Sat, 02 May 2026 10:02:05 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=1131#Comment_1131 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=1131#Comment_1131 Wed, 14 Mar 2007 21:34:54 +0000 William Thing is, a few on-line calculators say I only need 14Kw. What am I missing , should I spend the extra £300 on capacity I don't need and waste energy too?

PS: Ive got 280m of UFH pipe]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=1133#Comment_1133 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=1133#Comment_1133 Wed, 14 Mar 2007 21:40:35 +0000 nigel If its a gas boiler most will modulate down to that sort of level.
Plumber have a tendency to overspec so you never complain of being cold, they dont care if its less efficient.

I suggest you find a smaller, modulating boiler.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2285#Comment_2285 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2285#Comment_2285 Wed, 18 Apr 2007 16:04:15 +0100 Guest Regards Wessex Energy Services]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2304#Comment_2304 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2304#Comment_2304 Wed, 18 Apr 2007 22:03:26 +0100 Paul in Montreal Posted By: WilliamMy plumber tells me I need a 28kw boiler for my 100 square metre new build , 2 bedroomed detached hoose.
Thing is, a few on-line calculators say I only need 14Kw. What am I missing , should I spend the extra £300 on capacity I don't need and waste energy too?

Even 14kw sounds like a lot! I have a 109 year old house in Montreal that is not well insulated by any stretch of the imagination (though it is reasonably airtight) and at an outdoor temperature of -20C (i.e. vastly colder than the UK) the heatload with an interior temperature of 20.5C is only 14.6kw - and this house is 181 square metres. We build a new house that is over 325 square metres and it's heat load at -20C is of the order of 16kw. Even your on-line calculator figure of 14kw sounds very high - especially if it's a new build.

Oversized boilers/heating systems become much less efficient than their rated steady-state figure.

Paul.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2313#Comment_2313 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2313#Comment_2313 Thu, 19 Apr 2007 11:16:28 +0100 Mike (Up North)
I think you were specified a 28Kw unit as thats probably what the plumber usually fits and an gets from his supplier. I am being cynical because I keep finding this gap between what you actually need or want and what you are given. Its not a combi is it, they usually get specified as a big as you cen get. You need a boiler that meet your heating load (plus a margin). Find out what that load is an tell the plumbler boiler to suit. I'd be surprised if its anywhere near 28kw, more like 10-14Kw. Then look at arange of makers from the budget end upto the better like Viessmann and seek advice from others on the short list. I'm always suspicious of those who demand only one product but cannot come up with the rationale. You'll end up living with it for the next 10-20 yrs so its worth the effort.

Cheers]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2681#Comment_2681 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2681#Comment_2681 Tue, 01 May 2007 10:08:29 +0100 arthur https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2743#Comment_2743 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2743#Comment_2743 Wed, 02 May 2007 18:22:26 +0100 MarkH https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2744#Comment_2744 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2744#Comment_2744 Wed, 02 May 2007 18:59:44 +0100 Paul in Montreal
For combusion-based boilers, actual efficiency is very much related to duty cycle. Short cycles really hammer the efficiency and oversizing will give much higher fuel consumption than would be the case if the boiler was sized correctly in the first place. Of course, worst case conditions are not usually present so there may be a significant portion of the heating season where the boiler is effectively oversized. A thermal store could help mitigate this in allowing longer (but less frequenty) boiler firings. The thermal store won't change the overall worst-case load though.

Hope this helps,

Paul in Montreal.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2793#Comment_2793 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2793#Comment_2793 Thu, 03 May 2007 19:05:02 +0100 MarkH https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2901#Comment_2901 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2901#Comment_2901 Tue, 08 May 2007 12:35:07 +0100 arthur https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2924#Comment_2924 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=2924#Comment_2924 Tue, 08 May 2007 16:06:00 +0100 LizM https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=3044#Comment_3044 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=3044#Comment_3044 Fri, 11 May 2007 10:20:23 +0100 Guest https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=3058#Comment_3058 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=3058#Comment_3058 Fri, 11 May 2007 13:57:04 +0100 LizM
Again (as previous postings), it looks like you are being told to get a combination boiler which provides both heating and hot water. The high output required is for the instantaneous hot water, not the heating. Go back to whoever is "telling" you to get this boiler and ask what you are getting. If you don't understand, keep asking until you do! If you follow the rule of getting 3 quotes, you will probably get 3 different recommendations.

For clarity, condensing boilers reclaim the heat that is normally lost through the flue gases and so are more effiecient than the non-condensing type. They can be combination boilers, described above, or system boilers which just provide heating directly and can be used to provide hot water via a cylinder.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=9437#Comment_9437 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=105&Focus=9437#Comment_9437 Thu, 15 Nov 2007 00:42:33 +0000 J..M 1. To cater for a up coming extension plan
2. 24Kw was the smallest boiler I could find from that manufacturer with the features I wanted

In fairness to all the stated rating of boilers is the maximum output. The majority if not all boilers can be adjusted to suit your individual requirements, mine is adjustable from 8.8Kw to 24 so in honesty it doesn't have to be like using a thermal lance to heat a cup of coffee ;)

My car has a top speed rating of 135Mph ......... But I don't use all its speed capabilities traversing the Asda car park ;)]]>