08:15:23 AM »

Thanks for the link

i think he might be too far for me as i'm in Gloucester and i'll be paying his travelling

also i forgot to mention the current setup is a pressurised system so no expansion tank for the heating circuit.

 
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20 x 58mm tubes plumed direct , -10deg south facing 37 deg pitch, 200ltr vented standard tank
Fire Belly fb1 wood burner
2.5kW east west PV 2 x sma 1200
weather compensated boiler
supremetwo
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« Reply #3 on: May 23, 2011, 10:30:54 AM »

i think he might be too far for me as i'm in Gloucester and i'll be paying his travelling.

Mike does not install, he is a leading repairer and hence exposed to the problems of various makes of boilers.

He is very scathing about faults suffered frequently by some quite well-known makes and I'm not talking about blocked condensate drainage:- http://boards.fool.co.uk/building-diy-fools-50975.aspx?mid=12201368&sort=username

There is also much useful advice regarding boiler-change quotes among his TMF posts.

Vaillant offer a system boiler for pressurised:-

http://www.vaillant.co.uk/homeowners/heating-solutions/high-efficiency-boilers/System-boilers/

Hopefully someone else will recommend an installer in your area.
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spluger
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« Reply #4 on: May 23, 2011, 11:46:30 AM »

thanks for that lots of reading todo

nice to hear at least some makes are ok.

cheers
david
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20 x 58mm tubes plumed direct , -10deg south facing 37 deg pitch, 200ltr vented standard tank
Fire Belly fb1 wood burner
2.5kW east west PV 2 x sma 1200
weather compensated boiler
spluger
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« Reply #5 on: May 23, 2011, 12:22:02 PM »

Just did a boiler size calc onhttp://www.idhee.org.uk/calculator.html
and it recommends 7.38kwh for the boiler


so if thats correct do i go for a small boiler or a larger typical 24-28kwh type

also a smaller size could allow for other technologies to be used instead such as ASHP (not a fan) wood etc


David
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20 x 58mm tubes plumed direct , -10deg south facing 37 deg pitch, 200ltr vented standard tank
Fire Belly fb1 wood burner
2.5kW east west PV 2 x sma 1200
weather compensated boiler
supremetwo
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« Reply #6 on: May 23, 2011, 01:40:17 PM »

7.38kwh seems very much on the low side to me and I'd want to study their assumptions.

The method work sheet is available from the BRE on 01923 664258.
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Iain
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« Reply #7 on: May 23, 2011, 03:45:07 PM »

Hi
Have also been looking at a new boiler to replace my Worcester. So far have decided on the Remeha Avanta system boiler(http://www.avantarange.com/18s.html) with an Isense controller.(Outside temp sensor and cylinder sensor). This will allow weather compensation and also a temp/time program for the hot water cylinder, also does an anti leigionella program once a week as well if you want (will work with s plan and y plan as well). This will allow me to work around the solar thermal. ie need 45degc at 0700 in the morning for showers etc, but just the top of the cylinder,to allow for solar during the day. I can get 5 years parts and labour on this boiler. I have heard good reports on this boiler and it fits in with the solar thermal, will also modulate down to 6kw
Iain
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1.98kWp PV  (11 x Sharp 180 and SB1700)
20 x 65mm Thermal and 180ltr unvented
9000ltr rainwater storage   Plymouth
http://www.bdpv.com/fiche_utilisateur_en.php?util=iain
http://www.sunnyportal.com/Templates/PublicPageOverview.aspx?plant=cba8d47f-bf09-4533-a105-4303b353f20f&splang=en-US
wookey
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« Reply #8 on: May 23, 2011, 03:56:44 PM »

I've seen many people suggest that atag, wolf and viessman are all good quality gear, but all significantly more expensive than more run of the mill options. I've got a dinky viessman system boiler which is fine, but then it gets very little use.

When you say 'well insulated' do you mean 'current part L' level, or AECB silver or better, and more importantly how good is your airtightness? It's very hard to buy boilers small enough for genuinely well-insulated houses. The max power for DHW becomes much more significant than space-heating requirement. 7.4kW is perfectly normal for a fairly-well insulated and not-huge house. A genuinely well-insulated house  is more like 2 kW
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Brandon
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« Reply #9 on: May 23, 2011, 05:38:07 PM »

Just did a boiler size calc onhttp://www.idhee.org.uk/calculator.html
and it recommends 7.38kwh for the boiler


so if thats correct do i go for a small boiler or a larger typical 24-28kwh type

One of the problems that is come across with condensing boilers is that the secondary heat exchangers rot out, this is attributed to the boiler never being run at capacity, therefore I would go for a small boiler.

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spluger
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« Reply #10 on: May 23, 2011, 10:01:03 PM »

Wookey

house is well insulated 300mm fluff in loft 6" of poly beads in cavity pilkington K glass all around
i've done lots of air tight testing using large cooker extractor and a josh stick, last place to seal is pesky down lights in bedroom.


Brandon

partly my thinking is why have a over sized boiler as i would guess a smaller one would run more efficient flat out than a larger one ticking over!!
DHW not a problem as all it would mean is a longer heat up time.
oh and i'm planing a wood stove soon anyway for the really cold days.

David

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20 x 58mm tubes plumed direct , -10deg south facing 37 deg pitch, 200ltr vented standard tank
Fire Belly fb1 wood burner
2.5kW east west PV 2 x sma 1200
weather compensated boiler
insolare
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« Reply #11 on: May 24, 2011, 08:47:12 AM »

Don't oversize as it reduces efficiency and can cause shortcycling, although most boilers are fully modulating and better ones have anticycling circuitry and can be range rated to limit the ouput. Vaillant and Remeha combis and system boilers can both be limited in such a way. Vaillant are adjustable in 1Kw steps and I think the Remehas similar. Vaillant are great boilers and fitted by certain engineers (me!) come with a 5 year warranty on most models.

I have never heard of secondary (DHW) heat exchangers rotting out. They do get blocked but thats normally as a result of dirt (sludge) in the heating system or limescale deposits in a hard water area.
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nickiniquity
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« Reply #12 on: May 24, 2011, 09:12:29 AM »

+1 for not grossly over sizing... I've recently replaced a boiler in a house I let with a Viessmann 200w.with weather compensation controls (It's an awesome piece of kit!)   It's coupled to a hot-water cylinder and heats a three bed semi.  You wouldn't believe some of the boiler sizes from some of the less competent installers I invited to quote.  One was almost double my calculated heat loss, so I imagine it would have run very inefficiently as even on it's lowest modulation, it would be far too powerful most of the time.

There's some mixed views on having weather compensation, I think it is really worth having on a decent boiler, mine seems to use it to keep the boiler at the lowest possible supply temperature, condensing as much as possible, which must be saving cash.  The house is more comfortable too.  The downside is that you need to oversize your radiators.

I was intending to replace the ancient crock in our house with the same boiler (the rental house install was a 'taxback' funded trial!), but I've got plenty of space, so I'm seriously considering a log boiler install instead as I reckon the payback will be about half that of a gas boiler in my situation.

Nick
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supremetwo
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« Reply #13 on: May 24, 2011, 10:34:30 AM »

Don't oversize as it reduces efficiency and can cause shortcycling, although most boilers are fully modulating and better ones have anticycling circuitry and can be range rated to limit the ouput.

What do you think of the figures produced by http://www.idhee.org.uk/calculator.html?

To me they seem rather low.

What do you get from that site if you enter details of a known system that you have calculated by normal methods?

The last thing one wants is to be too cold in a severe winter (and you do not want potential clients querying your figures should they check).
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wookey
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« Reply #14 on: May 25, 2011, 02:09:44 AM »

Yes, it does seem a bit low. It doesn't mention ventilation - has that been forgotten? Putting in my house (1960s detached with cavity wall+loft ins+partly internal insulated+10yr-old DG+draughproofing) which I calculate loses 3kW through conduction and 4kW through air ventilation that site gives 3.8kW. Which is a reaosnably accurate estimate of conductive losses. In practice we can heat the house fine with a 5kW woodburner.
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Wookey
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