How best to use /set hot water system..

Depends how well your tank is insulated. There's only one way to find out, really.

so how long SHOULD:
a - it take to properly heat the water in a tank
b - said water remain hot

Ta

DrP

We have ours set to heat for an hour from 6.30am and again at 4pm. Works for us.

Maybe the kids will learn to shower when the water is hot? Maybe I'm a bad dad.

It all depends on how good your tank insulation is. Ours stays warm for ages if no-one uses it. However it does contain enough water for three pretty long showers.

Also depending on how much noise it makes. If it's not going to wake anyone up, you could consider just leaving it on all the time. Of course it won't be running all the time, only when the temperature in the tank drops, which will be when someone's used it - but it might come on in the middle of the night.

However I'd probably set it on a couple of hours in the morning and in the afternoon say 4pm. It'll stay warm between those times, as long as no-one empties it. If this isn't enough go for an hour from 6am or whatever, then all evening.

a - It takes about 45 mins to fully heat from stone cold? I dunno really.

b - ours remains hot enough for a shower for ooh, 36 hours, but it gets cooler from the bottom of course. So there might be enough for just one shower after that time. At various times our hot water packed up we didn't notice for a day or two.

Depends how well your tank is insulated. There’s only one way to find out, really.

This - ours was installed about 8 years ago and is so well insulated we don't need to consider how long the water will stay hot for (it'll easily stay hot enough for 48+ hours).

a – it take to properly heat the water in a tank

That depends on (at least) two factors; how efficient the boiler is and how big the water tank is.

so how long SHOULD:
a – it take to properly heat the water in a tank
b – said water remain hot

I'm not a heating engineer - but applying some science (with some example data) suggests to me...

Tank = 200 L
Temp In = 10 deg C
Final Temp = 60 deg C
Boiler Power = 30 kW

Energy = 200 KG x 50 deg x 4 KJ / kgDeg = 40,000 KJ = 11 kWh

Time = 11 kWh / 30 kW = 20 minutes to heat a full tank of cold water.

Tank Heat Loss = 1.4 kWh / day according to https://cdn.plumbnation.co.uk/site/heatrae-sadia-megaflo-eco-250i-indirect-unvented-hot-water-cylinder/heatrae-sadia-megaflo-technical-sheet.pdf. You might have a less well insulated cylinder.

The heat loss will decrease as the tank cools - this assumes you're keeping it at 60 degrees. If you heat it once a day then it would need 1.4 kWh adding back - so 2 minutes from a 30 kW boiler. It would be around 6 degrees cooler (50 degrees x 1.4 kWh / 11 kWh).

You could reduce energy required by a theoretical max of 1.4 kWh per day by reducing the average temperature of the tank by not heating it after the hot water is used, then heating it as close as possible to when the water is needed. Since you can't do this because of irregular use times you might as well just leave the hot water permanently on.

An hour in the morning & late afternoon sounds like a sensible start point, then adjust as required with experience.

How old are the kids? Presumably old enough to be able to hit the override button (or the +1hr button if there is one) if they use a lot of water at an unusual time.

With a tank, you can never guarantee hot water if people are using it at odd times, but for most of the time you can get it right. And a couple of occasions of "DAD, THERE'S NO HOT WATER......" will probably remind them that they need to stick the override on....?

Family of 5 here (2 teenage boys and 10 year old girl) in a modern (4 year old) house and I put water on for 1 hour at 6am and another hour late afternoon. If everyone has showers I just whack it on for an extra hour.

I’ve quickly set it to heat the tank for an hour in teh am, and an hour in the late pm…
Will this keep the tank hot for long enough?

No.

All morning and from after school to 9 at night. The thermostat will regulate it and as long as it's really well insulated you won't lose much heat at all. An hour is nowhere near long enough for the vague washing timescales of kids.

I presume the bathroom radiator is on a bathroom circuit too, the tank cycling heats the towel rail and gives you a fighting chance of keeping the kids in dry-ish towels.

if a decent tank really loses 1.4kwh per day (which isn't "lost" really, it just goes into the rest of the house - so if you're paying for heating anyway you just pay slightly less for heating) then it would only cost you about 5p/day to keep it hot the whole time, compared to maybe 3p/day to have it on some of the time.

Just leave it on 24/7

if a decent tank really loses 1.4kwh per day (which isn’t “lost” really, it just goes into the rest of the house

Well that depends on the situation. Our HW tank is at the top of the stairs, where the bedrooms are with closed doors. The landing is lovely and warm which is great if you want to spend time on the landing in winter. In summer it's really bad as my daughter's room gets absolutely roasting.

We've helped that by lagging all the pipes in the cupboard, and stuffing duvets and pillows all around the tank. And turning the temperature way down.

Temp In = 10 deg C
Final Temp = 60 deg C

Oof, those are extremes. Cold water is nowhere near that cold, and 60C is I think dangerously hot water no? The hotter you heat it the more you lose because the differential is greater. I think ours is maybe 45C?

Just leave it on 24/7

As long as it doesn't wake anyone up. Ours would.

Cold water is nowhere near that cold

Depends where you live 😉

And turning the temperature way down

I think ours is maybe 45C?

you should have it at 60 to avoid legionella bacteria. Why a tanked system can't be set to blast up to 60 at, say, 1am (to kill the bugs) then cool down a bit by the time you actually use it, I don't know. 45 is extra-dangerous as its the temperature range that the bacteria actively multiply

The advantage of running it hotter is your bath fills quicker and showers have a bit more pressure (as you're able to mix more cold into them)

Just incase it's relevant, I used to live in a flat with solar panels that gave excess power to heat the hot water tank. I found it best to give it a quick boost post morning shower to get the newly replaced water up closer to temperature, then the solar panels could do the rest through the day. Conversely if I boosted pre shower then it needed much longer to get to temperature and I became totally reliant on the boost as the solar panels couldn't give enough juice through the previous day.

I posted this in "The Solar Thread" on the forum. so I'll copy it here too:

After fitting Solar Thermal (see entries in The Solar Thread) I’ve been keeping an eye on my smart meter and couldn’t figure out what was using 11kWh of gas a day. The meter reported this usage despite the sunny weather, no cooking and the Solar Thermal system heating the water up to 65+ degrees. What the hell is using it?

The pilot lights (I have two – one for a hot water boiler and one for heating).

I checked the smart meter half-hourly readings and sure enough, every half an hour day in, day out, 365 days a year I use 0.022m3 of gas. Over 24hrs that’s 1.056m3 (or 11 kWh). Over a year it’s 385m3 or 4066kWh!

That’s 27% of our gas usage.

Blimey.

They are both off now during this sunny spell, but I’ve lived with the system running like this for 22 years. That hurts my brain as I thought I was pretty efficient with our use of the system. I would always have put this level of daily use down to heating water previously…….

that sounds broken. 11kwh a day is approx 230w per pilot light. Thats a huge amount of heat being generated - hold your hand near a single old-school 100w bulb to see.

that sounds broken. 11kwh a day is approx 230w per pilot light. Thats a huge amount of heat being generated – hold your hand near a single old-school 100w bulb to see

Oh believe me I know! Since I've switched the pilot lights off on sunny days when we don't cook or heat water the usage remains at zero so I don't think the meter is faulty.

There'll be an adjustment on both gas valves somewhere that's potentially out of whack, but turning one off halved the amount used, so both pilot lights use the same amount of gas each. It's been serviced annually for the past 22 years it's never been flagged as an issue by the engineer, I just wish I'd spotted it sooner.

showers have a bit more pressure (as you’re able to mix more cold into them)

Not if your system is mains fed.

I'll look into the legionella thing tho ta.

Re pilot lights - what kind of antiquated system still has those?

I have mine set for an hour in the morning and an hour in the evening. Also for an hour between 13:00 and 14:00 but you won't need to do this if you don't have a postman and a binman lodging with you 🙂

All morning and from after school to 9 at night. The thermostat will regulate it and as long as it’s really well insulated you won’t lose much heat at all. An hour is nowhere near long enough for the vague washing timescales of kids.

I presume the bathroom radiator is on a bathroom circuit too, the tank cycling heats the towel rail and gives you a fighting chance of keeping the kids in dry-ish towels.

Ok, cheers.. seems the evil stepdad is being a bit tight...
And yeah...towel rail is on the same loop...

DrP

Re pilot lights – what kind of antiquated system still has those?

Indeed. In my case a Johnson and Starley warm air heater twinned with a water heater. It's actually a very quick system to warm the house and I think that given the speed of warm-up and the temperature regulation once the house is up to temp I believe it's way more efficient than boilers of a similar age. It probably has another 10-15 years of useful life left in it.

I'm currently investigating how I might replace the gas valves for self-igniting/non-pilot light ones but it looks like that'll cost a fair chunk. At least I'm aware of the issue now.

Not if your system is mains fed.

it can still make a difference - shower pressure is a result of both flow rate and pressure - increasing the flow rate (which is what having hotter hot water effectively does, by bringing more cold to the mix) will increase the pressure if the surface area of the shower head (as in, the holes in it) is larger than the amount of water you're able to push through the system right now.

simple way to test is to drop the temperature in your shower, if the pressure increases then increasing the hot water temp will increase the bau pressure.