Energy myth-busting: Is it cheaper to have heating on all day?
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Not sure what this has to do with heating. Did this post end up in the wrong place?I see that in 50+ Overseas Travel Tips Martin has fallen for the old chestnut of TVs take loads of power in standby. New TVs do NOT. The EU brought in a rule years ago that TVs had to draw less than 1W in standby. If you still have an old CRT TV then this might be true but any flat screen TV no.
And to put that into context 1W would be 1 unit, say 15p, in 1000 hrs, which roughly 1 month. Not really a significant saving is it.0 -
I want to add another caveat to this one. It depends how much hot water you need.Should I use an immersion heater to heat water, or oil-fired central heating?
Generally, using oil for hot water is cheaper, due to the higher average cost of electricity. However, if you're able to use a lower rate electricity tariff (such as Economy 7, where power is cheaper at night) at the right time, it can work out more cost-effective. This is also dependent on the efficiency of your central heating system.
In my case the immersion coil is a side entry model, positioned in the top 1/3 of the tank, so will only heat 1/3 of the water the boiler coil heats. If you don't need all that hot water, less electrical energy is used.
For me, electricity is about twice the price of oil per kWh (I'm on a cheap fixed rate at 11p). Combine this with the fact it heats 1/3-1/2 of the water and it's far more efficient mode of heat transfer (the boiler is 84% efficient compared to 100% at the immersion) plus no losses from the pipe runs from boiler to tank and I'm pretty sure the immersion is considerably cheaper.0 -
Smiley_Dan wrote: »I want to add another caveat to this one. It depends how much hot water you need.
Typically an immersion coil will be positioned in the top 1/3 of the tank, so will only heat 1/3 of the water the boiler coil heats. If you don't need all that hot water, less electrical energy is used.
For me, electricity is about twice the price of oil per kWh (I'm on a cheap fixed rate at 11p). Combine this with the fact it heats 1/3-1/2 of the water and it's far more efficient mode of heat transfer (the boiler is 84% efficient compared to 100% at the immersion) plus no losses from the pipe runs from boiler to tank and I'm pretty sure the immersion is considerably cheaper.
99% of cylinders are 36".
The bottom of a cylinder is always concave by around 3".
99% of top entry immersion heaters are 27", the immersion boss is usually about 3" down.
By my calculations this only leaves a 3" gap between the bottom of the immersion heater and the bottom of the cylinder. Almost the entire cylinder is heated.
Some cylinders did have 2 side entry immersion heaters at different heights, but these are very rare and usually used with economy 7 systems (no option to heat from gas boiler)On the internet you can be anything you want.It`s strange so many people choose to be rude and stupid.0 -
Oh yeah, should've added my cylinder is side entry. Ok, I edited my post to be clear this is more my case rather than the general case.
Is that really that rare? 99% rare?
p.s. I'd love a second, lower side entry coil... would be great for the solar PV diverter.0 -
99% of top entry immersion heaters are 27"
My 6 month old Stainless Steel cyclinder, made by Copperform, has a 21" as standard and the 27" 'option' has been discontinued.
Does anyone have a recommendation for one of those 'custom' immersion makers?4kWp, Panels: 16 Hyundai HIS250MG, Inverter: SMA Sunny Boy 4000TLLocation: Bedford, Roof: South East facing, 20 degree pitch20kWh Pylontech US5000 batteries, Lux AC inverter,Skoda Enyaq iV80, TADO Central Heating control0 -
Also, are you sure about this, given stratification? I see a lot of discussions around suggesting this isn't the case, e.g. http://www.navitron.org.uk/forum/index.php?topic=20931.0By my calculations this only leaves a 3" gap between the bottom of the immersion heater and the bottom of the cylinder. Almost the entire cylinder is heated.
Would be interesting to understand the physics behind this. I'd have thought you're always going to get more extreme stratification from a top mounted immersion because of its profile - being vertical it has little water above it compared to a horizontal mount.0 -
Smiley_Dan wrote: »Also, are you sure about this, given stratification? I see a lot of discussions around suggesting this isn't the case, e.g. http://www.navitron.org.uk/forum/index.php?topic=20931.0
Would be interesting to understand the physics behind this. I'd have thought you're always going to get more extreme stratification from a top mounted immersion because of its profile - being vertical it has little water above it compared to a horizontal mount.
As a plumber I've been changing cylinders for the last 30 years and can only speak from experience. When fully draining a cylinder down with a hose pipe and siphoning the water out ( with the hose at the bottom) its always hot right to the end.
There are two ways in which you pay for energy used for hot water. The first is to reheat the hot water that comes out of the tap and this cost is the same if you have a 10 litre tank or a 1000 litre tank.
The second is the heat loss from the tank when the hot water is stored, which is very little on a well insulated tank and the difference between a tank that half heated at the top and fully heated will be small.
No I cannot do the maths, but I can tell you that if you go feel your insulated cylinder at the sides you will see what I mean.
Also for at least 6 months of the year (usually 9), the heat loss from the cylinder isn`t a loss at all as it warms the house and reduces the load on the space heating. ( now some one is going to say that they have a cylinder in the attic).
The guy in the link that you posted strikes me as a bit of a fool. He goes out of his way to have a 33" immersion heater specially made. If there were a need for a 33" immersion heater surely there would be companies selling them.On the internet you can be anything you want.It`s strange so many people choose to be rude and stupid.0 -
Of course I bow to your experience, I am but a home handyman with an interest in green building, but...
Forgive my lack of understanding, but if the hose is at the bottom won't the water at the end be from the top, therefore that's as you would expect with stratification?When fully draining a cylinder down with a hose pipe and siphoning the water out ( with the hose at the bottom) its always hot right to the end.
In theory yes... the trouble is the quoted figures are not real world because they don't include conduction through pipework and the water in the pipes. Vented systems are especially bad for this I think (again, not sure on the physics, just my own experience of my own system).The second is the heat loss from the tank when the hot water is stored, which is very little on a well insulated tank and the difference between a tank that half heated at the top and fully heated will be small.
Also, in a system with hot water on top and cold water below, eventually the heat will conduct downwards, although this is a much slower process.
This is true, providing you want to heat that room at all times the cylinder is heated and you have theoretically perfect insulation in that room (clue: you don't).Also for at least 6 months of the year (usually 9), the heat loss from the cylinder isn`t a loss at all as it warms the house and reduces the load on the space heating. ( now some one is going to say that they have a cylinder in the attic).
Also - better make sure there are no gaps between pipework and wall/ceiling in that room... too many tradespeople leave enormous gaps without filling them. Leads to horrendous heat loss.
I actually don't like this line of thought at all. It's similar to "you don't need to lag pipes in heated space". You have no idea how spaces will be heated in the future, so why not just make sure the system you are installing works as best it can without trying to predict how other systems will work?
Sorry when I use "you" I don't mean YOU, I mean anyone. I don't mean to get at you, just the way I have been thinking about things recently. I am open to having my mind changed.0 -
The guy in the link that you posted strikes me as a bit of a fool. He goes out of his way to have a 33" immersion heater specially made. If there were a need for a 33" immersion heater surely there would be companies selling them.
Well, I'm trying to get a 30" one at the moment.
My current top mounted immersion is 21". The cylinder manufacturer tells me that the thermostat is only 5" long. I get only about enough hot water for a shower or a shallow bath, if we're lucky and the water is super-hot. This is only about 1/3 of a tank and is fully heated by about 11am on a sunny day. The supplier tells me that these are fitted to secondary cylinders (gas CH) and are intended for emergency use only.
I've spoken to the immersion manufacturer this morning and they can supply a 30" (the longest that will go in the tank) but the longest thermostat available is only 18".
I'm not sure what format this will be - some have a folded element at the bottom to get most heating effect as low down as possible.
I've tried using a de-stratification pump (which works brilliantly in terms of heating the whole cylinder, right down to the cold inlet), but having tried several pipe configurations, we can't stop it eventually filling with air, so I'm reluctantly giving up on that.4kWp, Panels: 16 Hyundai HIS250MG, Inverter: SMA Sunny Boy 4000TLLocation: Bedford, Roof: South East facing, 20 degree pitch20kWh Pylontech US5000 batteries, Lux AC inverter,Skoda Enyaq iV80, TADO Central Heating control0
, I must have clicked the link at the bottom of the wrong page. 
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