Hot water cylinder cools by 8 degrees in 24 hours - normal ?

2

Comments

  • [Deleted User]
    [Deleted User] Posts: 0 Newbie
    Name Dropper First Anniversary First Post
    coffeehound wrote: »
    What is your tank's peak temperature? OP's appears to be only 53..

    I don't have one, the calculation was for the OP.
    WobblyDog wrote: »
    Thanks, I hadn't thought of doing a thermal conductivity calulation. I've just done one, and I get a temperature drop of 8.3 Celcius over 23 hours. I'm a bit surprised that so much heat is being lost through the insulation, I thought convection around the loop through the boiler might be the biggest problem. Time to buy an extra insulated jacket maybe, but also possibly turn up the thermostat to avoid legionella.
    My input numbers were
    Height = 1m
    Diameter = 0.42m
    Insulation thickness = 0.04m
    Conductivity = 0.03 W/mK
    Air temp = 25 Celcius

    Based on those data, I get a temperature drop of about 4.2C.

    Are those graphs of yours from a data logger?
  • WobblyDog
    WobblyDog Posts: 512 Forumite
    First Anniversary First Post
    edited 15 July 2017 at 9:03PM
    jack_pott wrote: »
    I don't have one, the calculation was for the OP.



    Based on those data, I get a temperature drop of about 4.2C.

    Are those graphs of yours from a data logger?

    Having just checked my numbers, I had the area calculation wrong. I now get a 3.9 Celcius drop due to loss through the tank insulation in 23 hours. I think I need to buy some pipe insulation as well. The graphs are from a Raspberry Pi, and a bunch of DIY Python and Java.
  • silverwhistle
    silverwhistle Posts: 3,791 Forumite
    First Anniversary Name Dropper First Post
    An observation not based on any figures at all, but I heat my hot water using an immersion and excess energy from my PV panels using a diverter which identifies when there is spare energy available.

    My tank has integral insulation but the other day I was in a well known chain for other reasons and decided to add a £10 insulating jacket to my order. I've fitted it and the airing cupboard is now a lot cooler, and (anecdotally) I seem to be losing less heat. I've a monitor which tells me how much I've put into the tank each day, and that appears to be reducing.

    Gas boilers are a fairly inefficient way just to heat a little water. My motivation was more to extend the period during which I don't need to use the boiler at all (currently mid March - end of September), but additional insulation should help your situation as well.
  • Geoff1963
    Geoff1963 Posts: 1,088 Forumite
    Instead of lagging the cylinder, why not lag the inside wall of the airing cupboard, then it will run warmer ? If you don't use the airing cupboard, you can fill it with insulation.
  • Geoff1963
    Geoff1963 Posts: 1,088 Forumite
    Check the temperature of the pipes. Any that are colder as they enter the tank, is probably a return convection.
  • FreeBear
    FreeBear Posts: 14,617 Forumite
    First Anniversary First Post Name Dropper Photogenic
    silverwhistle wrote: »
    Gas boilers are a fairly inefficient way just to heat a little water.

    Agreed. I only use a couple of litres of hot water each day. Much more efficient to boil a kettle for that amount. Also have an electric shower, and only fire up the gas boiler when I want a tank of hot water for a bath during the summer months.
    Her courage will change the world.

    Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
  • stator
    stator Posts: 7,441 Forumite
    Name Dropper First Anniversary Combo Breaker First Post
    My tank is from the 90s. It has some foam lagging and an extra jacket that I fitted.
    After 24hrs I would not expect the water to still be hot or even warm, so 45c would be good.
    Changing the world, one sarcastic comment at a time.
  • ComicGeek
    ComicGeek Posts: 1,539 Forumite
    First Anniversary First Post Name Dropper
    Cylinder loss of 1-1.5 kWh per day is actually really good, and comparable with new cylinders. If water usage is very low then you definitely need to use the immersion during non heating months, it's so inefficient using an older non condensing boiler to do just a small load.

    Ideally you would insulate the primary pipework from the cylinder all the way back to the boiler, but that may not be possible in terms of access. Even just doing the first 1m length from the cylinder (which is probably accessible within the cupboard would have an impact.

    But at what point is it not worth doing any more, as you won't get a return on your investment. Sounds like you should ultimately get a condensing combi boiler as a replacement whenever you need to replace the boiler, so any payback period for additional insulation needs to take this into account.
  • ComicGeek
    ComicGeek Posts: 1,539 Forumite
    First Anniversary First Post Name Dropper
    But you should also be heating the cylinder up to at least 60 degC once a week to kill any nasty bugs etc. Particularly important if you're not using enough hot water each day to turn over the cylinder.
  • dggar
    dggar Posts: 670 Forumite
    First Anniversary Name Dropper First Post Combo Breaker
    WobblyDog wrote: »
    My boiler is using about 8kWh of gas per day to put about 1.3kWh into the hot water cylinder. Even allowing for heating up the boiler and 20 metres of 22mm pipe, that seems inefficient. Maybe I ought to get it serviced.


    Have you estimated the input of kWh using the electric immersion heater (I assume it should still be approx 8kWh).


    If you have how does the cost of 1kWH of gas compare with 1kWh of electricity for your energy tarriff.
This discussion has been closed.
★ ★ ★ Meet your Ambassadors

Categories

  • All Categories
  • 343.2K Banking & Borrowing
  • 250.1K Reduce Debt & Boost Income
  • 449.7K Spending & Discounts
  • 235.3K Work, Benefits & Business
  • 608K Mortgages, Homes & Bills
  • 173K Life & Family
  • 247.9K Travel & Transport
  • 1.5M Hobbies & Leisure
  • 15.9K Discuss & Feedback
  • 15.1K Coronavirus Support Boards