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Central Heating

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Misky | 13:52 Mon 18th Jan 2021 | Home & Garden
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Hi, we're just getting used to our heating system, having had a coke fire with a back boiler since we moved in about thirty years ago. In October 2019 (so this is our second Winter) we had a new boiler installed, and a log burner replaced the coke fire. All was well last Winter, but this Winter, unless the log burner's going, the heating in the house doesn't get past 19 degrees although we set it for 22. Will this be a problem with the boiler, or do you think we might simply need new radiators throughout? The radiators are older than thirty years too.

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When you design a central heating system you assume an outside temperature of zero, decide a temperature you want each room to be then calculate the heat-loss through the walls and windows to decide the rate of heat required in each room assuming a particular boiler temperature and what size radiators you need. Add them all together and you get the size of...
14:20 Mon 18th Jan 2021
When you had your boiler installed, was the system flushed and inhibitor put in? When your heating is on are the radiators the same temperature at top and bottom?
Alternatively they may just need bleeding.
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Hi Tony, yes, apparently they did all that flushing and stuff. We bled the radiators in October just gone, and they're the same top and bottom.
In that case, try upping the boiler temperature a bit. Reflectors behind any radiators on outside walls might help as well.
Question Author
Thanks BHG I'll try that. I thought that putting the boiler temp up would just mean it working harder to try and get to a temperature it can't reach (in that, if it can't reach 22 it won't reach 25 either), but I'll try.
When you design a central heating system you assume an outside temperature of zero, decide a temperature you want each room to be then calculate the heat-loss through the walls and windows to decide the rate of heat required in each room assuming a particular boiler temperature and what size radiators you need. Add them all together and you get the size of boiler you need to supply that heat. If it's particularly cold outside the heat-loss might be greater than that used in the design calculations and upping the boiler temperature will help.
In the worst case (for you) the designer might have assumed you would also be using the wood-burner so the boiler alone will not be powerful enough to supply enough heat to service the house.
Putting reflectors behind the radiators helps to keep the heat inside the house rather than it being radiated through the walls to the outside.
Question Author
Thanks again bhg. That makes perfect sense. The burner wasn't in place when we had the boiler installed - we had taken out the coke fire and back boiler to replace it with the gas ch but we missed the real flames and sweltering heat in the living room so had the burner installed later. I'll do as you say now and hope it works.
Incidentally, if you have inhibitor in you system you should never need to bleed your radiators. The gas in radiators is hydrogen, generated by the steel radiators being slowly corroded. I put Fernox in my system and it hasn't needed bleeding in 25 years.
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Oh, well that's worth knowing too - thank you!
Why do you need a log burner as well as central heating? If you dont mind me asking, we have fires but never use them because we use the central heating, obviously we have fire serviced as well as the boiler on a yearly basis, I regularly bleed the radiators just for piece of mind really!
Add on to my post.
Put that insulating foil behind your radiators, particularly those on outside walls, I have done this with foil you can get on a roll with a foam backing, this helps.
That's what I meant by "reflectors" joe. I'm mean, so I used kitchen foil on cardboard rescued from large boxes which works very well.
I tried that but found the cardboard kept coming away from the wall, or the foil kept curling up, thats why I decided to buy the roll from screwfix i think, Im not calling you mean, Im all for saving money any way I can!!
Good posts from the others, Misky, but one thing still bugs me.
I'm assuming that, for the first winter, everything worked well?
You managed your temp. of 22 degrees?

If it was fine then, then something must have developed since to cause this problem.
What is the make and model of the boiler?
................ also ..............

how many radiators?
Question Author
Hi, some good tips to follow, but Builder - I can't check the make of the boiler as I'm at work. We got the burner because we were used to having a really warm house from the coke fire (too warm for most people who came round), and the radiators just didn't live up to it. We light the burner every night now, and have done since about October-ish. It's a different kind of warmth from a fire than from a radiator though and we miss it. And yes, the radiators were reaching the 22 degrees on their own till about Christmas-time. It's ready for a service but they won't come out during lockdown unless it's an emergency, otherwise we would have asked the engineer.
Question Author
Oops! Eight radiators, and sorry Joe, I answered your question in amongst my last answer, so it's jumbled up. We missed having a fire basically!
joeski we have central heating, but have a logburner in one room and a log effect calor gas stove in the other, purely for decorative effect, don't need them but like them.
It is absolutely correct to say that you must start with some assumptions when designing a central heating system and you choose what are the minimum results/capacity/capability in your chosen worst case scenario. But it is necessary to over-design for each room to some extent and then expect that possibly somewhere there will be excess output capacity rather than a deficit. Unless the rooms are all the same size and with the same thermal characteristics then the radiators will vary in size, which is why I can never understand why people such as inhibitor producers and others refer to the number of radiators in a house. In my house I suspect the largest radiator has of the order of 5-7 times the output capacity of the smallest which also compared to the rest is clearly the smallest.

My reaction to your description was the same as The Builder's, that something has changed but on the other hand it may simply be the effect of weather and your expectations being higher this time around. It is possible that your system managed to cope last year but that this year the demand has been higher (colder and/or greater losses) so that this time it is being stretched beyond its capacity.

Even in 2021 central heating is something of a mystery in the UK. Part of this is because housing in the UK has extremely poor thermal characteristics which are in some cases impossible to accurately evaluate (from windows, doors, etc. to absence of insulation, central cooling, etc.), part of it is lack of understanding of the basics (including by the "experts") and part due to the way the heating is used (primarily when it is deliberately rationed). The concept of having decorative heating components is a peculiarly British preoccupation, heating for heating's sake has still not really caught on and in general heating has a rather low priority with parts/whole of houses routinely receiving intermittent heating only and others none at all. Dampness/condensation is pretty widespread and regular occurrences of discomfort close to universal. Design criteria in the UK are routinely set at quite modest thresholds which so often end up disappointing.
KARL // why I can never understand why people such as inhibitor producers and others refer to the number of radiators in a house.//

I think the answer is fairly simple. What is the total volume of water in your system, boiler + pipes + radiators etc? I bet you don't know. How many radiators do you have? If you don't know you can count them easily and they give a rough idea of how big your system is, so how much inhibitor you'll need. It's not accurate but it doesn't have to be and calculating the volume of water in your system is rather complicated.

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