Tacanova is directly after the pump and bridges the 30 cm or so between flow and return.
Heating circulator incorrectly sized?
- Thread starter bhm1712
- Start date
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Not sure whether it matters or not but the control circuit had been wired such that you cannot have more than 2 out of the three circuits running at once so it's either HW and CH, HW and Dehum or CH and Dehum.
How did he work that out? And did he take into account the reduction in output due to lower working temperatures?
Is the house warm enough?
Have you ever worked out the heating requirement of your house? Baxi Whole House Boiler Size Calculator is quick and easy.
House is sweltering to be honest and I assume (rightly or wrongly at the moment without speaking to him) that he calculated based on rad sizes.
All he said regarding the temperature and output other than this was that to get the boiler into full efficiency the rads are too small to efficiently heat the house with a lower flow temp
All he said regarding the temperature and output other than this was that to get the boiler into full efficiency the rads are too small to efficiently heat the house with a lower flow temp
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It does take a little longer to heat up to be honest but the boiler is in a lower modulation after 10 minutes than it ever has been whilst I've lived there and when my mum lived there. You can barely hear the boiler now when before you could always hear the fan on a fairly high speed
I can actually hear water dripping down the condensate pipe.....
That implies that the rads are more than enough to heat the house.
It would be helpful to know what the Baxi calculator says (link in my last post). Set hot water requirement to 0.
As a rough guide (will need to measure to be precise with the width and length of the home etc) it says the requirement is 19.7kw
I have just read all these postings for the first time.
My initial reaction is that its pleasing that I have not wasted any time before on it.
Just shows how a professional can do so much in a short time.
BUT there is still one totally unexplained problem! How can a flow pipe ( said to be in 28 mm ) suddenly lose 8 C ( that's 70 C less 62 C ) on the way to the last two rads???
I would be investigating that as it seems to be a non compliance with the laws of physics! Not trying to overcome the problem with a larger pump.
I don't understand how this Tacanova valve is giving any benefit when a normal ABV would usually be used.
Tony
My initial reaction is that its pleasing that I have not wasted any time before on it.
Just shows how a professional can do so much in a short time.
BUT there is still one totally unexplained problem! How can a flow pipe ( said to be in 28 mm ) suddenly lose 8 C ( that's 70 C less 62 C ) on the way to the last two rads???
I would be investigating that as it seems to be a non compliance with the laws of physics! Not trying to overcome the problem with a larger pump.
I don't understand how this Tacanova valve is giving any benefit when a normal ABV would usually be used.
Tony
he was on it for 18 hours! Far longer than I spent on it! And he quoted for 4 hours and stuck by it as well! Said he wouldn't charge more because it became a challenge that he wanted to solve personally. Saturday and Sunday he came! That was very honourable of him. However he only adjusted the original 18 degree differential I set the drop across the radiators to 15 degrees and changed the flow temp to 70. He also discovered the dehumidifier circuit when he lifted the boards adjacent to the HW cylinder. so I can't understand why 2 of the original 4 colder radiators now have a warmer inlet temperature - unexplained by him and I can't think why either. Other than that not much extra has been achieved... Still plenty of anomalies which don't make sense as you have pointed out.
Assuming that excludes any allowance for hot water, the rads are slightly undersized.
22.8kW with a flow of 70C and return of 55C will actually produce 17.6kW of heat, which is 2kW less than you need. 75C/55C would give 18.9kW. Bearing in mind that this is only required on the few days a year when the temperature is below freezing, it may not be worth doing anything about.
Like Tony, I can't fathom out how 8C can be lost along a short length of pipe. Is it exposed to cold draughts? If so, insulating the pipes would help.
Is the house well insulated? Doing that would be better than larger rads.
As for the pump, 17.6kW at 15C gives a flow rate of 1.0m³/hr. Taking the 1.5m boiler loss into account and the 2x30m longest run, the Grundfos calculator says you have a 3.9m head. Looking at the UPS 15-60 graph, this will be achieved when set to speed 2. Has your installer looked at the UPS2 25-80 graph and does he realize it is 180mm between connections, not 130mm?
Is the Tacanova Setter on 15mm, 22mm or 28mm pipe?
The tacanova setter is in 22mm
He has now advised replacing the taconova with an ABV as after reading the boiler manual he says it specifies an automatic bypass not a fixed bypass. Do you agree with that?
You said the Setter is set to 2, which is 2 litres/min. 1m³/hr is 16.67 litres/min; so 12% of the heat is being sent straight back to the boiler. This not only reduces the heat available to the rads but, more importantly, raises the return temperature unnecessarily.
As an experiment, set all TRVs to max and reduce the Setter flow to zero (make a note of which letter it is on). Then see what effect it has on the two problem rads. Reset TRVs and setter.
Last edited:
Didn't see this until I had posted my last comment.
Short answer: Yes.
A fixed bypass is no longer allowed by Building Regulations.
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