Condensing boiler with Radiators

arghh

At this moment and time I am thinking of having a condensing boiler with radiators to heat the house. What I want to find out is has anyone else gone down this route and how is it working out. Condensing boilers seems to be very good with ufh but how do they work out with radiators. Any feedback will be appreciated

JamesM

arghh wrote:

At this moment and time I am thinking of having a condensing boiler with radiators to heat the house. What I want to find out is has anyone else gone down this route and how is it working out. Condensing boilers seems to be very good with ufh but how do they work out with radiators. Any feedback will be appreciated

As far as I know, condensing boilers would normally be matched with standard radiators.
They can be run at low temperatures, so are also suitable for UFH.
Jim.

GreeBo

From what I know a condensing boiler is really only working in condensing mode (and thus being extra efficient) when it is run a lower temperatures.
This makes it (in my opinion) unsuitable for regular radiators.

Get the highest rated non-condensing boiler and you will be fine.

arghh

I have not seen any posts or heard of anyone who has a condensing boiler with radiators.The only info I have seen is from the SEDBUK which I got a link to Grant Engineering which said that you could use normal Rads. I am just hoping that someone has gone down this route and can give me the pros and cons of having a condesing boiler.

GreeBo

Well the pro are that they are more efficient
The con is that they are only more efficient when they are actually running in condensing mode and this only happens at lower temperatures.

This makes them more suitable for UFH where they are on all day at a comparably lower temperature than normal rads are.

arghh

as Fagan in Oliver would say I have to think it out again

JamesM

GreeBo wrote:

Well the pro are that they are more efficient
The con is that they are only more efficient when they are actually running in condensing mode and this only happens at lower temperatures.

I believe that this is not true. The heat exchanger in a condensing boiler extracts more heat from the gasses than a conventional boiler, and is about 10% more efficient, no matter whether you use rads or underfloor. A conventional boiler has to have a certain flue temperature, so that the gasses will not condense in the boiler and corrode the boiler. The condensing boiler is made of stainless steel, so that the corrosive gasses can condense in the boiler without causing damage. There is a drain to take away the water which condenses in the boiler. Running a conventional boiler at the low temperature suitable for underfloor heating will damage the boiler. So, yes a condensing boiler which can be run at a low temperature is more suitable for underfloor heating, but is also more efficient than a conventional boiler when used with radiators.
It is up to someone to decide whether the extra cost of a condensing boiler is worth the extra efficiency.
Jim.

GreeBo

JamesM wrote:

I believe that this is not true. The heat exchanger in a condensing boiler extracts more heat from the gasses than a conventional boiler, and is about 10% more efficient, no matter whether you use rads or underfloor. A conventional boiler has to have a certain flue temperature, so that the gasses will not condense in the boiler and corrode the boiler. The condensing boiler is made of stainless steel, so that the corrosive gasses can condense in the boiler without causing damage. There is a drain to take away the water which condenses in the boiler. Running a conventional boiler at the low temperature suitable for underfloor heating will damage the boiler. So, yes a condensing boiler which can be run at a low temperature is more suitable for underfloor heating, but is also more efficient than a conventional boiler when used with radiators.
It is up to someone to decide whether the extra cost of a condensing boiler is worth the extra efficiency.
Jim.

Actually, you are correct.:o
I guess the ratings have changed a bit since I last looked.

Highest Sedbuk rating for a condensing boiler is 91.5%
For a non condensing its 82.1%

Regarding running temps:
Return temp to the boiler needs to be below 57C so that it can be used to condense the flue gases. A return temp above 57C means the boiler will not be working in condensing mode and will be less efficient.

UFH is ideal for a condensing boiler. When using radiators you need to oversize them so that you can run a lower supply temp so that the return temp is below 57c. Many retrofit condensing boilers will rarely condense as the boilers will be sized for higher flow temps. Reducing the flow temp will prevent them from heating the room adequately.

JamesM

GreeBo wrote:

Actually, you are correct.:o
I guess the ratings have changed a bit since I last looked.

Highest Sedbuk rating for a condensing boiler is 91.5%
For a non condensing its 82.1%

Regarding running temps:
Return temp to the boiler needs to be below 57C so that it can be used to condense the flue gases. A return temp above 57C means the boiler will not be working in condensing mode and will be less efficient.

UFH is ideal for a condensing boiler. When using radiators you need to oversize them so that you can run a lower supply temp so that the return temp is below 57c. Many retrofit condensing boilers will rarely condense as the boilers will be sized for higher flow temps. Reducing the flow temp will prevent them from heating the room adequately.

I am only beginning to figure out how these things work
I have noticed with the more recent conventional boilers that, if they connect to an existing chimney or have a long, high, flue, they are so efficient that, very often, the gasses condense anyway and water drips down the flue and out any cracks it can find. That would be with the boiler stat set at, say 60c. So, with a condensing boiler, where the flue temp is below that of a conventional one, and with the flow at 60c, the return should be below 57c, therefore quite a bit of condensing will take place. I have heard people with new condensing boilers and radiators, say that the flow of condensate from the plastic pipe is like a river. As you say, the lower the temp, the more efficient the boiler. For much of the year, people will not have their boiler stats set above 60c. In fact people say that they have to turn off their heating, because the house gets too hot much of the time. There are times when you just want to warm up the house a bit on a spring or autmn evening. Now with condensing boilers, you can just lower the temp below 60c. This was not recomended before now because of the damage from condensation to convential boilers.
Jim.

arghh

Appeciate all the info guys will be armed with more details when I am purchasing the boiler. Sourcing the right heatsource and the right insulation are the biggest drag since I started and going down the renewable energy route is confusing and expensive. As the saying goes "beware of hippies with checkbooks":D

Just came upon this link https://www.rvr.ie/default.aspx?subj=news/NewsArticleList

Viking House

We normally fit Condensing Combi boilers that don't need a tank in the attic or a copper cylinder. They are 30% more efficient than the copper cylinder systems because you are not keeping a copper cylinder of water hot all day you just heat what you need. We bought the last few in B+Q for about €900.

GreeBo

Viking House wrote:

We normally fit Condensing Combi boilers that don't need a tank in the attic or a copper cylinder. They are 30% more efficient than the copper cylinder systems because you are not keeping a copper cylinder of water hot all day you just heat what you need. We bought the last few in B+Q for about €900.

but arent there issues with a sudden high demand for lots of hot water?
( a few showers, baths, waship up etc?)
Also dont they get Hot tap pressure purely from the mains?

Do-more

You could consider using fan coils such as these as they can run on 45 degree water and so you are guaranteed that your boiler will run fully condensing. Also much more efficent than UFH IMO. I spoke to them recently and they have a demo house in Cork for prospective customers and also provide free training sessions for plumbers. Haven't got down for a look yet, but hope to do so soon.

ednwireland

watch yourself with sedbuk ratings they specifically dont allow non condensing boilers to be rated at more than 85.7% efficient even if they are here is an expanation i got from an engineer at grants

"Difference between GROSS/NETT and SEASONAL EFFICIENCY

There are two different systems of determining a rated boiler efficiency, Gross and nett which used in Ireland and most of Europe excluding the UK and seasonal efficiencies which is used in the UK. On our brochures we claim 95% nett. which is correct, however the same boiler sold in the UK would be 85.7 seasonal efficient. This is where the difference is. Below is a further explanation of efficiencies.

Gross or nett efficiencies

Gross or nett efficiencies refer to an efficiency calculated using either the gross or nett calorific values of the fuel. Gross Calorific Value is the maximum heat in the fuel, including the latent heat, released during the combustion process. Nett Calorific Value is the gross calorific value, less the latent heat produced. The latent heat converts the water produced during the combustion process into steam. This heat is normally lost with the combustion gasses through the flue system. An efficiency calculated ignoring the latent heat, i.e. using the nett CV will always be greater than one where the latent heat is included, ie. using the gross CV. Therefore, the so called ‘nett efficiency’ will be higher than the ‘gross efficiency’. All boiler tests in Europe use the ‘nett efficiency’ method for calculating appliance operating efficiency!

Seasonal Efficiency

The UK use a different system of determining the boiler performance which is based on the seasonal efficiency of the boiler, this is called SEDBUK

SEDBUK is the average annual efficiency achieved in typical domestic conditions, making reasonable assumptions about pattern of usage, climate, control, and other influences. It is calculated from the results of standard laboratory tests together with other important factors such as boiler type, ignition arrangement, internal store size, fuel used, and knowledge of the UK climate and typical domestic usage patterns.

Note; When calculating the seasonal efficiency of a standard oil boiler the part and full load are used in the calculation, however they are capped at 91% and 92 % respectively, so no standard boiler can achieve a seasonal efficiency above 85.7% hence the large difference in the two figures."


i asked the question because the sedbuk rating was giving me 12% extra efficiency weras the gross was about 2% so i bought a non condensing boiler because i read a couple of papers stating that if your water return temp is too high you lose the condensing bit of your boiler.

hope that helps

Viking House

GreeBo wrote:

but arent there issues with a sudden high demand for lots of hot water?
( a few showers, baths, waship up etc?)
Also dont they get Hot tap pressure purely from the mains?

No problem with high demands for water, you can fill 20 baths of hot water with a Combi, mains pressure is quite good also a lot better normally than the pressure you get from the tank in the attic.