I had a new CH system fitted in my Victorian Semi this summer, and have only recently began to try it in anger. The insulation of the house is not great i.e. no DG, thin loft insulation etc. my question is this:
Should my C&M Condensing boiler be running constantly? It fires up and reaches and maintains temperature quickly enough (80C outlet), but after 6 hours the house has only reached around 17C, with a set point of 20C!
Would it be a good idea to leave the heating on constantly rather than switching on/off via a room stat?
From what start temp? Stone cold after a period of non-occupation or just what it falls back to each morning?
If it takes this long each day then it sounds like you don't have enough radiator capacity in the place. Are all the rad valves fully open where appropriate and bled of air? Are the rads getting properly hot? They should be just about too hot to touch for more than a second.
Is the boiler pump on a high enough setting? If it's too low the water will be cooling down too much as it travels the circuit. Usually there's a two or three position switch. Try whacking it up a notch.
I'd say any house that has the appropriate boiler and radiator capacity and everything working right should get to temp in a couple of hours max even from very cold.
No. The room stat doesn't slow down the time the house takes to get to temperature.
Sounds like you have enough losses that you may have to.
The wind we had two days ago made it barely possible to keep up with heat losses here. Its better at -10C on a still day than 3C and a 30mpjh wind,is this house..bloody silly BCO and his ventaliated concrete floor..
The room stat is set to switch on/off twice a day i.e. on at 6am off at 8am, on at 4pm off at 11pm. The house cannot be warming up more than around 7C during these times.
I haven't balanced the rads yet as i'm assuming this was done on installation. Each rad (apart from 1) is fitted with a TRV which are all fully open. Also, the room stat is in the coldest part of the house - as I assume it should be - and admittedly this room is perceptively colder than most of the other rooms as the front door leads into it.
I have bled the rads and each one is getting fairly hot, although i can keep my hand on most for a good few seconds. I'm thinking you may be right with the rad capacity :-(
IIRC the pump is on it's highest setting, but I will check when I get home.
I may have mislead you here. I mean would it be a good idea to leave the stat to control the boiler 24/7, rather than have it on a timer - economically wise?
If the fabric of house has been left to get very cold, it will take some time to get it up to temp - I remember when I first fitted mine. Try running it continuously until you get to the set temp then switch back to the timeswitch for occupied hours or whatever.
Its not clear as to whether the rate of heat increase is so slow because the rads are undersized - in which case the boiler should be cycling on and off - or whether the boiler is barely adequate. My boiler goes on and stays on - hard on - for 4-6 hours to get the underfloor temperatures up. Then I get a half to one degree overshoot, before it settles back slowly, and comes on a couple of hours later as the temp dips below that stat point.
If the boiler is barely adequate the ONLY way you WILL be able to keep warm is 24x7 operation, never mind the cost!
If the rads are inadequate, you may still need to go for a 24x7 operation, but the boiler should cycle a lot.
All other things being equal, a timed operation should be cheaper, as the house is cooler = less heat loss - when not 'in use' BUT things are not always equal. Boilers may become inefficient, or more efficient, under short duty cycles or modulation.
I haven't personally noticed much difference either way really.
I have gone back to timed simply because the sound of the boiler firing up at 4 a.m. wakes me up...
I will try running the heating continuous for a few days and see what happens.
I wouldn't have thought the boiler is undersized as it is sitting happily at 80C outlet temp, just ticking along on lowest flame - it is a *fairly* small 3 bed house with 7 rads and a friend has exactly the same boiler in his large 1930s house. All rads are boiling hot and stat still not reaching 20C set-point, which suggests to me that they may well be underated.
I think you definitely don't have enough rad capacity. My similar small 3 bedroomed, solid wall, no DG semi-detached also struggled to get up to temp or reach a sufficiently high temp with 9 rads plus a gas fire in the lounge. It's all kind of academic now as the boiler has been broken for a couple of years and I've been managing through the winters with just the gas fire and an electric one in the kitchen. Not exactly fun but worse things happen at sea.
You can use this
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see if the rads in each room are big enough. There are plenty of other calculators for either the boiler size or the rads if you Google.
The biggest factor by far is the insulation level. Cavity walls plus insulation, DG, draught proofing and plenty of loft insulation can halve your heat requirement.
Virtually all modern boilers are modulating so would just keep running at a lower output rather than cycling. You would need to time the meter to see whether it was running at full power, unless the boiler has a way of showing this.
He is absolutely right if you truly have 80C flow form the boiler (not just a requested idea). Then every radiator should be hazardous if they aren't then the system is wrong.
If you can leave your hand on the flow pipe from the boiler for a second then you don't have 80C flow.
I remember going to my parents holiday apartment last winter. It is a middle floor apartment (or you can call it a flat) with concrete ceilings and concrete floors. The flat above was empty due to a sale and the flat below was empty due to a death. There was no heating on any of the 3 floors in the month up to me arriving and it was below zero outside. The heating soon heated the air but it was nearly 24 hours before the floor and walls reached reasonable temperatures. You could feel the cold on your feet and my laser thermometer showed it all. I fitted a frost stat whilst I was there as a precaution.
In article , snipped-for-privacy@southernwater.co.uk writes
Bing!
It is very common for (poor) installers not to balance systems where TRVs are fitted, arguing that the TRVs balance the system when the demand temperature is reached. This is wrong for 2 reasons, 1) all systems need balanced otherwise the system will not warm up in a balanced manner and 2) if you override the room thermostats (the TRVs) as you have by setting them to max then an unbalanced system is will never come into balance.
If the system has not been balanced then hot water will flow via the path of least resistance back to the boiler causing the return temperature to rise quickly which will case the boiler to modulate down thereby producing less output.
Modern boilers have a huge output so I'd be very surprised if there was insufficient output to heat even a very lossy house.
I suggest you perform a full balance per the group faq and set the TRVs to sensible levels, I'd be surprised if they need to be set higher than
3/5.
If you don't have the necessary thermometers to do a proper balance then do it by hand, as a very rough guide (and with TRVs fully open), the flow pipe should be unbearable to hold in less than 5s, the return should be bearable for 20s or so. Balance the system properly when you can.
The message from "Dave Baker" contains these words:
ISTR that in the days when I only had a frost stat to rely on getting my stone walled hovel fully up to temperature after going cold in winter was closer to 2 full days than to 2 hours.
A modern house with very little mass inside the insulation gets up to temp very quickly.
If however you have stome walls or massive chimneys or even a large slab of concrete for a floor, there is a HUGE thermal store.
My dining/living room area is solely heated by UFH or two large open fires. At night we leave it at 20C with a warm chimney. No heating comes on. By the morning its down to 17C if its 5C or less outside.
It takes the WHOLE afternoon and early evening.. to get back up to
19C..with UFH running flat out at its measly 50W/sq meter output.
In hot summers I see 23C +- 2C over the day,night cycle with no heating. That's with outside air temps up to 32C or more. dropping to maybe
14-15C at night.(IIRC)
If you have sucha massive thermal store, it makes very little difference when the heating is on. It will take ages to heat and ages to cool.
I think it may be a combination of all the factors mentioned above. The house has several large chimneys and a combination of concrete/ suspended floors, and cavity/9" single walls. In addition to this IIRC the installer didn't balance the rads as I was at home when he was comissioning it! I will have a go at balancing them at the weekend.
Just as an update, I left the heating on all day today and it was a toasty 20C when I got home from work so I'm thinking the thermal store theory may be most relevant here. Lets see how it gets on tomorrow with being back on timer!
I'd check the system balance, if all the flow is going through just one or two rads then this is what will happen. The boiler sees the rising return temp and modulates down.
That isn't what you said earlier:
"I have bled the rads and each one is getting fairly hot, although i can keep my hand on most for a good few seconds."
OK, you need to measure the height and width of each radiator, and work out the area (just h x w of one face - not the total surface area). Then apply the following approx rules of thumb, depending on the construction:
Single rad without fins: 1280 watts/M^2 Single rad with fins: 2000 watts/M^2 Double rad without fins: 2170 watts/M^2 Double rad with single or double fins: Dunno - but work it out from radiator catalogues
Note that the above figures are based on a Delta-T (the difference between mean rad temp and room temp) of 60 degC. In practice, your CH will run at a lower Delta-T than this, and you need to downrate the radiator capacities as follows:
Delta-T % of 60 deg value
60 100
55 90
50 80
45 70
If you have a conventional boiler, a typical Delta-T is 55 (Flow 82, return
70, mean 76, room 21). If you have a condensing boiler, your Delta-T value is likely to be less than this.
Are you measuring the temp in the rooms that you occupy? If you are relying on the 'click point' of the thermostat and this is on a cold wall then it could be misleading you.
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