Best settings for efficient hot water heating?

BeeTheGoddess

Hi there, I'd be very grateful for any advice on the best programming for hot water heating please. We have a condensing boiler which we use for both heating, and the hot water tank (no working immersion heater at the moment). The tank has a thermostat. Detailed breakdown of our system in this thread, if any additional info matters: https://forums.moneysavingexpert.com/discussion/6527766/help-diagnosing-hopefully-fixing-a-hot-water-supply-issue/p1

Currently, the programmer is set for the hot water to be on 6:30-8:30am, briefly at 12pm, then 5pm-10:30pm. Our hot water use (2 person household) is showers in the morning before work, then one of us prefers to shower straight after work and the other has a bath later in the evening just before bed. And one or two rounds of washing up during the day. 

I vaguely feel like we don't need it to be on as much, especially in the evening, but don't want to accidentally reduce it to a point where there's not enough for a hot bath that I've been looking forward to all day! I'm also not sure how much changing the schedule would produce reduced costs, given that (presumably?) the thermostat stops it heating more than it needs to. 

Would be very grateful for any advice on what a more suitable schedule would be, which might save some money. 

tim_p

Start by simply cutting back those hours. You’ll soon learn what does or doesn’t work. It won’t be running constantly during those hours (or shouldn’t!). Also look at times when hot water is used.   If you skip the brief 12.00pm slot do you notice any effect? 

Experiment basically. If it’s your only use of gas at this time of year then take some regular meter readings to see what happens to actual usage. 

vacheron

We have a thermal store which is broadly the same as a hot water tank, but it is refilled automatically whenever the central heating is on, so we never need to use the hot water directly in winter. 

In the summer we find that a 30 minute blast is sufficient to give our family of 3 enough hot water for general washing, dishes and basins for at least a day, sometimes 2. However as I use a Hive thermostat via my smartphone I can just press one button to give the hot water another 30 minute boost if I feel it starting to run cool. 

If course, the size of the tank and water temperature would greatly affect the amount of water available on a house by house basis. 

If however there are multiple showers or baths planned, I set it to run about 10 minutes beforehand and switch it of once everyone is showered or the bath is filled.

8+ hours a day seems like a lot ot me, but of course if your tank thermostat is set correctly, this will switch the boilder off once the tank reaches temperature anyway. And you may not prefer to control your hot water "Ad-Hoc" the way I do! 

FreeBear

BeeTheGoddess said:

Hi there, I'd be very grateful for any advice on the best programming for hot water heating please. We have a condensing boiler which we use for both heating, and the hot water tank (no working immersion heater at the moment). The tank has a thermostat. Detailed breakdown of our system in this thread, if any additional info matters: https://forums.moneysavingexpert.com/discussion/6527766/help-diagnosing-hopefully-fixing-a-hot-water-supply-issue/p1

Currently, the programmer is set for the hot water to be on 6:30-8:30am, briefly at 12pm, then 5pm-10:30pm. Our hot water use (2 person household) is showers in the morning before work, then one of us prefers to shower straight after work and the other has a bath later in the evening just before bed. And one or two rounds of washing up during the day. 

I vaguely feel like we don't need it to be on as much, especially in the evening, but don't want to accidentally reduce it to a point where there's not enough for a hot bath that I've been looking forward to all day! I'm also not sure how much changing the schedule would produce reduced costs, given that (presumably?) the thermostat stops it heating more than it needs to. 

Would be very grateful for any advice on what a more suitable schedule would be, which might save some money. 

Even although the timer says hot water at 06:30-08:30, top up at noon, and then on again in the evening, it doesn't mean that the boiler will be running all the time during those time slots. The thermostat controls when the boiler fires up. You have a relatively new water cylinder with a reasonable level of insulation. So the heat loss is not going to be huge. Even so, tweaking the settings will reduce gas consumption a little.

What I would do is dial the thermostat back to 50-55°C, and set the timer for 30 mins to an hour before you get up. That will give you hot water for the morning showers. Cut out the call for hot water at noon, and split the evening slot in to 17:00-18:00 and 21:00-22:00.

Even with a condensing boiler, it is not running very efficiently when heating hot water (probably around 86%). At start up, efficiency is even lower, so the fewer times the boiler runs, the better.

Rodders53

The HW tank looks to be an vented CW in loft fed system from the picture in that other thread.  Imho, a relatively old vented HW tank to boot. {Possibly made in week 34 of 1995 from the scrawl on the insulation?}  Also relatively small capacity. Probably 140 litres (1050x450 mm ) or even less if the tank dimensions are smaller.

But that doesn't necessarily affect the operation of it for the use indicated, except a bath may pretty much exhaust the HW supply?

IF it's a thermal store the OP needs to clarify things for us all as it may then need a different approach.

Trial and error is the key.  The cylinder is likely to reheat from 'empty' in around 30 minutes on gas (longer via an immersion).  I'd consider lagging the pipes and adding a jacket to retain heat in the cylinder more if I were the OP.

bob2302

IMO the most  important thing is to minimise the amount of hot water in the tank overnight and during the working day, so make sure it's off before the first use of the day and by the time you take a bath.

Reed_Richards

If you had a perfectly insulated hot water tank then it wouldn't matter when you heat it.  But it won't be perfectly insulated, it will lose heat and the hotter it is the more heat it will lose.  So the secret is to keep it as hot as you need it and no hotter and to only bring it up to temperature shortly before you are going to use hot water.

Ectophile

My boiler will re-heat a tank in about 40 minutes if I haven't run it stone cold.  If it is stone cold, then it gets the water to an acceptable temperature in that time.  But a bath will use much of the hot water in the tank, and what's left will only be warm.

I think you could get away with a few bursts of 40 - 60 minutes throughout the day, timed to come on after you have used the hot water.

Maybe my boiler thermostat and tank thermostat aren't set right, but I find my boiler keeps running for the whole 40 minutes, even if it is only working on the lowest power.  So I wouldn't want to extend the period.

I would recommend getting the immersion heater fixed, for emergencies.  You never know when the boiler will go wrong.  While using electricity to heat the tank is expensive, it's still cheaper than calling out an emergency plumber.

RavingMad

What saves money for us is turning the water temperature down on our cylinder to 45⁰. Our family of 4 only really uses hot water for showers/baths as we have a dishwasher.

We all turn down the temperature during showers and baths so the water is plenty hot for us

Two 30 min sessions uses about 5kwh a day during the summer 

vacheron

RavingMad said:

What saves money for us is turning the water temperature down on our cylinder to 45⁰. Our family of 4 only really uses hot water for showers/baths as we have a dishwasher.

We all turn down the temperature during showers and baths so the water is plenty hot for us

Two 30 min sessions uses about 5kwh a day during the summer 

The only thing to be careful with here (as you mentioned Cylinder) is that 45C is very close to the optimum growth temperature for legionella which is why the general rule is to keep cylinders at at least 55-60C.

If there is a lot of regular hot water use (and therefore turnover of water in the cylinder) this shouldn't cause a problem in a domestic setting, just something to be aware of.

FreeBear

vacheron said:

RavingMad said:

What saves money for us is turning the water temperature down on our cylinder to 45⁰. Our family of 4 only really uses hot water for showers/baths as we have a dishwasher.

We all turn down the temperature during showers and baths so the water is plenty hot for us

Two 30 min sessions uses about 5kwh a day during the summer 

The only thing to be careful with here (as you mentioned Cylinder) is that 45C is very close to the optimum growth temperature for legionella which is why the general rule is to keep cylinders at at least 55-60C.

The risk of legionella is extremely low with just some 400 cases reported annually (half of which are contracted overseas). With an unvented DHW tank, the only path for infection is from the main water supply which has been treated to kill pathogens. In a vented system, the bacteria could be introduced in to an uncovered header tank by birds or possibly bats. For the vast majority of people, this is not a risk. In the unfortunate event of legionella contaminating the water, the main path of infection is through inhalation of water droplets.

Humidifiers and hot tubs are the biggest risks in a domestic environment (in commercial premises, one can add water cooling towers).

I used to run my DHW system (vented with a covered header tank in the loft) at ~45°C, and now using a combi boiler at 42-45°C. During the summer, gas consumption is around 2.5-3kWh for hot water, and virtually zero risk of legionella.