boiler stat temperature

alfa beta · 15-01-2011 05:17PM #1

Hi - quick query

Got a firebird condensing oil burner and rad system (2.5k sq foot house with three zones - furthest rads would be abot 30 metres from the burner.)

Just wondering what temp people set the stat on the burner to. Mine is currently around the 65 degree mark (this is what the plumber originally set it to day one).

I feel the house would benefit from a nudge in the upward direction but I just want to make sure I don't do anything stupid by setting that temp too high.

ta.

Sparkpea · 16-01-2011 02:57AM

if you need more heat turn it up

it wont mess anything up

people like different temps.. houses hold the temp better than others sometimes etc. so theres loads of variables as to what other people will have theirs set at - suit yourself

heinbloed · 16-01-2011 10:45AM

Using a condensing boiler which can't condense due to high return temperatures is a rather stupid idea. A cheaper boiler working as efficient as a condensing boiler (return temperature >47 degrees Celsius) would have done the trick as well.
Ask your heating system designer why a condensing boiler was purchased when there was no need for it.

The highest possible surface temperature on the flue-gas exposed side of the heatexchanger (where condensing starts) is for oil
fires 47 degrees Celsius.
If this can't be achieved: no condensing.
Meassure the amount of condensate, compare this volume with the amount of fuel burned and you can check how efficiently the condensing modus is actually used.
In theory for each liter of combusted oil 0.88 liters of condensate can be collected. A system running on 90% fuel efficiency would therefore produce 0.8 liters of condensate.

alfa beta · 16-01-2011 11:31AM

Thanks heinblood - I take it from what you're saying that a condensing boiler would be more suitable with a low temp system like uf heating rather than a standard rad set up.

Out of curiosity is there a way (and a place) to measure the return temp. Or maybe there's a rule of thumb as to what the stat would be set to to achieve a return temp of around 45 (probably not I assume, as I guess it would all depend on distances of piping and effectiveness of pipe insulation etc.)

Still, I'd be interested in playing around with temps and seeing what the most effective way of running the system is - now that it's installed. (Finally .88 litres of condensate sounds high to me, is that figure right.)

Thanks for your reply - very helpful.

Plombier · 16-01-2011 11:34AM

What heinbloed says is absoloutly correct.

I dont understand why SEAI are giving grants to people to change their boilers, in most cases the original system was designed to operate with a flow temperature of 85C and return of 75C the condensing boilers being installed are typically set at 70C flow and 50C return what this effectly does is reduce the output from the radiators by 40% so unless you are going to upgrade some other aspects of the building (insulation) to install a condensing is a waste of money, not to mention the extra CO2 manufacturing the new boiler.

heinbloed · 16-01-2011 12:58PM

Out of curiosity is there a way (and a place) to measure the return temp. Or maybe there's a rule of thumb as to what the stat would be set to to achieve a return temp of around 45 (probably not I assume, as I guess it would all depend on distances of piping and effectiveness of pipe insulation etc.)

Yes, these data can be found with a thermometer. Check the manual of the boiler how to read the return temperature.

If your heating system depends on a higher return temperature switch to natural gas, condensation point at 59.7 degrees Celsius.

But see what you can do with the existing system first, get a heating engineer in to optimise the system, reduce the demand.

yoshytoshy · 16-01-2011 02:09PM

Plombier wrote: »

What heinbloed says is absoloutly correct.

I dont understand why SEAI are giving grants to people to change their boilers, in most cases the original system was designed to operate with a flow temperature of 85C and return of 75C the condensing boilers being installed are typically set at 70C flow and 50C return what this effectly does is reduce the output from the radiators by 40% so unless you are going to upgrade some other aspects of the building (insulation) to install a condensing is a waste of money, not to mention the extra CO2 manufacturing the new boiler.

What heinbloed says is waffle and if you know anything about heating systems you'd know this yourself.

The majority of radiators in houses are oversized ,this is known to be fact. Condense boilers by their very nature are more economical than standard boilers ,regardless of condensing.

This forum will become a joke soon enough ,with the amount of waffle getting spluttered about.

Plombier · 16-01-2011 04:49PM

What heinbloed says is waffle and if you know anything about heating systems you'd know this yourself

About 12% of the potential heat in the combustion is in the form of water vapor. So unless water vapor condenses, giving up its latent heat energy to the boiler water, the maximum efficiency cannot exceed 88%. Obviously to get the efficiency advertised, nearly ALL of the water vapor must condense.

Condensation occurs when the water vapor molecules contact a surface below the dew point around 52C.

If the entering and leaving water temperatures in the boiler are both above the dew point, NO condensation is possible. It doesn’t matter if there are countless water vapor molecules or just one single one.

To increase the efficiency above 88% there must be condensation of water vapor in the flue gas. In order to condense that water vapor, there must be metal temperatures below the dew point. To get that cool metal temperature, colder water must be introduced into the boiler.

The colder the water, the more water vapor is condensed and the higher the efficiency becomes. But it will only begin to condense at the dew point it will need to be a lot cooler to get 93% efficiency.

ANY boiler will be a condensing boiler when you bring cold water into it!

ANY boiler can operate at even 102% efficiency if the water temperature is say 5C.
With that condition, the flue gas can be lower than the incoming air and fuel temperature: thus efficiencies over 100%.

My post is based on these FACTS what have you based your waffle on?

yoshytoshy · 16-01-2011 05:44PM

Plombier wrote: »

My post is based on these FACTS what have you based your waffle on?

Your quoting figures from the internet and theory ,hearsay. I'm putting condensing boilers in every day of the week and they all condense.
I've also had people comment on how much cheaper their bills are since the installation of their condense boiler.

So excuse me if I'm a little annoyed at someone who says "I dont understand why SEAI are giving grants to people to change their boilers"
Some of us earn a living ,trying to do the best for people and work hard at it.
Any respectable installer wouldn't come out with such crazy comments as yourself ,thats a fact.

heinbloed · 16-01-2011 05:44PM

Yoshytoshy wrote:

The majority of radiators in houses are oversized ,this is known to be fact. Condense boilers by their very nature are more economical than standard boilers ,regardless of condensing.

The economics which some plumbers use to educate themself is sometimes shocking....

Under no circumstances a condensing boiler should be used in a non-condensing modus. It is illegal.
The condensing trap MUST be filled AT ALL TIMES.

The flue-balancing would be working at or over it's limits which is very inefficient and reduces the life time of the boiler in itself. Reacting to the fact that the combustion chamber is open when the condensate trap is dry. The boiler is not room-sealed anymore, it is not designed for this purpose.If the boiler's safety functions don't kick in there is a risk of explosion.
And the risk of gas poisoning anyhow, but that price the cowboys would never be made responsible for, lifes can't be replaced.....

At the OP:

Check the competence level of your installer.See yosytoshy's post and ask your questions, like is it efficient to run a condensing boiler in a non-condensing modus and would he recommend it......

And again: read the manual.

And get a CO/natural gas alarm installed straight next to the condensate trap.There are some duds operating out there you never can be sure enough.

yoshytoshy · 16-01-2011 05:49PM

heinbloed wrote: »

The economics which some plumbers use to educate themself is sometimes shocking....

Lord heinbloed ,1000 Points. Internet warrior.

Plombier · 16-01-2011 06:05PM

I'm putting condensing boilers in every day of the week and they all condense

Wow! you have found a way to defy chemistry and thermodynamics of a combustion reaction.

I too install condensing boilers but only in a situation where they are appropriate, in other cases I will advise a customer against changing their boiler because my reputation is more important to me than the money.

yoshytoshy · 16-01-2011 06:09PM

Plombier wrote: »

Wow! you have found a way to defy chemistry and thermodynamics of a combustion reaction.

I rest my case about internet warriors ,no plumber talks like that.

Plombier · 16-01-2011 06:17PM

I am a plumber since 1977 but along the way I have educated myself and I would suggest that you open your mind and do the same just because you think something is correct does not mean it is, please for the sake of your customers buy a book on this subject and read it.

yoshytoshy · 16-01-2011 06:21PM

Plombier wrote: »

I am a plumber since 1977 but along the way I have educated myself and I would suggest that you open your mind and do the same just because you think something is correct does not mean it is, please for the sake of your customers buy a book on this subject and read it.

I'm fully open to anything anyone has to say on this and I know from what you guys are saying ,you're missing several key elements involved in modern condensing boilers and how they operate to maintain condensing while outputing required heat.

Maybe you should read up about what new boilers have to offer.

Plombier · 16-01-2011 06:34PM

Please do explain to me what key elements I am missing, above I have outlined in detail the points I am making, if you have some additional information that you can add then please do.

You can't backup what you are saying and it seems quite obvious that you don't know what you are talking about.

yoshytoshy · 16-01-2011 06:40PM

Plombier wrote: »

You can't backup what you are saying and it seems quite obvious that you don't know what you are talking about.

Seriously ,what is all this backup business ? Heinbloed is the same with his backup thing.

Heinbloed has shown on this forum before that he doesn't know the basics about boilers and has admitted he is not an installer.

You're asking me to backup what I'm saying and all I can say is ,I will have to make a video up of a boiler in operation. Showing flow and return temperatures ,how the boiler copes with rises and how it maintains condensing.

Modulation is the key word here ,modulation.

slavetothegrind · 16-01-2011 06:46PM

Plombier wrote: »

ANY boiler can operate at even 102% efficiency if the water temperature is say 5C.
With that condition, the flue gas can be lower than the incoming air and fuel temperature: thus efficiencies over 100%.

My post is based on these FACTS what have you based your waffle on?

wow, you have beaten the laws of thermodynamics!

Plombier · 16-01-2011 07:58PM

The above efficiency values are based on gross calorific value of the fuel used. Gross calorific value includes the latent heat of water vapour produced during combustion, whereas net calorific value doesn't. Thats why efficiencies of above 100% can be stated.

Modulation controls the output of the boiler to maintain a set temperature it does not modulate the temperature so wrong again.

yoshytoshy · 16-01-2011 08:06PM

Plombier · 16-01-2011 08:22PM

The great question is not whether you have failed, but whether you are content with failure.

Domahony · 01-02-2011 07:38PM

I'm not a plumber or an installer, but I am considering replacing my 20-year old gas boiler with a condensing one and I find this discussion fascinating.

I'd like to extract a few points to test if I am getting this right:

Condensing boilers are more efficient because they take the water returning
from the radiators and pre-heat it using the hot, vapour rich exhaust gases
coming out of the flue. These condense on the return pipes giving up their
latent heat to the water rather than blowing it into the atmosphere.

Heinbloed and Plombier believe that if the return water is at a higher
temperature than the dew point (52 or 47 or 59.7 degrees C), then there will be no condensing and therefore no heat transfer.

They state that most existing home plumbing systems are designed to
have return temperatures of 75 degrees C.

yoshytoshy is installing boilers all the time and sees condensate coming out
of boilers, where the return temperature is higher than those thresholds.

Have I got this right or are there more scientific arguments to be put?

yoshytoshy · 01-02-2011 08:55PM

There will be less condense as the boiler heats ,but the issue I had with this thread and the posts of heinbloed and plombier ,is the issue that non-condensing boilers are more efficient than condense boilers.

This just isn't my experience ,the quality of condense boilers are far more reliable and cleaner than old boilers. The heat from the flue of a condense boiler is not as hot as a non-condensing boiler.

01-02-2011 09:37PM

Domahony wrote: »

I'm not a plumber or an installer, but I am considering replacing my 20-year old gas boiler with a condensing one and I find this discussion fascinating.

I'd like to extract a few points to test if I am getting this right:

Condensing boilers are more efficient because they take the water returning
from the radiators and pre-heat it using the hot, vapour rich exhaust gases
coming out of the flue. These condense on the return pipes giving up their
latent heat to the water rather than blowing it into the atmosphere.

Heinbloed and Plombier believe that if the return water is at a higher
temperature than the dew point (52 or 47 or 59.7 degrees C), then there will be no condensing and therefore no heat transfer.

They state that most existing home plumbing systems are designed to
have return temperatures of 75 degrees C.

yoshytoshy is installing boilers all the time and sees condensate coming out
of boilers, where the return temperature is higher than those thresholds.

Have I got this right or are there more scientific arguments to be put?

You can only fit condensing gas boilers.

esox28 · 01-02-2011 11:09PM

Love it, loveit, loveit,

wot makes me smile:D ??

the battles that we go on with, not the fact we can help the nation 'for free' with our limitless plumbing and heating knowledge and feel good bout it.

love the 'net warrior' so describes most of us:p

esox28 · 01-02-2011 11:42PM

at the tip of blast tube when oil is fired is 1200*c and leaves the flue 'condensing' @ roughly 50*c but on a 'standard' flues leave @ roughly 250*c. wot more is there to say! two heat exchangers v one

boilers over 92% efficiency must be installed as part of new regs. only one way around this...no available connection or area for condensate disposal

never seen an empty condense trap only melted ones due to dodgy plumber not fully tighten then and pre-filling it b4 lighting boiler.

surely the manufacturers know that there boilers are going to be installed into ch systems where boiler will only condense for the initial heat-up period which could be as little as 15 mins and run with a temp differential of 10*c or so for there on.

very interesting point though,
will be contacting our main boiler manu. tomorrow c wot they say bout the trap evaporating.

gas boilers though would be a concern as most are installed inside

Outkast_IRE · 01-02-2011 11:50PM

The condensing boilers are more efficent no argument , im fitting a gas one most weeks and people always find a reduction in their gas bills .
As was mentioned the second heat exchanger alone will provide an increase in efficency over a standard boiler.

heinbloed · 02-02-2011 11:23AM

Domahony asks:

yoshytoshy is installing boilers all the time and sees condensate coming out
of boilers, where the return temperature is higher than those thresholds.

Have I got this right or are there more scientific arguments to be put?

Well, the installer has to have a certain competence.....and off course the specifier as well.

The scientific argument to make use of the condensing modus :

One can't make use of entalphic energy (the energy released whilest condensing vapour/steam) as long as the condensing temperature isn't matched.

If someone who claims the opposite ( claiming to see water driping out of the condensing trap whilest there is no condensing happening) than this is a sure sign that this person either has mental problems/visions or that there is somewhere a leak in the system.

heinbloed · 02-02-2011 11:43AM

Maybe opening a new thread on the issue?

Here a bit more science,
the condensing temperatures of various fuels:

Homeheating oil (light, Kerosene):
Condensing temperature 47 degrees Celsius
amount of condensate when condensing 100% : 0.88 kg water per liter of combusted fuel

Natural gas (low grade)
Condensing temperature 55.1 degrees Celsius
amount of condensate when condensing 100% : 1.53 liter per m3 of combusted fuel

Natural gas (high grade)
Condensing temperature 55.6 degrees Celsius
amount of condensate when condensing 100% : 1.63 liter per m3 combusted fuel

City gas
Condensing temperature 59.5 degrees Celsius : 0.89 liter per m3 combusted fuel

Propane
Condensing temperature 51.4 degrees Celsius

.37 liter per m3
combusted fuel

Butane
Condensing temperature 50.7 degrees Celsius : 4.29 liter per m3
combusted fuel

What are the condensing temperatures of the variuos solid fuels, e.g. coal, lignite, peat, timber ?

02-02-2011 11:58PM

heinbloed wrote: »

Domahony asks:

Well, the installer has to have a certain competence.....and off course the specifier as well.

The scientific argument to make use of the condensing modus :

One can't make use of entalphic energy (the energy released whilest condensing vapour/steam) as long as the condensing temperature isn't matched.

If someone who claims the opposite ( claiming to see water driping out of the condensing trap whilest there is no condensing happening) than this is a sure sign that this person either has mental problems/visions or that there is somewhere a leak in the system.

How many boilers have you worked on/repaired to decide what's right and what's wrong in the boiler world, I know why condense is coming out of the boiler, but It's a shame you can't take someones word for it, I'll leave you to your books.

Billy Bunting · 03-02-2011 12:55AM

alfa beta wrote: »

Hi - quick query

Got a firebird condensing oil burner and rad system (2.5k sq foot house with three zones - furthest rads would be abot 30 metres from the burner.)

Just wondering what temp people set the stat on the burner to. Mine is currently around the 65 degree mark (this is what the plumber originally set it to day one).

I feel the house would benefit from a nudge in the upward direction but I just want to make sure I don't do anything stupid by setting that temp too high.

ta.

Adjust the thermostat when you need to, the thermostat will control the temperature of the water in the radiators,the hotter the radiators the quicker the house will heat, too low and you will begin to feel it.

boiler stat temperature

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