Radiator temp drop

[gaz1]

forget the book and forget the temp when leaving the rad its makes jack all difference

if you have balanced your system right by slowing down your return feed then the return boiler pipe temp is whats needed

across the rads means nothing due to there size as a smaller rad will return faster to a larger size rad that takes longer for the water to return via the return pipe

truth in the matter is it dosnt matter as those radiators start to heat up more and more from cold then the flowing temp will slowly start to hit the return temp on the boiler the longer the system is turned on

this is what happens when you have a woodstove or a coal burning back boiler as it dosnt shut down

 

[Gareth J]

What does the manual say? I know my boiler manual was pretty specific about efficient return temperatures but also keeping return temps above sensible minimum (once circulating) too.

That's an oil boiler though.

 

[RaceDiagnostics]

The user manual says nothing about return temps. I need to find a copy of the installation manual.

 

[JimmyS]

You can set the return temp if you want but it's only really appropriate if you have done heat losses and worked out rad sizes on a specific mean water temp. You may have some. Rads that are plenty big and others that struggle? You are as well turning the pump speed down as the lower the pressure the lower the flowrate will be and hopefully the higher the temp drop will be over the rads. Then take all the trvs off and do a rough temperature balance to achieve say a 20 deg drop over main rads towel rails will be a struggle so I'd try 10 over them. Once you have it roughly balanced you would see how room temps are. If you have a room that's a lot warmer than needed the rad is oversized and you can wind the lockshield in a bit and if a, rooms struggling to reach temp then open the lockshield. Once you have all the rooms about right you can stick the trv heads back on and they will trim the flows to suit what you have them set to temperature wise going forward. That's about as good a way as any IMHO.

 

[RaceDiagnostics]

So you are saying that I should expect to see 27Deg on the rad returns. I just can see that being possible.

 

[123hotchef]

i didnt balance mine with the lockshield valves when i re did the system I just left them fuly open, in the hope that the TRVs did the job. Right or wrong I dont know but it heats the house nicely

 

[JimmyS]

So you are saying that I should expect to see 27Deg on the rad returns. I just can see that being possible.

No, see if you can get 20 and take it from there. You really just want to roughly balance till you get rooms at about the right temp with no trvs on. 20 deg drop may not be possible if rads are on small side for room for example.

 

[JimmyS]

i didnt balance mine with the lockshield valves when i re did the system I just left them fuly open, in the hope that the TRVs did the job. Right or wrong I dont know but it heats the house nicely

Most of the time you don't need to bother temp balancing as trvs will close and force water to other rads that are maybe not getting enough. Sometimes it's handy on big houses if there's no commissioning valves and some rooms are cold etc.

 

[RaceDiagnostics]

i didnt balance mine with the lockshield valves when i re did the system I just left them fuly open, in the hope that the TRVs did the job. Right or wrong I dont know but it heats the house nicely

That's how mine were before I started messing with them with the hope to get it more efficient. However I don't know if achieving 50 send and 42 return at the boiler is in fact any worse than 50 send and 30 return.

I'm not really seeing anything specific on the web either.

My gut feeling is, as long as the return is below the dew point it probably makes naff all difference.

 

[JimmyS]

The lower below dew point the better but 42 return is pretty decent I'd say

 

[gaz1]

You can set the return temp if you want but it's only really appropriate if you have done heat losses and worked out rad sizes on a specific mean water temp. You may have some. Rads that are plenty big and others that struggle? You are as well turning the pump speed down as the lower the pressure the lower the flowrate will be and hopefully the higher the temp drop will be over the rads. Then take all the trvs off and do a rough temperature balance to achieve say a 20 deg drop over main rads towel rails will be a struggle so I'd try 10 over them. Once you have it roughly balanced you would see how room temps are. If you have a room that's a lot warmer than needed the rad is oversized and you can wind the lockshield in a bit and if a, rooms struggling to reach temp then open the lockshield. Once you have all the rooms about right you can stick the trv heads back on and they will trim the flows to suit what you have them set to temperature wise going forward. That's about as good a way as any IMHO.

sorry it dosnt work like that never has done

pump is used more in reference to a length of system to reach the furthest radiator you cant pump more flow into a rad and have more flow out the rad if its been balanced correctly so the longer the system the higher the pump speed to reach the furthest radiator in the house

upstairs downstairs rads work differently you need the upstairs return side more closed compared to the downstairs rad as heat always travels upwards leaving the downstairs feeling colder and sometimes not even heated on poorly piped systems

its also the same with length of pipes needed to travel so you need the furthest radiator to get a good amount of heat to it from the boiler the way to do this is open up the return side more so it travels quicker to it and higher the speed on the pump

oversize and underside rads makes no difference its all about the returning water temperature back to the boiler

trvs only come into the equastion after the return flow is set equal for all rads

if owners go out and buy a stupid towel rail rad and remove the bathroom rad theres no point in turning it higher as its really doing nothin other then unequaling there systems because the owner thinks its going to get more warmer in that room
or for stupid idiots who coment that it will make the room hotter by having more flow through it the only way that bathroom is going to get more warmer is fit another radiator at side of it

its also the same with a smaller radiator you cannot gain more heat by giving that smaller radiator more flow other than unequaling your return system

 

[JimmyS]

The pump is sized to suit the index run of the circuit not longest pipe run as pressure losses depend on pipe diameter and design flowrate not necessarily pipe lengths also flow control valves, types of heat exchangers valve authority and such like.

Upstairs and downstairs rads work the same hydraulically. Yes heat losses are affected but not sure what your point is.

Point 3 - index circuit would normally have minimal restrictions so in case of rads lsv would be left open when you say travels quicker it travels at the flowrate needed to meet design conditions

Oversized or undersized radiators impact return water temp at design if oversized then return water temp can be lower as mean water temp in rad can be lower.

You wouldn't set the flow equal to all radiators flow depends on rad output?

Heat output of a towel rail or any other rad will increase if flowrate is increased as mean water temp in emitter increases but it can only vary as a percentage of nominal output so possibly only 10% and 10% of not much output to begin with is the issue. Output of chrome plated rads is lower than painted as well due to emissivity of surface.

With regards last point, as noted above output does increase but return water temp increases

 

[Pigeon_Droppings2]

i didnt balance mine with the lockshield valves when i re did the system I just left them fuly open, in the hope that the TRVs did the job

The problems start when people turn the TRV to "max"...then leave the window open. In that case one radiator can short-circuit the system and the other rads just get a rubbish amount of hot water.

I think the ideal situation is that all rads always get some hot water flow and heat up evenly (up tot he TRV setting)...although I have yet to achieve this myself so maybe don't listen to me

I'm still running one rad half full of air....to compensate for the busted expansion vessel I was meant to change in the summer....and totally forgot!

 

[RaceDiagnostics]

Well I got them all balanced nicely, then the next morning found the upstairs radiators were only warm and not hot, till 8.30 when they got hot.

The hot water part of the heating turns off at 8.30 so the valve to the cylinder closes then. So now the hot water cylinder circuit totally screws up the balancing. Now wishing I hadn't touched it.

Should have thought about that, funny how none of the YouTube videos even discuss this as an issue, most are total bs, been giving plenty thumbs down.

 

[Mikey D]

I'm probably wrong but shouldn't the boiler just heat the radiators or the hot water cylinder not both at once ?

 

[RaceDiagnostics]

On my system the hot water tank is effectively just like another radiator in parallel with the others except it has a motorised valve controlled by the timer.

On my old gravity fed system the hot water was on whenever the heating was on, the new system is slightly more advanced than that.

 

[Dee J]

I'm probably wrong but shouldn't the boiler just heat the radiators or the hot water cylinder not both at once ?

Depends on how things are set up, but both S and Y plan can deliver heat to both simultaneously (and most basic timer/controllers do just that). Would you have it that that, after running a bath (for example), the boiler would be so focused on reheating the tank that the rads would go cold? Heating boilers and their controls have for decades been compromises of cost and simplicity of operation, and common timing for heat and water is really quite common.

 

[RaceDiagnostics]

I guess I can just change the hot water timing to do a heating cycle just before the central heating comes on so there is no conflict.

 

[gaz1]

Well I got them all balanced nicely, then the next morning found the upstairs radiators were only warm and not hot, till 8.30 when they got hot.

The hot water part of the heating turns off at 8.30 so the valve to the cylinder closes then. So now the hot water cylinder circuit totally screws up the balancing. Now wishing I hadn't touched it.

Should have thought about that, funny how none of the YouTube videos even discuss this as an issue, most are total bs, been giving plenty thumbs down.

just to make it clear thats correct however you also need to do the same with your hot water cylinder

so youve done this

and now you need to do this

 

[RaceDiagnostics]

I was about to say, there is no valve on the hot water circuit till I went for another look, the red tap is fully open so was short circuiting the radiators. I'll throttle that down a bit to be sure the boiler is in condensing mode but have also now set up the hot water timer so there is no overlap with the heating.