Keeping house warm

We have a one-year old condensing boiler on the heating system. The boiler
has an external water-temperature selector dial. The system has a hall
thermostat.
If we need the house a bit warmer, is it more economical to turn up the
water temperature or the thermostat, or is the overall cost the same? To be
honest, if the thermostat works, I can't see why one would need to alter the
water-temperature.
Reply to
Budgie
I think I would only increase the water temp if the system was failing to meet the room temp set by the room thermostat - or the response time to get it to hit the desired temp was too long.
Personally, I prefer to have the radiators giving out a bit of warmth - rather than hitting the set temp and then going cold for a while.
I am sure someone will have the ideal solution (I do not have thermostatic rad valves yet - just a very sensitive room stat in the hall.
Reply to
John
For a given room temperature around the house the cost of heat loss through walls, windows and roof will be the same, no matter how you achieve that temperature. The difference between your two options will be how efficiently the boiler runs, that is how much of the heat you generate from the gas you burn goes into the water, and how much goes down the flue. The usual wisdom is that boilers run more efficiently at max. So better to crank the boiler thermostat right up and control the temperature of the house via the room stat.
Cheers!
Martin
Reply to
Martin Pentreath
The message from "Budgie" contains these words:
I am not a fan of hall thermostats* but they do do what it says on the tin. Leaving the thermostat set as normal and turning up the water temperature will make your boiler marginally less efficient and maybe get the house up to temperature quicker but won't otherwise effect the house temperature provided there is sufficient heat to eventually get the house up to temperature.
Unless you have separate controls for domestic hot water and space heating the boiler thermostat should be set as low as is consistent with hot enough domestic hot water. Only turn the boiler up further if the house doesn't get warm enough for the thermostat to function.
*
Why make the best regulated temperature in the house the place where it matters the least?
Neighbours with a hall stat use it only as an on/off switch and won't take the trouble to work out how to set it so that the house is at a comfortable temperature.
When my sister mentioned fitting a programmable stat to the gas boiler maintenance man during an annual service some years ago he even gave the ease in which the heating could be turned down on exiting the house as a reason for fitting the thermostat in the hall. Needless to say when I got round to recycling my first programmable stat it went in their living room.
Reply to
Roger
The message from Martin Pentreath contains these words:
An arguable point with conventional boilers but with condensing boilers lower is better. With a return temperature of above 55C (IIRC) there will be no recovery of latent heat by condensing the water vapour in the exhaust and the saving is progressive the further the return temperature is below 55C. I don't know how low you have to go to get the whole 10% saving but probably low enough to mean that in practice most condensing boiler owners never get the savings they were promised.
Reply to
Roger
I'll defer to you on that one Roger, and bear it in mind when I upgrade to a condenser.
Interesting, because I currently have oversized rads in most rooms. Presumably that will be a benefit with a condensing boiler, because I'll be able to match the rooms' heat loss, even running the boiler with a low return temperature, and I might even see my 10%.
Cheers!
Martin
Reply to
Martin Pentreath
TRVs are used for temp regulation in other rooms.
I put my stat in the hall because a) it is generally colder than the living room b) the living room has a gas fire c) the CH system is (sort of) set so that the hall is the last place to warm up fully d) other areas like kitchen and bathroom have too variable a temperature depending on when they are being used
Reply to
PM
The message from "PM" contains these words:
snip
Still begs the question though. You don't get as good temperature regulation with TRVs as you do with a good thermostat (or even with a crap thermostat).
snip
That doesn't matter at all.
Which could be a problem if you actually use the fire but with a fire you can't be looking for well regulated heat anyway. If you only use the fire occasionally you can get round the problem by having a second thermostat in parallel and TRVs on all radiators. When you want the fire on turn down the living room stat, set the living room TRV (from open), turn up the hall stat and open the hall TRV.
Should be easy enough to make it more balanced but does it really matter if the hall is too cold?
I personally wouldn't want a thermostat in either kitchen or bathroom but ISTM to make more sense than the hall. FWIW I have another programable stat in the main bedroom to control upstairs and a radiator off the bypass loop so my bathroom is always up to temp when the boiler is on.
Reply to
Roger
Most condensers will also modulate and hence set their own return temperature so as to work within the optimal range whenever possible. So the picture is probably not as bleak as you paint it.
Reply to
John Rumm
The message from John Rumm contains these words:
How low does the return temperature have to be before the full benefit (10.4%* theoretically IIRC) of the latent heat is received? ISTR this was touched on in a thread some time ago but I can't locate it.
*
The difference between the higher and lower calorific values of natural gas. The saving is rather smaller with oil (More C and less H). I am sure John knew that anyway but some of our readers might not be aware of why there is a limit on the potential savings from condensing boilers.
Reply to
Roger
It does if the living room holds its heat better than other rooms, or has other heat sources - like people - adding to the temperature.
Er yeah...that sounds less trouble :-)
No, but other rooms benefit as well. I want the hall to be the last place to reach temperature, because then when the room stat stops calling for heat all the other rooms are already at the correct temp.
Why wouldn't your bathroom be up to temp without the bypass loop?
Reply to
PM
Roger pretended :
We are well sealed up, carefully ventilated and well insulated. We have a gas fire in the living room which we never use (it's just there for emergencies), a hall stat and no TRV's fitted.
The way we operate it is that we generally leave most of the internal doors open, so the stat 'sees' the average house temperature. The living room and two of the bedroom radiators are turned off, rarely actually being needed.
Reply to
Harry Bloomfield
The message from "PM" contains these words:
snip
So you are content to fire up your boiler just to heat the hall, or to heat rooms that are unoccupied?
It's a bodge for people who just can't do without a real fire on highdays or festive occasions.
But to do that you have to rely on the uncertain nature of TRVs in the living room. I would rather have my living room at the temperature I want it to be without constant faffing around fine tuning the TRVs just because the weather has changed or the furniture rearranged.
It would be up to temperature less often. I have downstairs controlled by a programmable stat in the living room and upstairs by another in the main bedroom. Putting the bathroom radiator across the bypass loop means the radiator is functioning whenever the boiler is firing and even in summer when only the DHW is on. The radiator has a TRV (and the bypass loop an automatic valve) so the bathroom never gets too warm. I like a warm bathroom possibly as a reaction to those winters in the 60s when taking a bath meant a room with no heating and likely as not ice on the inside of the window.
Reply to
Roger
Below the dew point at about 54 deg C IIRC. Having said that you get some extra benefit from the larger primary HE fitted to most condensing boilers anyway, even if the return temp is higher. Many conventional boilers will have a flue gas temperature of over 200 deg C so as to ensure that condensing rarely happens.
The calorific value of the gas varies a bit according to its source can be as low as 37.5 MJ/m^3 or up to 43MJ/m^3, and that is dictated by the methane to ethane, and other compounds present. Hence the difference between gross and nett calorific values is not constant either.
Reply to
John Rumm
Set the wall thermostat to the lowest temperature that you are comfortable with. If the system fails to heat the house turn the boiler thermostat up, other wise try to find the lowest setting on the boiler that heats the house and water adequately.
Reply to
Ed Sirett
In article , "Budgie" writes:
You set the room stat to the temperature you require. If the water temperature is set too low, the room stat will call for heat all the time, but the rooms will never get up to temperature. If the water temperature is higher than needed, the boiler runs less efficiently.
The most economical setting is to set the water temperature such that the room stat never quite or just occasionally cuts out the heating. The problem here is that this temperature changes with outdoor conditions and it needs boosting if you are heating the house up from cold, so it would be a pain to set it accurately by hand all the time. Some of the more expensive boilers do this automatically, otherwise people set it higher than the most economical setting as a compromise against having to fiddle with it all the time. If the boiler also heats a hot water cylinder, then you would need to set the water temperature at least as hot as you want your hot water, unless your boiler has a separately controlled output for a hot water cylinder (one or two do).
Reply to
Andrew Gabriel
The message from John Rumm contains these words:
I am sure the thread I half remember maintained that condensation wasn't a step function. It only started at 55C (54 even) and increased as the return temperature was reduced still further.
After trawling through googles archive I eventually came upon this from Andy Hall in September 2005:
"One thing to realise is that the 54 degree dew point is not like finding the Holy Grail. On a condensing boiler, the efficiency improves with reducing return temperature. Above the dew point this happens at one rate with respect to temperature. It happens at a greater rate below the dew point. There is a graph on the data sheet of the Celsius boiler on Keston's web site which shows this. "
Which must be what I remembered.
Unfortunately I cannot find the referenced information on Kestons website.
That caused me to go back to my reference book which gives the LCV as 34.5 for North Sea gas and the HCV 38.5. Presumably your figure is HCV. More ethane would mean less water but it would surely take a major difference in the composition to materially effect the %age difference but then ISTM that it would take a major difference in composition to get such a huge range in CV.
Wikipedia would have us believe that raw natural gas is 70 - 90% Methane and 15 - 5% Ethane but "Before natural gas can be used as a fuel, it must undergo extensive processing to remove almost all materials other than methane" and "The gross heat of combustion of one normal cubic meter of commercial quality natural gas is around 39 megajoules (?10.8 kWh), but this can vary by several percent". 40.6 is about 4% above but 43 is 15%. IMO 15% is more than a little too high to be classed as several %.
I have had a look back through some of my gas bills. In recent years the CV has varied between 40.1 and 40.6 but back in 1981 when my reference book was still quite new (before 1981 the bill was in different units) the CV was significantly lower. Through the 80s it varied from 38.2 to 38.9. I wonder what cheap wheeze BG has hit on to cause the inflation in gas CV.
Reply to
Roger
Yup... I did find an interesting page somewhere that gave typical HCV's for the different producers. Ah, here we go:
formatting link
More ethane would mean less water but it would surely take a major
More ethane would also mean less carbon, and hence presumable less heat. Less water would mean less latent heat of vaporisation to recover.
43 is probably over the top in most cases.
I don't know, but I expect there is one ;-)
Reply to
John Rumm
The obvious solution is to reduce the return temperature even further so that the CO2 condenses. Don't forget, you heard it here first.
Reply to
Mike Barnes
The message from John Rumm contains these words:
formatting link
formatting link
Wikipedia: Heating value"
Wikipedia is becoming ubiquitous but how far can we trust it?
I wonder how it is that Netherlands Natural Gas is so far below even the worst of the rest.
I didn't have a clue about the relative exothermic properties of Carbon and Hydrogen combustion but the Wikipedia link gives the heating value of Hydrogen as 286 KJ/MOL and Carbon as 393.5 so surely more Carbon means more heat. That would also explain Algeria's position out of step at the top of the table with 42 MJ/m^3 if they are using the gas with almost no processing to take out the heavier fractions.
Yes but seeing H/C in Methane is 4/1 and and in Ethane is 3/1 the difference would only be marked if ethane was present in larger quantities than it is even in raw natural gas. Wikipedia (yet again) referring to the cited list of Natural Gas values doesn't see much variation even with a 20% difference (or 26% looking at it from the other end) across the spectrum"The lower heating values of the above natural gases are about 90 percent of the higher heating values."
Reply to
Roger

Site Timeline Threads

  • Does anyone know who makes this for Wickes ?and availability of spares now and...
  • next in

    UK Do-It-Yourself

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.