Boiler Sizing
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Spent a few hours measuring everything this afternoon and inputted all the data as best I could and it spat out 13.2Kw. Almost exactly what Muggles predicted. I am shocked. Its a large house which is not the most energy efficient and this is at the lower end of the boiler output range for nearly all models.
I dont think it makes a difference to the output figure but i used 45' for the UFH flow temps and 70' for the rads. Is that correct? If so it seemed to indicate the selected rad sizes using the online calculators were correct.
Assuming all the measurements are correctly inputted are there any variables that could throw the calculations out?
I dont think it makes a difference to the output figure but i used 45' for the UFH flow temps and 70' for the rads. Is that correct? If so it seemed to indicate the selected rad sizes using the online calculators were correct.
Assuming all the measurements are correctly inputted are there any variables that could throw the calculations out?
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I don't run my heating 24/7, it switches off at night, and when we go out, the 18 kW boiler is ample to maintain the temperature in a three story house, but it is the time to re-heat from cold or an eco temperature.
My way around it is to heat rooms with a delay for some rooms, but this means larger radiators able to put that heat into the rooms, and clearly my radiators are not big enough, as the boiler can be heard cycling.
My way around it is to heat rooms with a delay for some rooms, but this means larger radiators able to put that heat into the rooms, and clearly my radiators are not big enough, as the boiler can be heard cycling.
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Personally, I'd go with something you can take advantage of the opentherm output of the nest with. This will provide better control and more efficient heating, especially as you should have low temperature heating set up to keep the boiler in condensing mode as much as possible.
You will need to put the hot water on a hot water priority system though.
There is also a lot of professional members on here who don't rate the Worcester boilers that highly in terms of build quality. The advice is don't take which? Magazine results as gospel.
I'm sure the guys on the forum will advise what boilers the opentherm will work with,
Off the top of my head
Intergas xclusive 24 (can be set as 18kw heat only)
Atag i15s or i18s (they do a 15kw and an 18kw). I know they work well with opentherm aswell, and can be extended upto 14 years warranty. I know of people that have had these fitted for 3 years and not had any issues thus far, they are also well liked on home automation forum.
Possibly vokera (Vulcan continental might be able to advise a model)
You will need to put the hot water on a hot water priority system though.
There is also a lot of professional members on here who don't rate the Worcester boilers that highly in terms of build quality. The advice is don't take which? Magazine results as gospel.
I'm sure the guys on the forum will advise what boilers the opentherm will work with,
Off the top of my head
Intergas xclusive 24 (can be set as 18kw heat only)
Atag i15s or i18s (they do a 15kw and an 18kw). I know they work well with opentherm aswell, and can be extended upto 14 years warranty. I know of people that have had these fitted for 3 years and not had any issues thus far, they are also well liked on home automation forum.
Possibly vokera (Vulcan continental might be able to advise a model)
When i did this sizing survey it gave me 26Kw. Now i am very confused
Pleased you made the effort to do a proper calculation.
I don't worry too much about boiler modulation as long as it's above 1:5. Out of interest it's easy with Heat engineer to change the external design temperatures; change it from -3 or -5 to +9 or +10 degrees and see the loss then, that will give you a minimum input in milder weather when you still need heating.
If you want to get more info try to attend a Heating Efficiency and Optimisation webinar, I don't have dates but the schedule is at www.vokera.co.uk/webinars. Not sure if there's one in December though (you don't have to be Gas safe).
I work for a manufacturer so do not feel these forums are for advertising, suffice to say I do not get problems with our boilers but then I install and service the boilers properly.
FYI radiator outputs are certified at 75C flow (65 return)
I like OpenTherm controls and EPH (not great looking but DHW can be OT controlled as well as the heating) ours can do it but too much faffing around in parameters though new gear coming soon. I connect an external sensor too but not all boiler/controls permit this
My preference is a comfort temperature and a setback temperature not ON/OFF.
I don't worry too much about boiler modulation as long as it's above 1:5. Out of interest it's easy with Heat engineer to change the external design temperatures; change it from -3 or -5 to +9 or +10 degrees and see the loss then, that will give you a minimum input in milder weather when you still need heating.
If you want to get more info try to attend a Heating Efficiency and Optimisation webinar, I don't have dates but the schedule is at www.vokera.co.uk/webinars. Not sure if there's one in December though (you don't have to be Gas safe).
I work for a manufacturer so do not feel these forums are for advertising, suffice to say I do not get problems with our boilers but then I install and service the boilers properly.
FYI radiator outputs are certified at 75C flow (65 return)
I like OpenTherm controls and EPH (not great looking but DHW can be OT controlled as well as the heating) ours can do it but too much faffing around in parameters though new gear coming soon. I connect an external sensor too but not all boiler/controls permit this
My preference is a comfort temperature and a setback temperature not ON/OFF.
Thanks everyone for the help.
Vulcan - On the basis of 13.2Kw being the requirement that the Heating Engineer software spat out do i just go for a 15Kw model (if 12Kw is the one below) and it just doesnt work to full capacity or an 18Kw version. I dont understand how the efficiency ratio works to select the correct size accross the various manufacturers as i see they dont all do a 13.5Kw unit. I need an output range to work to or do i just go for the nearest size over 13.5Kw?
Vulcan - On the basis of 13.2Kw being the requirement that the Heating Engineer software spat out do i just go for a 15Kw model (if 12Kw is the one below) and it just doesnt work to full capacity or an 18Kw version. I dont understand how the efficiency ratio works to select the correct size accross the various manufacturers as i see they dont all do a 13.5Kw unit. I need an output range to work to or do i just go for the nearest size over 13.5Kw?
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I'd ask the installer for his advise.
Theory is great, reality doesn't always match. Also asking some technical stuff to the installer will give you an idea if he is a muppet or not and also tell him that you are not also, a muppet....
I'd also get several opinions from various installers.
Are you remembering that your calcs are net values not gross and that boiler ratings might be gross, so lossess,etc should be factored in?
Firm up your thoughts and show them to your boiler engineer
I wouldn't worry about being over by much, recent test determined for max appliance efficiency a factor of 1 or even 0.75 is best.
The object of the excercise is comfort and although perfect or undersized boilers has best potential heat in to heat into system water, under certain circumstances comfort wasn't achieved in time.
As long as the burn time is longer than 3 minutes the efficiency hit is 1%.
A 20 will modulate to 3.5kW and at 9⁰C outside you'll need more than that.
At the risk of advertising search boiler baggage on YouTube for pointers on boilers. All brands tell you they're the best, it's what they're not telling you that's important including any Cashback or points awarded for the installer.
The object of the excercise is comfort and although perfect or undersized boilers has best potential heat in to heat into system water, under certain circumstances comfort wasn't achieved in time.
As long as the burn time is longer than 3 minutes the efficiency hit is 1%.
A 20 will modulate to 3.5kW and at 9⁰C outside you'll need more than that.
At the risk of advertising search boiler baggage on YouTube for pointers on boilers. All brands tell you they're the best, it's what they're not telling you that's important including any Cashback or points awarded for the installer.
Damn I love being right
Yes the WB 4000 15kW or Viessmann 200-W 19kW would be good options. They both modulate well, so they'll not only be efficient on the very coldest days but also on milder days. A heat loss of 13.2kW when it's -3°C outside translates to 6.1kW when it's 9°C outside, as heat loss is a function of the difference between indoor and outdoor temperatures
Yes the WB 4000 15kW or Viessmann 200-W 19kW would be good options. They both modulate well, so they'll not only be efficient on the very coldest days but also on milder days. A heat loss of 13.2kW when it's -3°C outside translates to 6.1kW when it's 9°C outside, as heat loss is a function of the difference between indoor and outdoor temperatures
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