Central heating pump sizing

[king of pipes]

Pm him I am sure he will have a explanation

You will get particles that will build up in the burner chamber that won’t get flushed through with the condense and will build up to a point where it just blocks the hex and could cause it to split

Like this

 

[ShaunCorbs]

Pm him I am sure he will have a explanation

Like this

forgot to reply yesterday

 

[Reddwarf4ever]

That does make sense, but wonder how many condensing boilers are actually running in condensing mode ? Maybe apart from new installs mine not been condensing since new in 2009, only since January 2021 have I been trying, but still not a great success, minimum return temperature 53-55oC, only thing I can do is replace two lounge radiators with double fin, each would then give approx 30% extra heat output ( 100cm x 50 cm )

 

[king of pipes]

I am sure it will be condensing at certain times of the day, I by no means have John G' s grasp of the figures but I have 80 + boilers on my books which I service and maintain, and where possible I advise my customers to keep the flow temperature setting at 65° c by keeping the heat exchanger clean serviced correctly and that means a full strip and clean every year flushed though electrodes cleaned condense trap removed and fully cleaned or replaced any small leaks addressed gas valve adjusted , every 5 years the system drained flushed and a good quality inhibitor added I rarely get a breakdown from doing a flue gas analysis which we do on each service you can determine efficiency at different stages of firing , modulation, and flue gas temperature I personally think you have probably got your system running the best you can without changing things replace radiators for larger ones by all means this allows you to run the system at a lower temperature and still be comfortable in your living space. Regards kop

 

[John.g]

The boiler will certainly condense very heavily on start up in the morning where it might take a 18kw boiler ~ 10 minutes to heat say 75 litres of water from 20c to 50C, also if the house/room temp is very cold then a certain amount of condensing will also take place.

Its interesting though that if you have a fixed flow temp of 65C and a flow of 0.75m3/hr (fairly normal for a 18/20 boiler) then no matter how oversized the rads are that the return temp cannot be lower than ~ 51C once the rooms are up to temperature (I use 23C) the room temp and the return temp will then start rising.
I spoke to a (long retired) acquaintance of mine earlier on and he said he never remembers measuring a gas fired boiler flue gas temp below 55C, what kind of flue gas temps are you seeing KOP?.

 

[king of pipes]

I am working on one now as we speak

 

[John.g]

Boiler NO 81? should now be be running at 65C/0.39M3/hr (flow) and rad(s) output of 59% OR
55C/0.77M3/hr (flow) and rad(s) output of 48%.
and Shaun's condensate flow at roughly 0.7 lit/hr @ 20 kw boiler output or pro rata.

 

[king of pipes]

I am working on one now as we speak

Bit cleaner now

 

[John.g]

That's some service.

 

[Reddwarf4ever]

I thought the same thing as John mentioned, when the boiler first fires up in the morning, return temperature is typically 20-25oC & after it cuts out on the room stat, may not restart for 1-2 hours, then again very low return temperature for some time ( will try and monitor return temperature next time it restarts, be interesting to see the climb rate and how long it ‘ should be’ condensing for. So going back to deposits on the heat exchanger wouldn't these periods of heavy condensing keep the exchanger clean ? I am running my boiler outlet at 64oC, i tried 62oC, but even 2oC seemed to make noticeable difference to radiator heat output. The return temperature when steady and modulating is 53-56oC. As I said previously I was considering replacing 2 lounge radiators with double fin, but looks like the best I might get is a 45oC return temperature.....only an educated guess.....which would give a 3% saving, would take around 20-25 years to pay back the cost..so very likely going to abandon that idea.

I know I may get shouted at, but I dont suppose I could clean the heat exchanger myself, I think it will need a Gas Safe person most likely.......

there is a move to make manufacturers add an efficiency display to their boilers and show when it’s in condensing mode, I think they will fight hard against this, as people will soon realise they are not getting the 97% efficiency that they expect..

take care all & keep safe