hot water cyl lagging

[DrFfybes]

We have an old, 1980s(ish) hot water cyl lagged with a foam sprayed on to it. It is about 30mm thick. A couple of showers or a bath emptied the cyl, and after 24 hours away the water was pretty much cold, compared to the previous house with a well insulated megaflo which could keep it warm for 3 days.

We changed our boiler in May. With the old boiler, we had the hot water coming on twice a day for 30 min in summer (7am and 4pm), and 3 x 30 min in winter.

Whilst tidying the airing cupboard a couple of weeks after the boiler was done, I decided to invest in a tank jacket - https://www.screwfix.com/p/hot-water-cy ... 19mm/43483

Then got the IR thermometer out.... the surface of the tank was about 25C, so up to 5 degrees above ambient

The first thing I noticed was the old tank stat was buggered, the hot water was set to 60, but was barely reaching 50C. This was changed, and the tank jacket fitted. The cylinder surface inside the jacket is 40C today, 15C warmer than ambient. The jacket outside is at room temp.

Now that the cyl was getting hotter (and actually to a safe temp) and retaining the heat, we found we still had very hot water at lunchtime for washing up. We've gradually reduced the boiler timings from 2 x 30 min to 2 x 20 min.

Gas use has dropped, although it is hard to quantify the causes. The old boiler had a pilot light, so that has been saved. However we are now heating the water to a higher temp, which will increase gas use. I'm assuming hob use has remained constant. I did however take a lot of readings.

In the 2 weeks from new boiler install to tank stat change, lagging and changing the timings, gas use was down from last year's 1.5u/day to about 1.1u, which I will put down to the pilot light. 1u is about 11.2kWh.

With the jacket and the higher temp it used 28u in 30 days, and in the last 25 days with reduced timings to 2 x 20 min it is 0.68u/day.

I'll give it a week and see if we can get away with one heat cycle/day, and see what that does to the comsumption.

The tank temp varies, the top where it is drawn off can still be hot enough for use, but the the stat and heating coilare at the bottom, so the boiler comes on for a bit even if the top is still hot. I gather heating the tank from 30C to 60C once uses less gas than from 45 to 60C twice, due to lower return temps activating the condensing function.

However, ignoring the pilot light, it looks like the tank jacket, hotter water, and subsequent reduction of water heating time are saving approx 0.4U/day, say 5kWh, which on the current cap of 7.4p/kWh is 35p/day, which means the tank jacket pays for itself in about a month.

Paul (waiting for someone to spot the obvious flaw I've missed).

[JohnB]

I wrap a sleeping bag round mine. Might add another one this winter

[monabri]

I wrap a sleeping bag round mine. Might add another one this winter

Might be an idea to get in it with electric prices going through the roof!

[PhaseThree]

Paul (waiting for someone to spot the obvious flaw I've missed).

The only obvious flaw in the calculation is that the additional energy you were using was heating your house. Not ideal or necessary in the summer but you will probably notice come the winter. You have effectively removed a couple of heat sources that will need to replaced (all things being equal), probably by turning up the radiators by a notch in the surrounding areas.
Come the winter this may all be swings and roundabouts.

[BullDog]

I don't know how old the original boiler was. Quite old if it had a pilot light. On a sample of three in our family, three boilers were changed from rather old Baxi's to 2x new Baxi and 1x new Vaillant. In all three cases without any other change gas use dropped around 30%.

[DrFfybes]

I don't know how old the original boiler was. Quite old if it had a pilot light. On a sample of three in our family, three boilers were changed from rather old Baxi's to 2x new Baxi and 1x new Vaillant. In all three cases without any other change gas use dropped around 30%.

Glow-worm hideaway100, probably mid/late 1980s.

he only obvious flaw in the calculation is that the additional energy you were using was heating your house.

The old boiler did heat the kitchen a bit, however the HWC is in a cupboard off the landing which used to be roof void. It has a brick chimney on the left, outside brick wall to the right, and a sloping roof with no insulation, just the timbers and sarking felt then tiles. It got very cold in there in winter!

Paul

[xeny]

Reading the screwfix description, is it genuinely 80mm thick? If so I might trouble to replace the existing jacket on my hot water cylinder, which must be 25 plus years old, and is perhaps an inch thick at this point.

Keep in mind that as the weather turns you may need to extend the utterly optimised timings you're using at present - I add 5 minutes for winter and subtract 5 minutes for summer from my intermediate spring/autumn settings.

[DrFfybes]

Reading the screwfix description, is it genuinely 80mm thick? If so I might trouble to replace the existing jacket on my hot water cylinder, which must be 25 plus years old, and is perhaps an inch thick at this point..

Probably - it comes vacuum packed and you unroll it and it self expands. I just shoved a tape between the panels and it was between 75 and 110mm from the tank to the outside of the jacket Also still quite warm in there despite a day of use since the last heat cycle.

Keep in mind that as the weather turns you may need to extend the utterly optimised timings you're using at present - I add 5 minutes for winter and subtract 5 minutes for summer from my intermediate spring/autumn settings.

Probably more than that - the cold is fed from a loft tank for both the cyl and the shower, which will be a lot colder in winter so the shower will use more hot to compensate for the colder cold coming into the mixer. Also the incoming water to the tank will be colder, and the ambient temp around the cyl will be a lot lower so more heat loss there.

Last year we used 28,000 kWh of gas, so it will be interesting to see how much more efficient the boiler is. That was with a room stat at 15C and only heating the rooms we use - microbore pipes means getting all the rads warm takes over an hour.

Paul

[scotview]

We have an old, 1980s(ish) hot water cyl lagged with a foam sprayed on to it.

We similarly have a sprayed foam copper cylinder. Having got a good handle on what our boiler/central heating system was doing, I wished to find out what the cylinder was doing (bit of a nerd).

I got a cheapo temperature/humidity monitor with a probe and put on the cylinder. The graph attached, from CSV file, shows the temperature trend. The first bit I think the probe was not in adequate contact with the cylinder. I pushed it further into the foam jacket at a factory cut out about a quarter down. You can see the consistent temperature range and the cylinder decay rate which looks not too bad.

The temperature in the cold feed tank in summer gets almost "pre-heated" in the loft. The winter might be poorer with cold loft temperature.

I need to check that the cylinder is going to 60C. You get smart stats now which will go to 60C once a week, might get one of those and drop the tank temperature.

One question, would the stainless temp probe induce corrosion where it touches the copper tank, the atmosphere is obviously very dry.

[DrFfybes]

I need to check that the cylinder is going to 60C. You get smart stats now which will go to 60C once a week, might get one of those and drop the tank temperature.

I wondered about that - we're getting a partial rewire and I thought about a seperate feed for the immersion (currently off the ring main) and setting the boiler fed stat back to 53C and heating twice a day, with a weekly boost to 60C off the immersion.

One question, would the stainless temp probe induce corrosion where it touches the copper tank, the atmosphere is obviously very dry.

Copper and stainless (depending upon quality) are quite close on the Galvanic corrosion scale. However a physical barrier such as a coat of nail varnish or simply a bit of insulating tape (which doesn't insulate as far as heat is concerned!) between yhem would stop it.

Paul

[Mike4]

We have an old, 1980s(ish) hot water cyl lagged with a foam sprayed on to it. It is about 30mm thick. A couple of showers or a bath emptied the cyl, and after 24 hours away the water was pretty much cold, compared to the previous house with a well insulated megaflo which could keep it warm for 3 days.

This is interesting. I've heard that the yellow spray foam insulation loses its effectiveness as insulation as it grows older, which your story rather supports.

I remember the first time I ever fitted one of these newfangled foam insulated cylinders. Must have been back in the late 70s. I'd fitted a whole new central heating system and I fired the boiler for half an hour late on a Friday afternoon before going home for a long weekend. When I returned to the (empty) house on Tuesday I was utterly phased to find the hot water cylinder full of piping hot water despite me having turned the gas and leccy OFF on the Friday night and the house being empty in the interim.

The half hour test run on Friday had clearly heated the cylinder which then stayed hot all the way through until Tuesday, whereas your 40 year old spray-foamed cylinder loses its heat in 24 hours. I have to put this down to age degradation of the spray-foam insulation.

[DrFfybes]

The half hour test run on Friday had clearly heated the cylinder which then stayed hot all the way through until Tuesday, whereas your 40 year old spray-foamed cylinder loses its heat in 24 hours. I have to put this down to age degradation of the spray-foam insulation.

Yebbutt, How?

Surely the purpose of the foam is to trap the air next to the cylinder, which it should still do.

I may have exaggerated the decay slightly, as I don't think we turn it off for 1 night away, but certainly going away Friday meant returning Sunday to tepid water (although as I since discovered it was only heating to circa 50C).

Oh, yes..

I wrap a sleeping bag round mine. Might add another one this winter

I considered a quilt or sleeping bag, but the custom jacket looked a lot less work and is certainly cheaper than a similar thickness bag, though ASDA do very cheap double quilts.

Paul

[scotview]

I have to put this down to age degradation of the spray-foam insulation.

Interesting about the foam degredation.

Here's another one for you Mike.

I switched off the cylinder heating from the boiler and switched on the electrical immersion heater to see if it would push the cylinder temperature up to 60 deg.

The cylinder temperature just kept falling, I think the emersion is faulty.

But one question please, what is the usual high to low switching range for a cylinder stat or an emersion heater ?

The cylinder temperature went low as 45 deg C and didn't rise, so presume the emersion is broke.

Ta

[BullDog]

I have to put this down to age degradation of the spray-foam insulation.

Interesting about the foam degredation.

Here's another one for you Mike.

I switched off the cylinder heating from the boiler and switched on the electrical immersion heater to see if it would push the cylinder temperature up to 60 deg.

The cylinder temperature just kept falling, I think the emersion is faulty.

But one question please, what is the usual high to low switching range for a cylinder stat or an emersion heater ?

The cylinder temperature went low as 45 deg C and didn't rise, so presume the emersion is broke.

Ta

Easiest way to check is to turn the immersion heater off. Ask someone to turn it on while you watch the electricity meter. When it's switched on, you'll immediately see a jump in consumption from the immersion heater. From memory they're around a 3kw load so the meter will react immediately if the heater is drawing current when you switch it on.

[xeny]

The half hour test run on Friday had clearly heated the cylinder which then stayed hot all the way through until Tuesday, whereas your 40 year old spray-foamed cylinder loses its heat in 24 hours. I have to put this down to age degradation of the spray-foam insulation.

I suspect the well ventilated nature of the good Dr's airing cupboard may also be a factor.

[DrFfybes]

The half hour test run on Friday had clearly heated the cylinder which then stayed hot all the way through until Tuesday, whereas your 40 year old spray-foamed cylinder loses its heat in 24 hours. I have to put this down to age degradation of the spray-foam insulation.

I suspect the well ventilated nature of the good Dr's airing cupboard may also be a factor.

Yes, the only time we've been away for more than 1 night since we moved was over Xmas.

Keep in mind that as the weather turns you may need to extend the utterly optimised timings you're using at present - I add 5 minutes for winter and subtract 5 minutes for summer from my intermediate spring/autumn settings

As it happens we overoptimised - 20 min in the morning isn't quite enough if we donn't shower until evening.

Paul (currently waiting for the immersion to top the tank up)