Condensing boilers – heating hot water – timed or permanent?

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  • Condensing boilers – heating hot water – timed or permanent?
  • Premier Icon yoshimi
    Subscriber

    I tend to have the hot water heating come on twice a day for 1.5hrs each time.

    I was talking to a friend over the weekend who also has a condensing boiler and he’s been told that its much more efficient to have the water heating on permanently.

    Any experts like to share their thoughts?

    nealglover
    Member

    Presumably you are heating the water in a cylinder rather than as it’s required, and if so, then it would depend on the amount and the frequency of use, and the level of insulation and heat loss from the cylinder.

    I suspect your method would be better though, as cylinders don’t tend to be perfectly insulated, and average peak useage would be several hours apart.

    Premier Icon footflaps
    Subscriber

    Our heats twice a day, once before we get up and then at 9am to re-heat the HW tank after morning showers.

    nealglover
    Member

    Our heats twice a day, once before we get up and then at 9am to re-heat the HW tank after morning showers.

    If people are in and using hot water during the day, that makes sense.

    For an “average” household it wouldn’t so much.

    sharkbait
    Member

    Why does the fact that it’s a condensing boiler matter? Hot water production is more efficient when the heating is also on so I’d go for timed.
    Read on the [government] energy whatever website the other day that it’s better to keep heating on constantly rather than timed is a fallacy and uses more fuel.

    trail_rat
    Member

    id argue that it depends on the construction of the house and the type of heating controller sharkbait.

    My heatings “always on” but only if the temperature in the house drops below 14 degrees. – reality , it never comes on outside of the times i tell it to come on to heat the house to 18.

    our old house was a nightmare , if you let it get cold (which it frequently did) it was 6 odd hours before it was back up to temperature thanks to the lovely thick stone walls.

    in any modern house that wouldnt be an issue – just have to accept it as one of the downside to having an old stone house thats not made of balsa wood and duckspit.

    nealglover
    Member

    Read on the [government] energy whatever website the other day that it’s better to keep heating on constantly rather than timed is a fallacy and uses more fuel.

    There is no way anyone can make that statement without knowing more about the individual property in question.

    Premier Icon footflaps
    Subscriber

    our old house was a nightmare , if you let it get cold (which it frequently did) it was 6 odd hours before it was back up to temperature thanks to the lovely thick stone walls.

    Only 6 hours! My parent’s cottage has 3′ thick stone walls and is set into the back of a hill. Takes about 48 hours to get above 15C in winter!

    Premier Icon just5minutes
    Subscriber

    I used an app called kWh on iphone to track gas usage and based over several months of data it’s consistently (to my surprise) a lot cheaper leaving hot water set to permanently on vs. timed – the volume of gas used has gone down (when the heating is turned off) by 3/4.

    One other thing that also made a significant difference was turning the hot water temp down from 70 to just under 60 degrees.

    Premier Icon geoffj
    Subscriber

    One other thing that also made a significant difference was turning the hot water temp down from 70 to just under 60 degrees.

    Careful you don’t end up with legionnaires disease or some other nasty.
    Once a week to 60+ should deal with it though.

    Premier Icon just5minutes
    Subscriber

    Good point Geoffj

    Premier Icon totalshell
    Subscriber

    gas engineer here so this is my advice.. start at your 1.5 hours twice a day and work down to a time that gives you enough hot water.. time those on periods to be the same as when the heating is on so you only heat the circulation water once..

    quick analogy .. do you have the kettle switched on all day just in case or just when you want a brew.. the savings demonstrated above will be purely as a result of reducing the temperature of the water in the tank i think you can go as low as 58 to avoid the nasties..the best way not to use energy is too turn it off not have it on all day..

    a hot water in a cylinder left to stand even lightly insulated will be hand hot for at least 3 days..

    Premier Icon yoshimi
    Subscriber

    totalshell – against you advice but I thought I’d try it anyway and found the following…

    I have switched the programmer unit to be on constantly and set the dial thermostat on the hot water cylinder to 60deg C.

    Once the hot water has reached 60deg the boiler/burner switches off but the pump attached to the cylinder still runs. It never stops running. I would have thought that when the set temperature is reached the pump should stop. Is this a fault?

    Premier Icon jambalaya
    Subscriber

    Hum, never heard the on-permanently advice before.

    If you are just a couple then heat on demand boilers (or whatever they are called) are increasingly popular. Where they a fall down is a larger house where you want to use two showers at the same time.

    The best way to save money on heating is to turn the themrostat down and wear more clothes.

    trail_rat
    Member

    the question that hasnt been asked here is .

    has your friend got a combi boiler – i do and it rarely kicks in but it is “always on”

    if you have it set to maintain 60 degrees in a remote tank and its the boiler controlling that – it has to keep pumping to monitor the temperature in the tank….. sounds inefficient to me compared to the combi.

    “If you are just a couple then heat on demand boilers (or whatever they are called) are increasingly popular. Where they a fall down is a larger house where you want to use two showers at the same time.”

    only if you have spec’d to your heating and not your water usage.

    my parents and me both have combi boilers that dont bat an eyelid at two showers going. my last rental had a pokey we combi that couldnt run a lookwarm bath in an hour.

    Premier Icon yoshimi
    Subscriber

    Nope, my friend has a condensing boiler like me with a remote tank.

    The thermostat is attached to the tank itself so I don’t see why it has to get pumped around.

    For the record, I’m not convinced leaving it on all the time is the most efficient way of doing it, just feels wrong. But after a bit of research I can’t find a straight answer so thought I’d try for a short while and monitor the consumption. I know this will hardly be scientific but should give me a better idea.

    nosemineb
    Member

    My hot water tank is set to 45.. will i die? We dont drink from the hot tap though.

    Premier Icon footflaps
    Subscriber

    Most traditional (old style) CH systems power the pump and boiler in parallel off the controllers (Thermostat and/or timers). So the pump runs the whole duration of the allocated ‘on’ period, where as the boiler can switch itself off when the returning water is above a certain temp.

    Running a pump is wasting 200Ws or so as well as cooling the HW tank down by distributing it’s heat along all the pipework to/from the boiler.

    crofts2007
    Member

    I’d also agree with the analogy of the boiling kettle theory, wastes energy topping up the heat regularly rather than in one hit.

    I run my water before the heating is on, as it reduces the time taken to heat the radiators due to the dhw tank taking the equivalent of two to three radiators to heat, but do agree that it is more efficient to run both together once the heating has warmed up some.

    The pump running on will probably either be the bypass cooling loop on the boiler is not set correctly and the boiler is running the pump on until the boiler core is low enough or one of the diverter/zone valves is sticking in an open position, backfeeding the pump. It is down to how the system was wired when installed.

    Premier Icon footflaps
    Subscriber

    Old systems, with a separate pump, just power the pump the whole time CH or HW is on – very wasteful, but all you could do with basic systems.

    Premier Icon yoshimi
    Subscriber

    Modern, well insulated house built in 2008 with Condenser boiler, hot water tank, programmable control panel in utility room and simple dial thermostat in the hallway.

    My old regime:

    Hot water Cylinder set at 65deg.C
    Boiler set to maximum (no idea what that temp is)
    Hallway room thermostat set at 24deg.C

    Heat Hot water cylinder from 4am to 5:30am
    Heat Radiators from 5:40am to 7:20am

    Out all day at work until I return home at 6pm

    Heat Hot water cylinder from 3:50pm to 5:20pm
    Heat Radiators from 5:30pm to 8:30pm

    I suppose my next question – based on the above, is it better to have both hot water cylinder and radiators heating at the same time but for a longer period as the time heating each will be lower?

    harrisp
    Member

    I think you may misunderstand what a condensing boiler is.

    nealglover
    Member

    I think you may misunderstand what a condensing boiler is.

    Based on what he said, I can’t think why you would think that ?

    (I think you may be misunderstanding actually 😉 )

    Premier Icon paladin
    Subscriber

    nosemineb – Member
    My hot water tank is set to 45.. will i die? We dont drink from the hot tap though

    Legionella bacteria only really a problem if you inhale it. This would be from air conditioning units or possibly shower heads.

    harrisp
    Member

    I can’t quote for some reason, I was referring to yoshimis response to trailrat asking if his mate had a condensing boiler.

    I am not confused in the slightest about what a condensing boiler is.

    Premier Icon footflaps
    Subscriber

    Legionella bacteria only really a problem if you inhale it. This would be from air conditioning units or possibly shower heads.

    Our work shower has been put of action for months due to finding Legionella bacteria in it. For some reason it is taking 6 months to clean it out…..

    Premier Icon yoshimi
    Subscriber

    Harrisp – care to elaborate? I’ll take any advice I can get

    Premier Icon Tiger6791
    Subscriber

    We’ve got some German sealed system malarkey, massive tank, set back curves, weather detector on the outside of the house, not sure how it works but I dare not touch it. This thing is more complicated than a woman.

    Ours fires up for 30 mins each day at 6am
    And for 2 hours on a Sunday

    That provides enough water to heat, shower, bath 4 of us. If we have guests the hot water can run out so we must be pretty near efficiency.

    Premier Icon yoshimi
    Subscriber

    Bloody hell Tiger, that does sound efficient, I want that!

    Premier Icon Tiger6791
    Subscriber

    It’s some Vaillant EcoTec weather compensator sealed system with a tank.

    No thermostats in the house just TRVs on the rads.

    Works really well though, as much as you can be impressed with a boiler I’ve been impressed with it.

    Completely different set up to our old Combi boiler!

    Premier Icon cr500dom
    Subscriber

    We have a Modern (Late 2009) mid Terrace 3 storey townhouse

    4/5 Bedrooms.

    Modern (Glowworm I think) Condensing combi boiler with internal tank.

    We were running hot water on constant and heating on twice a day, hot water is set to 67deg from memory.

    We have now switched to running HW twice a day instead of constant and its definitely cheaper

    nealglover
    Member

    I can’t quote for some reason, I was referring to yoshimis response to trailrat asking if his mate had a condensing boiler.

    Fair enough, there were several hours, and several posts, in between your post and the one to were apparently replying directly to.

    I am not confused in the slightest about what a condensing boiler is.

    Also fair enough, although as above, the way you posted made it look like you were.

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