Size of New Boiler?

Aeneas

I am thinking of replacing my old oil fired boiler with a new condensing one. The house is approx 1900 sq ft and the system needs to support 15 radiators, five or six of which are double rads. What size (BTU) boiler will I need? And what is the best condensing boiler?

Joey the lips

You need to calculate the BTU requirements for each room

http://www.waterfordstanley.com/1331.htm

Here is a link to a site that will help you. When you have each rooms btu calculated add them all up you add 20000 btus for hot water. That will give you the size of the boiler needed.

although 14 rads I imagine your figures come out around 120 -140 000 BTU.

Work it out. There is a lot of assumptions here, First of all if you need a new boiler the system is prob old which means the rads wont operate as well. I would read up on condensing boilers before I consider this. A condensing boiler does not raise the temp as high as the trad boiler so usually bigger rads are needed but I am sure you will get a lot more opinion on this here

joeduggan

Aeneas wrote: »

I am thinking of replacing my old oil fired boiler with a new condensing one. The house is approx 1900 sq ft and the system needs to support 15 radiators, five or six of which are double rads. What size (BTU) boiler will I need? And what is the best condensing boiler?

if u are just changing ur boiler, go around and measure the rads and state whether thy aare double or single panel. then bring the measuements to ur local plumbing shop where they will calculate the amount of btus the new boiler should have.

Joey the lips

joeduggan wrote: »

if u are just changing ur boiler, go around and measure the rads and state whether thy aare double or single panel. then bring the measuements to ur local plumbing shop where they will calculate the amount of btus the new boiler should have.

I agree joe but some plumbing providers are lazy sh1ts and even today wont do this. Its no harm in you knowing the size of the boiler you need based on the house size. There is also the possibility that the rads were under/over specified or are the old long single panel type.

I find its better to work out your own requirements. If your worried air on the side of caution and over spec.

A last option is to take the plate from the boiler ring the manufactur and they will tell you the size

Aeneas

Joey the lips wrote: »

You need to calculate the BTU requirements for each room

http://www.waterfordstanley.com/1331.htm

Here is a link to a site that will help you. When you have each rooms btu calculated add them all up you add 20000 btus for hot water. That will give you the size of the boiler needed.

although 14 rads I imagine your figures come out around 120 -140 000 BTU.

Work it out. There is a lot of assumptions here, First of all if you need a new boiler the system is prob old which means the rads wont operate as well. I would read up on condensing boilers before I consider this. A condensing boiler does not raise the temp as high as the trad boiler so usually bigger rads are needed but I am sure you will get a lot more opinion on this here

Thanks. Internal floor space is 1828 sq ft. Multiplied by ceiling height (8ft) gives 14624 cu ft. Multiplied by Stanley's recommended factor of 7 (most of the living areas are north facing, some of the walls are solid concrete, some insulated cavity, some hollow block) gives 102,368 btus. Plus 20,000 for hot water. Total 122,368.So, pretty much as you suggested.
Rads were put in ten years ago and look pretty similar to the ones available today, fins at back, grills at top etc.
This calculation would suggest a 35kw boiler. I am looking at a Firebird Enrironmax Heatpak. They have 35kw boilers. But maybe I should go for a 44kw to be on the safe side?

Joey the lips

Aeneas wrote: »

Thanks. Internal floor space is 1828 sq ft. Multiplied by ceiling height (8ft) gives 14624 cu ft. Multiplied by Stanley's recommended factor of 7 (most of the living areas are north facing, some of the walls are solid concrete, some insulated cavity, some hollow block) gives 102,368 btus. Plus 20,000 for hot water. Total 122,368.So, pretty much as you suggested.
Rads were put in ten years ago and look pretty similar to the ones available today, fins at back, grills at top etc.
This calculation would suggest a 35kw boiler. I am looking at a Firebird Enrironmax Heatpak. They have 35kw boilers. But maybe I should go for a 44kw to be on the safe side?

Great boiler. Give there techanical dept a buzz they are very helpful. Shelia usually answers the phone in sales. Tell her that a plumber said she was the soundest lady in cork and she would steer you right! She will tell you what one to go for. My attitude is for a 100 euro price difference its not worth the risk.

I cant remember how the grant situation is now are you not entitled to a grant for a condmnsing boiler,

Lastly, you will need a new flu. They are not interchangable.

Micky Dolenz

I would recommend you powerflush system before installing new boiler, the new heat exchager will not like the grime of an old system.

It's best to undersize boiler, this will ensure it stays condensing for as long as possible, while the boiler condenses it is 90% + efficient, which means, of the 100% energy used to burn the fuel, 90% of it is utilised. When the boiler is not condensing it's efficiency is that of a standard boiler, around 80%.

The boiler, while condensing can give off surface rad tempertures of approx 65D, this is very hot. As long as the return water is about 55D the boiler will remain condensing and in high efficiency mode.

Powerflush,balance and chemically treat system.

Joey the lips

Micky Dolenz wrote: »

I would recommend you powerflush system before installing new boiler, the new heat exchager will not like the grime of an old system.

It's best to undersize boiler, this will ensure it stays condensing for as long as possible, while the boiler condenses it is 90% + efficient, which means, of the 100% energy used to burn the fuel, 90% of it is utilised. When the boiler is not condensing it's efficiency is that of a standard boiler, around 80%.

The boiler, while condensing can give off surface rad tempertures of approx 65D, this is very hot. As long as the return water is about 55D the boiler will remain condensing and in high efficiency mode.

Powerflush,balance and chemically treat system.

Folks! We are in the presence of the great one

Micky Dolenz

Micky Dolenz wrote: »

The boiler, while condensing can give off surface rad tempertures of approx 65D, .

Hi, Micky, I have yet to come across the holy grail of heating systems like the one you have described:D, i would be interested to know about hot water performance on this kind of set up, cheers Gary.

Joey the lips

It is only possible for a condensing boiler to work to these very high efficiencies if the flow and return pipework is also kept below 55°C. The flow & return temperatures need to be maintained for the heat transference to occur from the flue to the water (i.e. heat transference goes from hotter to cooler materials).

Whats 10oC! i caught the jist anyhow!

http://www.condensingboiler.org.uk/

Morning Joey, i get yea, but I'm interested(without sounding like a smart ass) in the undersizing of the boiler and the effect on reheat times of a cylinder, the effect on the water at the tap and also would the system have hot water Priority, if not would the cylinder once satisfied effect the return temp on the boiler, Just out of interest,:) Gary

Joey the lips

Understood. I have sold condensing boilers but TBH at the moment plumbers seemed focused on the Combi type boiler. I am not totally proficcient with the condensing only boiler. In fact knowlege collected to date has led me to believe that is a bit of a holy grail.

The problem is that all the oil boilers are solidly condensing and thats the biggest area of sales for firebird and was for gerkross so even if in the morning you decide feck it I am not going to go condensing oil. Your choice will be short lived cause that is all that is available in oil.

I understood the explination of making it work harder although this is not a logic i am use to. My logic on the traditional set up is over spec. It allows for expansion. However the "New" Logic on condensing seems to be underspec as it causes the condensing to kick in more quickly and for longer.

I am still a little green in the area and shall be as the biggest area of sales and fitting at the moment is not heating but bathrooms and general plumbing.

I look at a lot of installations and have yet to come a cross a installation that has made full use of a condensing boilers advantages, so I'm always interested in how others have done it, you can never have to much information:D, Gary.

OP, sorry for stealing your tread I'll leave it alone now:o

Joey the lips

gary71 wrote: »

I look at a lot of installations and have yet to come a cross a installation that has made full use of a condensing boilers advantages, so I'm always interested in how others have done it, you can never have to much information:D, Gary.

OP, sorry for stealing your tread I'll leave it alone now:o

Understood and agree. On the OP. I would suggest that the op tell the sales person his btu calculation and simply ask is it better to overspec the boiler as was traditional or will slightly underspecing tend to bring out better performance. Bear in mind to tell the person that you already have the rads installed as I see a new generation of sales people discussing using bigger rads with condensing boilers.

Micky Dolenz

gary71 wrote: »

Hi, Micky, I have yet to come across the holy grail of heating systems like the one you have described:D, i would be interested to know about hot water performance on this kind of set up, cheers Gary.

It's not as unrealistic as you would think.
Two things are very important, ( even If you don't have weather compensators and modulating burner)


one is power flush the old system, because sludge and grim absorbs heat, the boiler has to reach higher tempertures to achieve a suitable surface to air temperture. So less sludge means better transfer of heat.

second, is education of the end user of the product. inform of the need to keep boiler as low as possible, i recommend 65D flow temp, the return will still be under dew pt and surface temps are comfortable. If it slightly passes dew pt on occasion, it's not too much of a problem as the boiler will be condensing for a large percentage of the time hence saving.

If flow temp is 65d at flow on cylinder, you can expect plumbing hot water to be in the mid to high 50's, as we know the regs state that hot water should be no higher than 60D, i belive it is in the gas regs too IS: 813.

All in all, condensing boilers are a great step forward for heating, They will save money even if they are not always in condensing mode. the technology can only get better between controls and modulating units.

In keeping with the original OP's question, regards to the boiler sizing, would you size it for rads and cylinder or rads only with hot water priority, i am interested as it's always good to know how well a design works, so I'm not talking out of my backside when asked my opinion. I would go with the priority hot water, i could see that working real well if the reheat times were OK, Cheers, Gary


OP, if you look at the Sedbuk list: http://www.sedbuk.com/ you can choose from the most efficient boilers, if you don't take Micky's good advise then take off 4-5% off the efficiency rating of a condensing boiler as they will only condense on start up.

Carlow52

Micky Dolenz wrote: »

... as we know the regs state that hot water should be no higher than 60D, i belive it is in the gas regs too IS: 813.

no higher than
or
not less than

Micky Dolenz

Carlow52 wrote: »

no higher than
or
not less than

Your doubley confused?

I meant it as I wrote it,. But for your peace of mind here are more details.

IS: 813
8.7.5 - On Commissioning, the discharge temperture of hot water for domestic purposes shall be controlled at or below 60C.

If your worried about Legionella keep your hot water over 50C and your cold water under 20C. Otherwise fit a scald or thermostatic mixer valve after the cylinder.

Hope that clears it up for you.

Fishtits

Layman here, (in plumber terms) after extensive research, opted to fit a Firebird condensing boiler to a 30 yr old system.

Fired it up and it condensed straight off, got a plumber mate to come over and tweak the system, no big changes, just peace of mind.

Gone from 2,500 litres to 1,500 kerosene consumption PA. It will pay for itself within three years.

Far cry from the 15 year payback on solar panels...

No brainer IMHO.

JamesM

Fishtits wrote: »

Layman here, (in plumber terms) after extensive research, opted to fit a Firebird condensing boiler to a 30 yr old system.

Fired it up and it condensed straight off, got a plumber mate to come over and tweak the system, no big changes, just peace of mind.

Gone from 2,500 litres to 1,500 kerosene consumption PA. It will pay for itself within three years.

Far cry from the 15 year payback on solar panels...

No brainer IMHO.

Actually any modern boiler compared to a 30 year old boiler could bring your consumption from 2,500 litres to 1500 litres PA.
Also any modern boiler starting from cold will "condense straight off".
And, to be honest, fitting a condensing boiler to a system that was not designed for it, will not be much more efficient than a standard modern boiler.

Having said all that, you are probably wise to go for a condensing boiler when you are replacing
Jim.