Hot water. Constantly on or on a timer?

[Mottie]

As above. I have always left our hot water on 24/7. Having it on a timer either once or twice a day would mean possibly heating it up from zero plus the fact that if two or three of you want a shower right after each other, the last one in could have a lukewarm one at best. Just to add, I have an unvented hot water cylinder and I’m assuming it’s well insulated as I get next to sod all heat off of it in the airing cupboard, all our airing cupboard heat comes from the associated pipe work.

What’s your opinion?

 

[xd400]

What are your electric bills like? They should significantly fall if you place it on a timer.

You're not heating from zero with a timer, the cylinder is lagged to keep it warm for a good deal of time.

 

[Mottie]

Sorry, forgot to say, it’s heated by the gas boiler. Gas bills are not too bad. Our combined gas/electric bills run at around £85 per month, averaged out over the year. 3 bed semi, 10 rads.

 

[dilalio]

Actually a good question and there will be a few different opinions I would think.
One option would be to set it to heat for DHW during non-demand periods for CH... that way you would be concentrating all boiler heat to the cylinder, thus improving recovery time for the stored DHW.

 

[Mottie]

Typical situation - I had a long, hot shower last night about 9.00. I literally stayed in the shower until it went cold. Had it been on a timer, that water would have remained cold until 20 minutes or so after the hot water had came on and if we had it set to come on the same time as the heating, we'd have had no hot water when we woke up this morning.

Also, sorry to sound thick but I’ve seen it a few times, what's DHW? (I’m guessing the HW is hot water, but what’s the D?)

 

[dilalio]

Domestic

 

[JohnD]

If you look at your gas bills during the summer, you will see what it costs you to heat the cylinder.

look at the usage charge, not the standing charge.

It will be a trivial amount.

Some people use about 25p a day for dhw, of which lost heat is a tiny proportion.

With a gas boiler and a cylinder, there is actually a saving in heating it fully once or twice a day, rather than a few pints every time you run a tap, because every time the boiler starts, you have to heat up all the metalwork and water in the boiler and the connecting pipes. Before and during the time people have baths and showers is a good time to do it. While people are wallowing in the bath, then towelling off, it will be reheated. A modern cylinder is usually quite big and well-insulated, so it will have plenty for handwashing and washing up during the day without needing to start the boiler again. People who live alone may need to run it less than an hour a day, so the boiler is also quieter as it hardly ever runs. The cylinder stat will turn off the boiler once the cylinder is fully hot and demand is met.

If you have a modern boiler it is likely to have more than enough power to heat the cylinder and all the radiators. Except when you come home to a cold house in frosty weather, the radiators don't need full blast from the boiler. Listen to your boiler in the morning, you will probably hear it firing up and running hard for ten minutes or so, then, once the radiators are warm, it will modulate down, and it will reduce still more as the rooms warm up and the TRVs start to close.

 

[Mottie]

Ok thanks. It isn’t a modern boiler - it’s a near 25 year old Potterton profile so I don’t think it modulates although we recently had a digital room stat and controller fitted and that seems to modulate the boiler somehow. When it gets to within a degree of the set temperature it switches off for a while, then restarts, then switches off until room temperature is reached. It then fires up for a few minutes probably half a dozen times per hour. I thought that was wrong but the thermostat supplier tells me that’s what us supposed to happen. It’s a Honeywell DT90e I think.

We have a 150 litre hot water tank. I suppose my next question would be, if on a timer, should it be set for once or twice a day? My wife normally has her shower/bath around 7.00 pm but I don’t normally have mine until 10.30-11.00 pm so perhaps set it to come on once at around 8.00pm after she's had hers and again after I’ve had mine at say, 5.00 in the morning. If I do that, assuming we only use a couple of sink fulls in the morning for washing/washing up, would it still be hot enough for her bath/shower that night?

Come to think of it, that’s roughly what happens now - it must heat up the water after she's had her shower and I know it comes on again after I’ve had mine as I can hear it working when I’m in bed and the heating is off. With very little usage, would the hot water come on again during the day due to heat loss? If it did, it would be minimal I suppose as it will only be topping up the water temperature a few degrees and not heating it up from a very low temperature.

Is it a bit like driving a car - do you keep a light throttle and cruise along at 60mph or do you drop down to 30, accelerate to 60, drop down to 20, accellerate to 60........ I’m sure the second method uses uses more fuel. That is my thinking behind leaving it constantly on along with the knowledge I’ll always have hot water at the times we'll be using it for bathing/showering.

 

[JohnD]

yes, I've had a Profile. It's a big iron boiler so it takes a fair amount of heat to warm up the iron, and then afterwards the heat just oozes out and warms the garden, and the ceiling of the room it's in.

You have a big cylinder, and once a day might be enough, but I'd set it to run for an hour in the morning, starting half an hour before you get up, and the same in the evening, starting half an hour before bathtime. it will not actually run for as long as that, because as soon as the cylinder is up to temp, it will stop calling for heat. A modern cylinder can nominally heat up in 20 minutes but I find in practice it takes longer.

Set the timer so it is off when you want to be asleep, because a Profile is a bit noisy, especially if the fan bearings are worn out.

Your modern cylinder will stay hot for a couple of days if you don't use the water. I don't actually know how long, but heat loss is very slow. I've had a hot bath after working in a house for a weekend when the power has been off since Friday. 210 litres will give about two baths or several showers.

Do you have a system filter on your boiler to catch sediment particles? An old Profile may have quite a lot of corrosion collected in the bottom. If you are a keen DIYer a chemical clean is very easy and cheap.

 

[ianmcd]

your boiler has a fixed rate gas valve, no matter what external controls you fit the boiler can not modualate

 

[Mottie]

I sort of understand that about the boiler itself not modulating but when we had the old analogue controls, if we set the room stat at 25, the boiler would keep going until it reached 25. Now, if we set it at 25 it will keep going until say, 24. Switch off. Wait a while, start up again. Switch off at 24.5, switch off etc etc until 25 is reached. I enquirer online and by phone with Honeywell and they said it’s supposed to do that. Switch off near to set temperature, let the heat dissipate from the rads, switch back on, get more heat and repeat this until 25 is reached. Then it kicks in every 20-15 minutes even when it’s at 25 to keep the temperature constant. Much more comfortable. On the old one, it would switch off at 25 then the room temp would drop to say, 22 before it fired up again but the room got hotter than 25 as the rads still pumped out heat. Honeywell claim their method is more efficient. It certainly seems more comfortable.

 

[dilalio]

Boiler modulation is control of flame size (like turning the rings on a hob up and down). Your boiler is not capable of automatically adjusting flame size - it is just on or off, which is less efficient and puts more stress on the associated components than on a modern modulating boiler.

 

[Mottie]

yes, I've had a Profile. It's a big iron boiler so it takes a fair amount of heat to warm up the iron, and then afterwards the heat just oozes out and warms the garden, and the ceiling of the room it's in.

You have a big cylinder, and once a day might be enough, but I'd set it to run for an hour in the morning, starting half an hour before you get up, and the same in the evening, starting half an hour before bathtime. it will not actually run for as long as that, because as soon as the cylinder is up to temp, it will stop calling for heat. A modern cylinder can nominally heat up in 20 minutes but I find in practice it takes longer.

Set the timer so it is off when you want to be asleep, because a Profile is a bit noisy, especially if the fan bearings are worn out.

Your modern cylinder will stay hot for a couple of days if you don't use the water. I don't actually know how long, but heat loss is very slow. I've had a hot bath after working in a house for a weekend when the power has been off since Friday. 210 litres will give about two baths or several showers.

Do you have a system filter on your boiler to catch sediment particles? An old Profile may have quite a lot of corrosion collected in the bottom. If you are a keen DIYer a chemical clean is very easy and cheap.

I’ve just edited my post after looking at the hot water tank. Sorry, it’s 150, not 210. We had the system converted in January from conventional to sealed plus an unvented cylinder with new digital controller, room stat and valves and a boiler service. They gave it the thumbs up. We had a chemical clean and power flush at the same time. The heating company that carried it out said I wouldn’t need a magnetic filter with that system until I had a new boiler. I can only hear it slightly because the boiler is fitted in the loft just above our bedroom. I wouldn’t say it was overly noisy - it’s more the pumped water I can hear going down to the hot water tank in the downstairs airing cupboard.

 

[ianmcd]

think of modulation as an accelerator in a car, when a modulating boiler ignites it is foot down , as the system heats up the then the gas valve eases off, , your boiler can not do this, I know what it is doing but it is not modulating, you are using the wrong term