Please recommend a new condensing boiler

[bixfoo]

Folks,

Looking to replace boiler - Ideal Concord WRS255A 16kW from prehistoric times. All of my research suggests that this is nightmarishly inefficient.

House is four bed detatched, boiler is in the garage.

I'm guessing that the current Y plan heating system can remain, and I can just get the boiler replaced?

Be interested in any recommendations you learned folks might have on a suitable replacement condensing boiler. I don't want a combi boiler.

Any approximate indication of cost of boiler + fitting appreciated i.e. to nearest £500.


Thanks,
Bixfoo

 

[croydoncorgi]

If you keep existing Y plan and rads, etc. do NOT assume that your shiny new condensing boiler will condense much.

Publicity that states that a condensing boiler is (eg.) 92% efficient at converting gas energy to hot water is usually very misleading. To achieve maximum efficiency the boiler Return water MUST be below 56 degrees. On most existing conventional heating systems, this will hardly ever be achieved.

Ideally, your first step should be to measure what temperature your boiler return pipe runs at with the current setup and then decide whether you need to redesign or not.

 

[Rob]

doesnt the 55*C return temp reffer to the original condensers with the two HE.

thought this was why they introduced pre-mix? anyone...?

 

[meldrew's_mate]

CroydonCorgi is right, full efficiency is not achieved unless the return water is 56 C or less, however band A condensing boilers are usually well over 85%.....but we're getting off the point.

You can keep the existing Y plan configuration, but you must have TRVs on ALL rads except in the room with the roomstat. To aid efficiency you may wish to consider increasing the size of some old rads to give cooler return temperatures. An auto by-pass valve is also a good idea with so many TRVs, from your description of house a 55,000 btu/hr boiler would probably only be large enough to heat a well insulated 4 bed house (post 1980's I'd guess), so here's my recommendation (remember, opinions vary) try the Ideal icos HE18, it's quiet, it's made in Britain, and reliable (so long as it is installed on a properly cleaned system!!)

Costs vary greatly too, according to present configuration, gas supply suitability (if it's undersized that'll have to be put right), electrical work (most new boilers need a permanent supply + switched live), location, and supplier (for BG add £600 to £800 !!). I would expect it to be in the region of £2000.

The cooler the flow temperature the more likely the boiler is to have return temps below 56C, so setting the flow to about 65C will allow DHW generation with maximum condensing. Most heating is designed around 75C flow temperatures, with -1C outside temps, so it's easy to see that for 350 days of the year flow temperatures do not need to be so high to get adequate heating by reducing it to 65C.

 

[Gasguru]

The dew point is around 55-56 centigrade - it does vary slightly (but only a 1 or 2 points) between the different burner types and for maximum condensing the dew point should be as high as possible.

To get the highest efficiency use a weather compensation sensor (and set it up correctly) or with a non-weather ccompensation boiler run the heating flow temperature at the boiler as low as posible that will adequately heat the property. (it will only need to be on max when its snowing!)

Pre-mix burners were introduced as a method to reduce NOx emissions. You will see boilers with this type of burner are rated as Class 5 emissions. The nitrogen oxides are significantly lower. In many areas of Europe it is mandatory to use Class 5 emission boilers.

As an interim Glowworm produced a water cooled burner - this was another way of reducing emmsisions - from what I hear the boiler costs a fortune in spares and was not particularly reliable boiler.

You will notice the small flame size and hence lower flame temperature on pre-mix burners. NOx are formed at high flame temperatures by nitrogen reacting with the combustion products leading to smog/acid rain etc.

In the automotive world older vehicles fed exhaust products back into the intake manifold; again to reduce the flame temperature during combustion and lower NOx. In modern cars the catylitic converter converts the NOx back to harmless nitrogen and oxygen.

 

[croydoncorgi]

The Glow-worm water-cooled burner, such as used on the Energysaver 40 etc., seemed to work OK. The problems were elsewhere, principally IMHO due to the 'open-plan' design. This allowed moist air at low-ish temperatures to circulate around inside the boiler and (in particular) pass through the fan. As a result, the one I scrapped about 6 months ago was in a very messy state, with a lot of corrosion. There was also a condensate leak from the back of the open tray (!!) under the secondary heat exchanger. To fix it would have meant removing the HX, with LOTS of corroded screws, etc. So: in the skip!

Also IMHO, a pre-mix burner is a must-have for a condensing boiler. It gives better control of gas mix, especially when modulated down, and also puts the fan well upstream of hot and potentially-wet flue gas.

 

[bixfoo]

Thanks for all the help guys. I'll look round for some quotes.


Thanks again,
Bixfoo