Any heating guru's in?

I have posted this elsewhere on the net, but thought I would ask here as the quality of the advice is generally better here.

We've lived in our current house a year now, and I must admit that we didn't really get to know our heating and hot water system properly last winter, and all summer it has been on for water only.

So, I am looking for advice as to how to set this system up to get the best balance of efficiency but also usability please.

The system consists of:

A Glow Worm 18HXi system boiler.

A Horstmann H27XL controller

with 2 x 4ft double rads in the living room downstairs, 1 x 3ft single rad in each of the two bedrooms, and a heated towel rail rad in the bathroom, and a hot water cylinder stored in an airing cupboard.

Each of the rads, with the exception of the towel rail one, has a TRV, all of which seem to work fine.

The heating side, I think we pretty much have nailed - periods when we are in, run the heating with the TRV's set to the desired room temp (the controller allows for up to three timed periods per day, and allows different timings to be made for different days of the week) - am I correct in assuming that its best to run the heating fairly constantly to maintain temperature rather than have a warm/cold/warm cycle?

The water, I just don't get (mainly because I am used to 'on demand' systems. We've not yet been without hot water (except when we use loads of course), but I am not convinced that I am heating it efficiently. At the moment, its set to come on during the night and heat for about an hour, and then again in the afternoon for half an hour or so to boost it before we get in from school/work - weekends have an additional period in the middle of the morning, as we tend to use more at weekends.

Now, my understanding of the system is that the controller switches the boiler on whenever there is a demand for heat, regardless of whether that heat is to heat water or to heat the house, and then there is a three way valve (recently replaced) that decides where that heat is directed?

Does that mean that I can (or should) be heating the water whilst the heating is on? Or is that inefficient?

If I did set the two to come on and go off together, would the hot water simply reach a temperature and then stop taking heat from core in the tank, allowing that heat to continue round the system into the rads?

Or should I be running the two separately in cycles? If so, how long does it take on average to heat a cylinder of cold water?

 

The Three Port Valve is the key, basically you can set the hot water to come on (via the controller) at peak times - then the boiler only fires up when your hot water tank temp sensor triggers it. The 3 port valve directs the heated water from your boiler to warm up the tank. When the tank temp sensor finds that it is warm enough it shuts down the boiler.

For heating the rads, the room thermostat will trigger the boiler whenever the temp goes low enough. In this case the 3 port valve switches to direct heated water from your boiler straight to the rads.

If both hot water and radiater heating is needed at the same time, then the 3 port valve will go to the mid-position directing heated water from your boiler both ways.

So your boiler will only come on when something actually demands it (assuming everything is wired up correctly).

Hope that makes sense.

BTW: My cyvlinder heats up from cold in just a few minutes, it shouldn't take long for a decent boiler to maintain the desired temp.

 

Makes perfect sense, thanks John - the only thing is, I don't think that there is any sensor in the water tank. It seems to be set up so that the controller tells the three way valve what to do depending on what mode its in:

- if heating, the controller switches the boiler on and then moves the three way valve to the relevant position; if water, the same thing happens, but the controller moves the valve to water, and I 'think' if both are on, then its the same but the heated output from the boiler is allowed to flow through rads and hot water tank at the same time.

I was kinda working on the premise that heat transfer would only continue to take place within the cylinder until the water reached temperature, and then all that would happen is the heated output from the boiler would carry on passing through the cylinder and then back into the heating system,and therefore it wouldn't be possible to overheat the hot water? Hope that makes sense?

 

On your water tank (hot water cylinder) there should be a thermostat, usually its strapped on around the tank and will have a dial you can adjust for the water temp. It might be hidden underneath your tank's insulation jacket, but there should be a cable going to it which might help you trace it, the thermostat should be approx 1/3 way down from the top. If you don't have that then it's a system I've not heard of (but I'm not a 'guru').

The boiler will have an internal thermostat so that if the returning water is getting too hot it will shut off the boiler. This is really only for safety and shouldn't happen unless one of your thermostats fails (i.e the tank or room thermo).

 

Well, I've learned something now - thank you John There is indeed a thermostat, about 1/3 way down the cylinder, tucked around the side, and currently set to 60 degrees

So, the best bet with this then is to decide when we are likely to want water, and have the heating timed to on during those periods, then if the water temperature drops it will automatically trigger the boiler and the our hot water will be as near to 'on demand' as can be with a system like that?

As for the heating, we don't have a room thermostat at all, only the TRV's on the rads - these seem to work quite well, as the rads can be heard shutting off and coming back on if you listen carefully.

I think we kinda fell into a trap last year, which led us into having the rads turned up higher than we should have - we had them all set to 5 or 6 so they would come on pretty much full tilt, warm the house up, then the system would go off, the house would cool and then the whole cycle would repeat - we even had to have an hour or so in the middle of the night on the really cold nights which led to us being too cold, then too warm, then too cold again.

I'm wondering now if it would be more efficient (it would almost certainly be more comfortable) to have longer periods of lower heat, so for example from 5pm until 9pm and then again from 4.30 until around 7.30 in the morning?

If we then hit a really, really hard spell, we could put the heating on constant overnight and just let the TRV's take care of it all?

 

Yes that's just what I do

OK so you have no room thermostat, it's not a set-up I know about but I'm sure it will work just as well. So you use the TRVs to control each rad and then you use your controller to set the on/off periods. In answer to your question, Yes, longer periods at lower heat would be better I would think. It's something you have to keep fine tuning I reckon, I do with mine, keep adjusting the TRVs. For instance in the spare bedroom we turn the TRV right down when it's not in use.

You can get TRVs with battery operated timers for even better control, but they are expensive and I already have too many clocks to fiddle about with on daylight saving changeover and I bet they go wrong more often.

 

Thanks

I've came up with what I think is a plan for this winter then - does this look sensible?

Chilly weather:




Cold weather:



FMI Freezing weather:


The controller allows three spells each of heating and water, hence the CH 1, HW 1 etc.

 

Blimey fc I thought I was the only one with spreadsheet OCD (no offence intended) That's a good idea to plan it out like that, obviously the times have to fit in with the fc household lifestyle. Can't say I ever change the on/off times on our system, we just let the thermostats and TRVs handle it. We always have our heating on till 11pm ish till we go to bed, if it's cold outside the boiler comes on more often.

I wonder if your house is leaking heat, do you have cavity walls? We have cavity wall insulation here, that made a massive difference to retaining heat - have you got it? I heard some radio adverts last week saying our council are giving it away free right now. It cost us £400 a few years ago but paid for itself within a couple of years.

 

The controller is in the cupboard in with the water tank, so to program it means a session on ones knees and I thought the easiest way to do it was to plan ahead, print it out, and then just follow the plan.

We tend to get up around 5am, and are all out the door by 8am, returning home by 3.30pm, popping out again at 5pm until 6pm and then that is us in for the night, hence going for the timings above.

The house doesn't seem to leak a lot of heat - certainly not when compared to our old house anyway, although I believe it does have cavity walls. As I rent, I'm not sure how receptive the landlady would be to getting the insulation done, as many landlords don't like it in case it stops airflow and causes damp. I do wonder if there is enough rads though - there is no rad in the kitchen for example, which is completely open to the living room which can chill the living room quite a bit. There is also no heating in the front porch (not that you'd want a lot), and there is only a glass panelled door between the living room and the porch.

The living room is also open plan onto the staircase, so the heat rises and you end up with the top of the house roasting whilst the bottom floor is still chilly - again, this is what led me to think that longer periods on lower TRV settings might be better as, given time, the overall temperature would stabilise a bit if you know what I mean?

 

First of all, I must emphasise that I'm no expert in any way but I did do a lot of research into this type of thing some years ago - and picked the brains of some friends who were heating engineers.

I'm a bit puzzled that you don't have a room thermostat somewhere . It's the normal way to run a system that has TRV's. You have the TRV's set in each room to the temp you want and have the main (room) thermostat set to trigger the system at the general temperature you decide on.

The usual place for the room thermostat is in the entrance hall (convenient for when going in or out of the house. You should not have a TRV on the rad where the thermostat is. If you don't heat the hall then you normally have the thermostat in the lounge.

Having the thermostat makes life a lot easier from a timer point of view. You have each TRV set just as you want it for the individual rooms. The timer can be set to keep the boiler on from just before you get up until just before going to bed (so no complicated changing of timings). The thermostat is your main controller. You set that (usually a simple dial) as you want it. So, for instance, you set it at 70F when you go to bed (the heating will be off anyway because the timer has switched it off) and, in the morning, the timer will bring the heating on before you get up and the thermostat will allow the temp to rise to 70F.

When you leave the house you can just flick the thermostat to 60F (or any other temp you want) and the system will remain active but not operate until the temp drops below the setting. This will keep the chill off the house and when you get home you just flick the temp up to whatever you want.

We never change the settings on the timer. If we go away in the winter (we have sometimes been away for a month) we just set the thermostat to keep the chill off the house (50F). This didn't cost us very much but seemed to keep the house in better condition. In the hot weather the timer is still kept the same and the thermostat is left at 60F - so the heating never comes on unless we get a sudden drop in temp.

Re hot water - We keep that set to be on permanently (except when we're away) and if the hot water cylinder is insulated efficiently it only fires up when some hot water is used and the cylinder stat notices a drop in temp. The experts say that the cylinder stat should be set at 60C. With an efficient boiler you shouldn't run out of water. We quite often have a shower and bath (I prefer showers but Mrs S doesn't) at the same time and don't run out of hot water.

Most modern timers also have a 'Boost' button will bring the heating on for an hour (if it's off). This is handy on very cold nights if you want to stay up longer than your normal timing. You leave the timer setting as normal and just press the 'boost' button. You can do this as many times as you wish.

 

Thanks Shiney - that all makes perfect sense to me, and that is more like the system I am used to (except that I am used to on-demand hot water from a combi boiler) - we definitely don't have any room thermostat anywhere, although I am considering fitting one if its not an overly complicated process to wire it in alongside the existing controller. Getting the wiring downstairs for a thermostat would be a pain in the rear, so it would have to be upstairs somewhere (I am thinking on the landing where there is no heating nearby);

Not sure how I could connect it though, as there is only one power lead that goes up to the boiler which is for water and heating, so its not as though I could have the controller running as on, and then interrupt the mains supply to the boiler with the thermostat because that would result in there being no hot water unless the room temperature was low enough?

I want to move the existing controller anyway, as its in such an inconvenient place in beside the hot water tank - it does have a boost button which will give us an hour for one press or two hours for two presses, and we can do that for either the heating or the water.

I have to tread carefully with this one though, I rent this property so can't go doing anything too radical (having said that, my landlady is generally accommodating providing things are done correctly)

 

Just a reminder that you are not supposed to do the electrical work yourself unless you get it signed off by an electrician that can give you a Part P certificate.

 

I have a good electrician who does it for me, but he also charges quite handsomely, also part of the reason for my desire not to get too radical - I don't really fancy spending hundreds on a house that isn't mine; whenever I am getting him to do something, I tend to do the donkey work such as running the cables etc and planning out what is going where, and then get him to do the actual connecting up bit for the sake of a cert.