Heating system

[Yellow Bear]

An option that is not cheap but may save you both time and money is to replace the thermostatic heads with the electronic versions now available which allow the setting of different temperatures at different times of day dependent on usage.  This may work out cheaper than zoning as it is non intrusive.

eg  Bedrooms   -  20 first thing reducing to say 17 through the day and back to 20 at say 2100 then say 15 overnight.

       lounge        -    17 through day when not in use rising to 21 at say 1700 and may-hap 13 overnight

This means you are only fully heating rooms you will be using at the respective time of day.    This will effectively  "fine balance" the system.  as you rarely require all rooms at "maximum" temperature at the same time or the same temperature any one room at all times dependent on activities.

Also, assuming  the pipework is only 15/22mm throughout using a standard domestic pump with 21 rad it will need to be on the highest setting.

 

[JohnfromUK]

36 minutes ago, Yellow Bear said:

An option that is not cheap but may save you both time and money is to replace the thermostatic heads with the electronic versions

I looked into this (a Honeywell Evohome system) for my system.  It was VERY expensive (about £50 extra per radiator) and I doubted it would ever be cost effective.  It also needs the batteries changed in every TRV device annually, and so that was extra work and cost.  I also question whether I would ever make use of that level of complexity.

To install a hard wired system to 30 radiators was prohibitive on cost grounds.

It's a nice idea, but not likely to recover costs ever.  I was also concerned (without any hard evidence) about the reliability, being as it is radio/WiFi dependant.

Because I was fully re-plumbing (part of a major rebuilding), zoning (4 zones) by normal electric valve, time clock and thermostat operation valves was not a great additional expense and provides a reasonable compromise between control flexibility and simplicity.

[Yellow Bear]

3 minutes ago, JohnfromUK said:

I looked into this (a Honeywell Evohome system) for my system.  It was VERY expensive (about £50 extra per radiator) and I doubted it would ever be cost effective.  It also needs the batteries changed in every TRV device annually, and so that was extra work and cost.  I also question whether I would ever make use of that level of complexity.

To install a hard wired system to 30 radiators was prohibitive on cost grounds.

It's a nice idea, but not likely to recover costs ever.  I was also concerned (without any hard evidence) about the reliability, being as it is radio/WiFi dependant.

Because I was fully re-plumbing (part of a major rebuilding), zoning (4 zones) by normal electric valve, time clock and thermostat operation valves was not a great additional expense and provides a reasonable compromise between control flexibility and simplicity.

There are any number out there at the moment -  if you buy Honeywell they hit you for the name for a start.   yes you need to change batteries about every 2 years.

I have seen reasonable ones for about £25 if you buy in Bulk (10+) so for 20 rads that is £500  =  if you need to employ a plumber?heating eng to fit even 2 zone valves it will cost that and you have the disruption.

[JohnfromUK]

1 minute ago, Yellow Bear said:

There are any number out there at the moment -  if you buy Honeywell they hit you for the name for a start.   yes you need to change batteries about every 2 years.

I have seen reasonable ones for about £25 if you buy in Bulk (10+) so for 20 rads that is £500  =  if you need to employ a plumber?heating eng to fit even 2 zone valves it will cost that and you have the disruption.

There is no doubt such systems have a place.  However, it wasn't for me. 

I have had a zoned system for over 30 years now, and have found zoning +TRVs gives a good mix of control with low maintenance and very good long term reliability.  The 'old system' was installed in 1986 re-using earlier pipework and radiators and with a very early condensing boiler and replaced in 2016, still working fine after 30 years.  In that time I had one electric valve failure, one thermostat failure - and numerous TRVs sticking, easily cured, but an annual occurrence on the early TRVs.

The 2016 complete replacement was and part of a major rebuilding project and mainly due to risks of corrosion in 30 (and more in many cases) year old radiators and pipes.

[Yellow Bear]

Fair enough, however the OP was in the position requiring retro fit and to be honest even with zone valves I would still use time span thermostats.

[JohnfromUK]

The main purpose of my original post was to assist in balancing a larger system, which can take some doing.  I do agree that the electronic timed TRVs represent an easy install as a retrofit, whereas zoning is often near impossible as retrofit.

[Cosd]

7 hours ago, Tim Kelly said:

If you have 21 rads, you definitely need to balance the system well. You might well need a bigger pump too, something like a 25-50 as the resistance of the system might be too much for a standard pump. Has the heating system ever worked well?

 

If you don't have them, TRVs (thermostatic radiator valves) if used correctly will help balance your house heating as the upstairs rooms which heat up well will shut down the radiator once the room is warm enough, which sends more heating potential to the cooler parts of the house.

The system did work well when we bought it but room downstairs were smaller. We joined three of the rooms into one large kitchen diner and floor to ceiling sliding doors. Doing this we reconfigured the rads making them bigger for higher BTU. 

 

Do have Drayton TRV4’s on all the new rads. All the old rads also have older style TRV’s, they look like Honeywell. All these will be changed in time also.  

6 hours ago, JohnfromUK said:

I have about 30 rads in a 4 zone system, completely renewed (all rads, all pipework, boiler, 42KW Worcester Bosch condensing gas boiler, all hot water system) 2 years ago. It is in a rambling old house and some of the pipe runs are long and complex, with lots of bends getting round beams and walls.   I have a few comments based on experience.

1. Room calculations are a reasonable guide, but some rooms are naturally cold, some naturally warm.  Wind exposure, windows, drafts, insulation, doors left open all make a difference.  I have 50% extra radiator capacity in some places that I know to be 'cold' and it is still a bit marginal in cold windy weather.  Big rooms in particular seem to need more than calculations show unless you are prepared for  very slow warm up time.
2. Rads work by convection, so the top will always be hottest, and the water falls down the rad as it gives up its heat.  Generally modern condensing boilers have a 20ºC difference between flow and return (older boilers were less, 11ºC in some models if I remember right).  In modern systems, a 'two pipe' system is used where all of the radiators have a 'flow' sourced from the boiler, and a 'return' going back to the boiler.  Therefore, on average each rad inlet should be at boiler 'flow' temperature, which will be around 65-70ºC , and return about 50ºC which allows the boiler to condense correctly.  Flow water goes straight to the top of the radiator and the water sinks down the radiator, giving up its heat before flowing out, roughly 20ºC  cooler.  The top will therefore be about 15 - 20ºC  warmer than the bottom.
3. If a rad is dropping more temperature than this, the flow through it is too slow.  If there is little temperature change between flow and return, the flow is too fast.
4. Balancing the rads in a big system is hard to get right, (more so in a multi zoned system), but generally, each rad should drop about 15 - 20ºC between flow and return.  Note that TRVs should be open when balancing, or you may end up chasing your tail, because as you try and increase flow on the lockshield, the TRV may be reducing it at the other end!
5. Small rads therefore need less water flow than big rads.
6. Rads close to the boiler will tend to naturally get a higher pressure/flow as pipework looses pressure with distance (and bends, thin pipes etc.)
7. The method I have found works best in practice (starting from scratch) goes a bit like this;
8. Fully open the lockshields and TRV/Flow valves on all radiators.
9. Close down the lockshields on smaller rads (and those closest to the boiler) which get hot very quickly and have no apparent temperature drop between flow and return. I use a cheap eBay infra red thermometer (about £10) to get about 15 to 20ºC  drop across rads.  An investment you should recoup in savings when all is set up right.
10. Big rads you will probably leave the lockshields fully open, and only balance down those that clearly have a very fast flow.

It is quite hard to get right in a big system, and you have to be patient.

Thanks for the in depth reply.  Some useful information!!

[Cosd]

4 hours ago, Flyboy1950 said:

I think that JohnfromUK has given you sound advice. I have reread your original post and quote "Rads are good quality and I went over the recommended BTU per room." New rads are likely to have less resistance to water flow and hot water takes the least line of resistance, also as they are bigger you are compounding your problem further. You must also now consider whether your boiler is man enough for the extra requirement placed on it in its present and future forms as you replace even more radiators. Possibly having reached the point of the straw breaking the camels back.

Maybe depending on your home layout and requirements you could divide your house into 2 zones with the upstairs running at a cooler temperature and times? Cheaper than a bigger boiler that you wont need in the summer, so more fuel efficient.

Every time you replace a radiator you will upset the balance of the system.

The boiler is a Worcester FS30CDI which is 32.1kw. 

I have no idea if that is powerful enough. 

[Cosd]

7 hours ago, Tim Kelly said:

If you have 21 rads, you definitely need to balance the system well. You might well need a bigger pump too, something like a 25-50 as the resistance of the system might be too much for a standard pump. Has the heating system ever worked well?

 

If you don't have them, TRVs (thermostatic radiator valves) if used correctly will help balance your house heating as the upstairs rooms which heat up well will shut down the radiator once the room is warm enough, which sends more heating potential to the cooler parts of the house.

This is what is on the system. 

Again, I have no idea of this is a “Standard” pump or powerful enough. 

[Cosd]

3 hours ago, Yellow Bear said:

An option that is not cheap but may save you both time and money is to replace the thermostatic heads with the electronic versions now available which allow the setting of different temperatures at different times of day dependent on usage.  This may work out cheaper than zoning as it is non intrusive.

eg  Bedrooms   -  20 first thing reducing to say 17 through the day and back to 20 at say 2100 then say 15 overnight.

       lounge        -    17 through day when not in use rising to 21 at say 1700 and may-hap 13 overnight

This means you are only fully heating rooms you will be using at the respective time of day.    This will effectively  "fine balance" the system.  as you rarely require all rooms at "maximum" temperature at the same time or the same temperature any one room at all times dependent on activities.

Also, assuming  the pipework is only 15/22mm throughout using a standard domestic pump with 21 rad it will need to be on the highest setting.

 

I did look at these but if I’m honest, I didn’t like the look of them being a little bulky, but also not sure I need so much control. 

I’ve also got a couple of mates that have spent a small fortune on this stuff and they’ve had problems which just puts me off, I think TRVs are probably ample for me. 

[Yellow Bear]

13 minutes ago, Cosd said:

This is what is on the system. 

Again, I have no idea of this is a “Standard” pump or powerful enough. 

the speed control on the top should be set to  III

[Cosd]

6 minutes ago, Yellow Bear said:

the speed control on the top should be set to  III

It was set to III

Would you say this is powerful enough?

Edited March 4, 2018 by Cosd

[vampire]

I am not a gas engineer only do oil,but is 32kw gas boiler ok for 21 rads,whats total btu for those rads,do you have/need extra expansion vessel would be my guess.

Yes, you do add inhibitor via sludge filter,after you have taken mag out and cleaned it,but you would be far better to add a cleanser then flush that out before adding inhibitor and two or three bottles ?

 

[figgy]

With 21 radiators i would be fitting a secondary circulating pump, Your asking a lot of the current pump.

[JohnfromUK]

10 hours ago, Cosd said:

The boiler is a Worcester FS30CDI which is 32.1kw. 

I have no idea if that is powerful enough. 

Mine is a Worcester FS42 CDI.  I have counted up, and it does 28 radiators, of which 23 are double convectors (average to large mostly), and hot water in a mains pressure cylinder (set up as a fifth zone).  I have a similar single pump, and in fact works fine set on I (out of III).  In very simple terms 32 kw for 21 rads is similar per rad.

My system has the boiler dial set to No. 5 in normal weather giving flow about 65ºC and return (once warmed through) about 45ºC.

One 'trick' I do practice is to heat the hot water (separate timed and thermostat controlled zone) before the heating comes on in the morning, because the water heating does upset the 'balance' by being a very easy flow route.  Water is heated 05:30 to 06:30 when the heating starts.  The water is hot by then and gives me plenty all day.

Your problem of some radiators hot all through, and some hot at the top only is classic of unbalanced flow in my view.

I have found the Worcester FS xx CDI very good so far (just over 2 years now).

Without knowing all the details, your 32.1kw sound the right ballpark.

[Tim Kelly]

If the pipework is well designed then the resistance is low, so a normal pump is fine. If the system has been extended by builders and poorly designed in the first place, there could be a lot of resistance, so a bigger pump might be needed. A good go at balancing the radiators properly will tell you whether it is possible or whether you need to boost the circulation.

[figgy]

A good flow of water through a system keeps sludge build up in the rads to a minimum.

[JohnfromUK]

1 minute ago, figgy said:

A good flow of water through a system keeps sludge build up in the rads to a minimum.

That is true, though my old system which ran for 30 years and no filter (though it had inhibitor added regularly) had no sludge problems and even when we took it all out, there was very little sludge anywhere.   Some radiators were 50 years old when scrapped (I reused from the original system put in in 1966) and no leaks or pinholes.  A tribute to the use of inhibitors.

[Cosd]

5 hours ago, Tim Kelly said:

If the pipework is well designed then the resistance is low, so a normal pump is fine. If the system has been extended by builders and poorly designed in the first place, there could be a lot of resistance, so a bigger pump might be needed. A good go at balancing the radiators properly will tell you whether it is possible or whether you need to boost the circulation.

The house as said is some 30 years old and all original without any extensions added, I can tell the boiler was replaced but the rads were all original.

The changes have just been made now where we knocked 3 rooms into one, and I got my plumbers to do this so confident the pipework is good. I'm keen to get it sorted because we are going to be creating another lounge so another 2 rads will be added to the system.

 

Reading this and the other posts, it does seem to be a balancing problem, so I will look at doing that first; I'll invest in one of those laser thermometer gizmo's to do a much more accurate balance this time round. 

 

[JohnfromUK]

I think this is probably your solution;  They key is to get the temperature drop across the radiators to about 20ºC on each radiator.  This is what your boiler 'expects' to see.  If the flow is about 65ºC, then the return will be approx 45ºC, which will enable the boiler to operate correctly in condensing mode.  This should happen with the control on your Worcester boiler set to about No 5.  When it is very cold you can turn it up more, but it will use more gas as with the return above 55ºC you will not get much condensing effect.

Note that IF you boiler also heats hot water via a cylinder with an inner coil, you will need a flow of about 65ºC minimum to ensure that the water gets to a safe temperature - permanently too cold can lead to a legionella risk, though it seems very uncommon (if it happens at all) in domestic installations.  Also check that IF there is a thermostat on the water tank operating a valve, that this is working and shutting the valve when water is up to temperature.  As mentioned in an earlier post, I arrange to heat the water at a different time, because the water cylinder coil does upset the balance by providing an 'easy route'.

It is quite time consuming and tedious to get right because each time you make change, it takes time for the temperature on each rad to stablise.  Start with the lockshields on the biggest/furthest fully open.

The infra red thermometers are cheap and also quite good at showing up and cols spots on walls/ceilings etc.

[old man]

Not read all of this but first thought 30 year old pipework. How are rads plumbed.? Series or parallel?

[sandspider]

Had a power flush on my CH system when we had a new boiler installed. Cost about £250 IIRC. Having said that, it didn't get all the sludge out of the two worst radiators (annoyingly). I had to get the plumber back, and we took the worst rads off the wall, took them out into the garden and put a hose through them. We also had one fall over, and that got a lot more black stuff out of it! So in my experience, power flushing doesn't do that much to serious sludge buildup...

[Cosd]

8 hours ago, JohnfromUK said:

I think this is probably your solution;  They key is to get the temperature drop across the radiators to about 20ºC on each radiator.  This is what your boiler 'expects' to see.  If the flow is about 65ºC, then the return will be approx 45ºC, which will enable the boiler to operate correctly in condensing mode.  This should happen with the control on your Worcester boiler set to about No 5.  When it is very cold you can turn it up more, but it will use more gas as with the return above 55ºC you will not get much condensing effect.

Note that IF you boiler also heats hot water via a cylinder with an inner coil, you will need a flow of about 65ºC minimum to ensure that the water gets to a safe temperature - permanently too cold can lead to a legionella risk, though it seems very uncommon (if it happens at all) in domestic installations.  Also check that IF there is a thermostat on the water tank operating a valve, that this is working and shutting the valve when water is up to temperature.  As mentioned in an earlier post, I arrange to heat the water at a different time, because the water cylinder coil does upset the balance by providing an 'easy route'.

It is quite time consuming and tedious to get right because each time you make change, it takes time for the temperature on each rad to stablise.  Start with the lockshields on the biggest/furthest fully open.

The infra red thermometers are cheap and also quite good at showing up and cols spots on walls/ceilings etc.

I have to admit at being a little lost around M.D. the hot water part. I have a Megaflo pressurised system. 

 

Apologies if if this sounds silly, but are both temps taken on the rad next to each valve, in and out?

7 hours ago, old man said:

Not read all of this but first thought 30 year old pipework. How are rads plumbed.? Series or parallel?

I have no idea I’m afraid

[shootthepigeon]

The way I remember it from way back when at college, the difference between flow and return should be 11°C at the valves, to give optimum performance, there should be at least 22°C between the f+r at the boiler to optimise the boilers efficiency.

[old man]

Have seen old system where radiators connected in series so water gets colder the more rads it passes through.