Increasing radiator output and improving CH performance

[Mathew Newton]

I would appreciate some advice regarding my thinking-out-loud assessment of our heating system, and the best way to improve it somewhat if at all possible.

I've recently bought a relatively new (2007) 3-bed 2.5 storey semi which is obviously very well insulated and given the variety of sizes of radiator appears to have had the heating system designed through calculation, even if just following rules of thumb. The radiators, with output figures obtained from similar-looking Flomasta spec sheets, are:

(Room HxW Type Output) Kitchen 500x700 Double 1048W Hall 500x600 Double 898W Downstairs Loo 300x400 Single ~250W? (a real tiny one - I think it looks great!) Lounge 600x1000 Single 948W Conservatory 600x600 Double 1041W Front Bedroom 500x1000 Single 812W Rear Bedroom 500x1000 Single 812W Guest Bathroom 600x500 Double 868W Top Bedroom 400x700 Double ~1000W? En Suite 600x500 Single 488W Dressing Room 600x600 Single 570W

Total: 8735W

The boiler is a condensing Ideal Icos HE15 (I know - it's probably not the best place to start but it's what we've inherited and it seems to work well enough so I'm not looking to replace it just yet) which can modulate between 8.8kW and 14.6kW. It's an S-plan layout run in 10mm (the branches at least - I note the presence of 22mm at the boiler end and within the airing cupboard), with a digital CH stat in the lounge and a sealed indirect cylinder for the HW. The neighbours are only present at the weekend so for all intents and purposes I think their house is unheated most of the time.

I have a few issues that I'd like to address:

1. Whilst I have yet to perform a full and proper observation the boiler appears to cycle a fair bit even before the house is up to temperature. I am wondering if this is because the total radiator output (even before any necessary derating) is at/below that which the boiler can modulate down to? That is, the system cannot get rid of the heat quick enough so the boiler has no option but to cut out? As described below I am planning on increasing the size of some of the radiators - would this help?

1. The full-width conservatory was built after the house, and I am pretty sure that the 600x600 Double 1041W radiator in there was originally in the lounge under the window of the then outside wall i.e. they simply moved it from the inside to the 'outside'. It appears that this radiator is inadequate for heating the conservatory in colder weathers and whilst it has not been too much of a problem yet I think it may well be in the winter. For better or for worse we want to use the conservatory all year round so should I replace this radiator with something bigger? Or should I just supplement it with electric heating, perhaps a portable convector heater, as required? The latter might be beneficial for those times when we need a little heating in there when the CH is off (e.g. cooler summer nights).

2. Given the suspected re-siting of one of the lounge radiators into the conservatory this has left just the 600x1000 Single 948W in the lounge and it seems to struggle by itself to bring the temperature up in any reasonable time i.e. the rest of the house seems to reach target temperature (as set by their TRVs) well before the lounge yet I can confirm the lounge radiator is very hot to the touch so it does seems to be trying. I was thinking of replacing it with a 600x1400 Double 2428W (maybe bigger?) thus bringing the heat output in there back up to 2kW+ as originally designed. Does this sound sensible? Would it help with the cycling? The stat is in the lounge hence no TRV. The lounge opens into the conservatory, and for various reasons we may well want to keep the doors to it continuously open (or at least partly), and so it is obvious it will also be partially attempting to heat the conservatory too. I could add an additional radiator back in there (perhaps where the original second one was) but that'd be a bit more work - replacing the single radiator would be much easier.

Any thoughts? Sorry for the waffle, but hopefully it describes the situation for you to be able offer some advice.

Mathew

[fred]

In article , Mathew Newton writes

Step 1, balance the system. It may not have been done at all and the boiler cycling a lot even when warming up suggests inefficient transfer of heat to the rads.

[Mathew Newton]

Thanks Fred. I did think about that option but figured, perhaps erroneously, that as all the radiators were nice and hot then it probably wasn't an issue.

Could it be that if, say, some/all the LSVs were too open then water would be returning to the boiler too quickly hence would not have had sufficient heat extracted from it?

I think I may invest in an IR thermometer...

Mathew

[dom]

Have you checked whether the pump can go up a notch on speed?

My rather unscientific experience, based on having designed and installed just one oil-fired system, is that oversizing the radiators and running them at a lower temperature is good. Provides a gentler, more even heat to the rooms, to the point where I don't notice any temperature cycling. So yes, I wouldn't be concerned about moderately oversizing some of the rads. IR thermometer good too - even if to only confirm the current system is doing the best it can.

Heating a conservatory though - sounds like a way to tear up money in winter.

[Mathew Newton]

It is indeed on full whack. (For what it's worth it's an external Grundfos pump; one of the models suggested in the boiler installation instructions)

That'd be my ideal goal. Don't get me wrong, I'm not overly concerned with the current performance but if I can get the most of out it whilst we're in 'DIY mode' I'd like to particularly if can be done via minor adjustments rather than a fundamental redesign.

Yes, quite. My Dad suggested I might as well go the whole hog and put a radiator in the garden! ;-)

On that front we've decided to see how things go this winter with regards to energy consumption/costs and then make our minds up in the spring as to feasibility of using the conservatory all year round.

Mathew

[js.b1]

No, no, underfloor heating for the patio & driveway.

Just in case this winter is like 2009... you can at least get onto the iced up road :-)

[AlanD]

I think it depends largely on the efficiency of the conservatory. I added a fairly small conservatory last year (10 m2) with wet UFH embedded in the concrete floor slab, over 100mm foam insulation. The glass used in the roof is the IR reflective type stuff (slight blue tint to it), windows + doors typical double-glazed units. I expected to see a hike in my gas bills after heating it through the winter, however the increase is minimal - my monthly DD to the gas supplier has remained the same, even after their 'yearly review'. I guess the DD payments were slightly over my use before, and the conservatory heating has filled the gap, but it's really not much.

Mine is on it's own CH zone with it's own intelligent programmable 'stat. Because of the slow response nature of UFH it's set to come on earlier than the other zones and switch off (much) earlier too.

Alan.

[fred]

Still best to balance, I've just done a friend's system where they were ready to get a bigger boiler and put in more rads. Absolutely not necessary, after a balance the cold rooms are now toasty and the boiler could be turned down to save gas.

It's very common for certain installers to leave all the lockshields fully open so all the flow goes through the closest rads[1]. That would certainly result in cycling as the return temperature rises prematurely. This slows warmup time and may result in distant rads not reaching full temp.

[1] If pulled up on this laziness they will say that balancing is not necessary as the TRVs balance the system as the rooms warm up. This is complete bollocks of course for the reasons you are experiencing. Balancing allows the system to come up to temp quickly and evenly.

If you want to have a play then you can get a basic balance by hand. With a moderate boiler stat setting and the system up to temp the flow side should be uncomfortably hot to touch with the return side cooler but still the hot side of warm IYSWIM. Follow the FAQ for method.

Btw, TRV's should be fully open (set to max) for balancing.

[Mathew Newton]

Okay. Balancing it is. I will plump for an IR thermometer as I might as well take advantage of the excuse to get a new toy! ;-)

I've read the balancing FAQ and am clear about the process, however I do have a couple of (okay, 4) questions if I may:

1. Balancing order. The FAQ doesn't give much advice regarding what order to balance the rads in, whereas some other guides I've read talk about working out which is the furthest from the boiler (last to heat up) and working towards it i.e. leave it until last ideally with a fully-open LSV. Or is the FAQ also saying that by saying to leave the coolest rad fully open?
2. Target temperature drop. I know the Principles section of the FAQ says it really doesn't matter *what* the drop us, just that it's the

*same* everywhere. I'm struggling with this one. Is there really no target? Does the fact I'm using a condensing boiler, and have 10mm pipework bear any relevence on the issue? Surely if I balance the system such that the drop is 2C then that's not going to be any good? Is it? Or would I never reach such a situation?

1. Bypass. Does the radiator with no TRV (in the lounge, with the stat) need any special attention? E.g. should it's LSV remain fully open or anything. I ask given that this rad acts as my bypass if that matters.
2. HW. My HW circuit doesn't appear to have any LSV - is this an issue or does it not need any consideration? I imagine that if both HW and CH call for heat then the HW will certainly get first dibs given it's next to the pump and is run in 22mm so presumably quite low resistance. I'm more than happy for this to be the case.

Apologies if these are dumb questions... I'll admit to struggling a little understanding the issue 100% but would like to for my own benefit and ensuring I do a proper job.

Mathew

[Roger Mills]

Don't worry about location - start by turning down the lockshields on the rad(s) with the lowest temperature drops in order to reduce the drops on the others until they are all roughly the same.

For a non-condensing boiler, the target always used to be 11 degC (20 degF). I've no experience with condensing boilers, but have a feeling the the drop needs to be higher.

With an S-Plan system, you ain't got a by-pass unless you have a separate by-pass valve, 'cos when both zone valves shut there's nowhere for the water to go. Balance the non-TRV rad just like the others - except you may want to throttle that one a bit more to ensure that the rest of the house is up to TRV operating point before the room stat turns the whole lot off.

If you've got a fast recovery cylinder, it doesn't really matter. If you've got independent timing of CH and HW, you can contrive for them not usually to be on at the same time.

HTH!

[Mathew Newton]

Understood. Bad terminology on my part. Does the radiator with no TRV have another name, or is it simply an aspect of proper design?

It does, yes - thank you.

IR thermometer ordered so as soon as that arrives I'm good to go. Embarrassingly, I'm excited about the task actually although a part of me just knows that it could well turn into a hair-pulling exercise where cause and effect seem to have very little predictable correlation!

Mathew

[Roger Mills]

Assuming that there's a room stat which switches everything off when satisfied, it is usual for the room in which the room stat is located not to have a TRV on its radiator - otherwise you have two things trying to control the same commodity, and they will fight.

It's by no means an exact science, and you may end up with one or two rads with too low a drop even when throttled right back. That doesn't really matter as long as you don't have any with an excessively high drop relative to the target.

It pays to prepare a results sheet before you start, with a list of radiators in the first column and then several columns in which to record the flow and return temp of each rad for each iteration plus a record of what, if anything, you did to its lockshield after each pass. You'll need a few goes round the system at (say) 10 minute intervals to allow any valve position changes to take effect - but the beauty of using an IR thermometer is that you can rattle round the whole system very quickly.

When you've got the drops all more or less the same, you can move them all up or down if necessary by varying the pump speed.

I think someone has already said that you need to ensure that the TRVs are fully open during this exercise. I always remove the thermostatic heads from mine to make sure.

[fred]

Sounds like you're having fun (as was intended :-).

Not sure if the faq covers this but metal pipework and painted rads aren't that good at showing a correct temp on an IR thermometer (google emissivity). The solution is to wrap a turn of pvc insulating tape around your measuring points and target them with the IR and that will give a correct reading.

With my IR thermometer the precise alignment of measurement point vs the body isn't obvious so I have marked up the body with arrows that show the centre of the measurement field (the centre of the hole) to make alignment easier.

On the bypass issue, modern systems are best served by an automatic bypass valve (google) but maybe take one step at a time.

[Doctor Drivel]

Fit a Myson fan heater in the conservatory. This can have the fan running in summer to cool as well. They really do work well in conservatories and give heat instantly - no long warm ups. They take up little space. They operate when heat is in the pipes. If no heat the fan is off. Unless on summer mode.

The boiler is poor and only modulates down to 8kW. The better boilers go down to 3 to 5kW. Get a decent stat/programmer with boiler anti-cycle control

Balance the system up.

[Mathew Newton]

in summer to cool as well. =A0They really do work well in conservatories a= nd give heat instantly - no long warm ups.

I did consider that route but from the brief research I did the spec sheets seemed to suggest that 10mm pipework was inadequate - 15mm was the minimum. Presumably this is to deliver sufficient heat to make it effective? Running new pipework to the conservatory is unfortunately not really a viable option for me.

Yes. What I thought I might do is keep putting a bit aside each month for the when the bugger inevitable falls over and replace it.

I'm using a Honeywell CM907 but I'm not sure it's got anti-cycle control. Indeed if anything it's TPI control seems to give the boiler something a workout if I don't throttle down the maximum number of cycles per hour (ah.. I guess that might be the anti-cycle capability your refer to?).

Yup - will do.

Mathew

[Mathew Newton]

I'm googled out that front but still not sure what benefits it would give me. Surely my lounge rad always need to be kept fully open (whilst remaining balanced at least) in order that it is always able to output heat as part of the control loop with the room stat? If that is the case then are there any scenerios where an automatic bypass would be required to open? For what it's worth my particular boiler doesn't require pump overrun.

Mathew

[Doctor Drivel]

If fitting a Myson conservatory heater the heater can act as the by-pass. I fitted one and it was at the far end of the run. Worked well. The CH pipes were always hot and when the TRVs opened instant hot water at the TRV.

[Doctor Drivel]

I did consider that route but from the brief research I did the spec sheets seemed to suggest that 10mm pipework was inadequate - 15mm was the minimum. Presumably this is to deliver sufficient heat to make it effective? Running new pipework to the conservatory is unfortunately not really a viable option for me.

Yes. What I thought I might do is keep putting a bit aside each month for the when the bugger inevitable falls over and replace it.

I'm using a Honeywell CM907 but I'm not sure it's got anti-cycle control. Indeed if anything it's TPI control seems to give the boiler something a workout if I don't throttle down the maximum number of cycles per hour (ah.. I guess that might be the anti-cycle capability your refer to?).

Yup - will do.

Mathew

[Mathew Newton]

It just doesn't seem viable at this point in time as routing 15mm back to the manifolds (whereever they might be) would involve a fair amount intrusion to walls, ceilings and floors all of which are in no need of redecoration at the moment.

I'm not sure I like the aesthetics of them either if truth be told!

Mathew

[Roger Mills]

One of the main reasons for having a by-pass valve is to provide a flow path during pump over-run periods with all zone valves closed - but if your boiler doesn't require pump over-run, you don't need it for that purpose.

Another possible reason is to reduce pipe noise when all the TRVs are closed and all the flow is going through a single TRV-less radiator. However, a better solution in your case would be an intelligent pump - such as a Grundfos Alpha[1] - which reduces its speed when the flow path is restricted rather than increasing its pressure.

[1] See