Megaflo unvented hot water cylinder with Horstman 7 timer - cost effectiveness

lassfarfromhome

Can someone please help me work out understand how to set the timer on my megaflo to be most cost effective?  I live on my own so don't use much hot water and I think the plumber who installed the timer set it to come on for way too many hours over the day.  My question is, will I save money by reducing the hours it comes on?  Or, is does the Megaflo just not heat the water if it's already hot so therefore it wouldn't make much difference to reduce the hours it comes on?  Thanks for any help!

grumpy_codger

lassfarfromhome said:

My question is, will I save money by reducing the hours it comes on?  Or, is does the Megaflo just not heat the water if it's already hot so therefore it wouldn't make much difference to reduce the hours it comes on?  Thanks for any help!

The latter - if the HW tank is well insulated. The better it is insulated, the less difference timer settings make.

TheGreenFrog

It probably depends on when you have a shower/bath.  if first thing in the morning then try heating the megaflow for 90 minutes, starting 45 minutes before your bath.  The aim is to ensure your water is hot for your bath and that the megaflow then heats up after you have run your bath, providing hot water for the rest of the day (megaflow retains heat well).  If water not hot enough then try two hours, starting an hour before your bath.

Your timer probably has a one hour override, so if you find that, for example, you want another bath later in the day and that the water is not hot enough you can just heat the megaflow for an hour.  The megaflow will have a thermostat so your boiler will not run once the megaflow is up to the target temperature, but there is no point in having the boiler fire up everytime the megaflow hot water drops a couple of degrees (eg because you have run the hot water tap for a short time). 

Albermarle

How is the cylinder heated? Is it electric or is it linked to a gas boiler/central heating system?

lassfarfromhome

Albermarle said:

How is the cylinder heated? Is it electric or is it linked to a gas boiler/central heating system?

It's electric.  I don't have gas.

lassfarfromhome

TheGreenFrog said:

It probably depends on when you have a shower/bath.  if first thing in the morning then try heating the megaflow for 90 minutes, starting 45 minutes before your bath.  The aim is to ensure your water is hot for your bath and that the megaflow then heats up after you have run your bath, providing hot water for the rest of the day (megaflow retains heat well).  If water not hot enough then try two hours, starting an hour before your bath.

Your timer probably has a one hour override, so if you find that, for example, you want another bath later in the day and that the water is not hot enough you can just heat the megaflow for an hour.  The megaflow will have a thermostat so your boiler will not run once the megaflow is up to the target temperature, but there is no point in having the boiler fire up everytime the megaflow hot water drops a couple of degrees (eg because you have run the hot water tap for a short time). 

Thanks TheGreenFrog.  Sounds like maybe I need to experiment a bit.  I have a bath in the evening only so maybe I need to set it to come on for a bit before that and also maybe for an hour in the morning so I have hot water during the day?  The plumber set it to come on at these times which I think is overkill: 3am-7am, 9am-11am, 4pm-6pm

lassfarfromhome

grumpy_codger said:

lassfarfromhome said:

My question is, will I save money by reducing the hours it comes on?  Or, is does the Megaflo just not heat the water if it's already hot so therefore it wouldn't make much difference to reduce the hours it comes on?  Thanks for any help!

The latter - if the HW tank is well insulated. The better it is insulated, the less difference tamer settings make.

Thanks!  That's good to know.  It's a megaflo by Heatrae Sadia - quite old now, maybe 25 years old.  There's no additional insulation to what is integral to the megaflo

FreeBear

lassfarfromhome said:

Albermarle said:

How is the cylinder heated? Is it electric or is it linked to a gas boiler/central heating system?

It's electric.  I don't have gas.

Are you on an E7 (or similar) tariff ?

If so, setting the timer to use off-peak electricity will reduce your running costs. Also turn the thermostat down to a temperature you are comfortable with. If you have any concerns about legionella, set the thermostat to 50-55°C and you'll be fine - When I had a hot water tank, I had the thermostat set for 45-50°C and it only got heated up once or twice a week during the summer months.

Albermarle

lassfarfromhome said:

grumpy_codger said:

lassfarfromhome said:

My question is, will I save money by reducing the hours it comes on?  Or, is does the Megaflo just not heat the water if it's already hot so therefore it wouldn't make much difference to reduce the hours it comes on?  Thanks for any help!

The latter - if the HW tank is well insulated. The better it is insulated, the less difference tamer settings make.

Thanks!  That's good to know.  It's a megaflo by Heatrae Sadia - quite old now, maybe 25 years old.  There's no additional insulation to what is integral to the megaflo

The integral insulation is all that is needed. A new one would probably insulate a bit better, but the cost of replacement could not be justified by the small savings.

As said due to the good insulation on the tank, it will not make a huge difference if it is on a lot, or just for shorter periods. However electricity is more expensive than gas, so with an electric heater, there will be most likely some cost savings by not having it on so often. Maybe not a lot, but some.

If you did shorten the times it is on you may as well do it significantly.
For example in our house on weekdays, there will typically be two showers a day and one bath. Very little hot water used otherwise. 
I have the hot water ( gas boiler) on for 45 minutes in the morning and 20 mins in the afternoon, which is sufficient.
The showers are not very long though.
I put it on again for 20 mins if there is an extra shower.
This only works if we do the same every day as then the water in the tank never gets actually cold.
If you start from cold you need it on longer.

lassfarfromhome

Albermarle said:

lassfarfromhome said:

grumpy_codger said:

lassfarfromhome said:

My question is, will I save money by reducing the hours it comes on?  Or, is does the Megaflo just not heat the water if it's already hot so therefore it wouldn't make much difference to reduce the hours it comes on?  Thanks for any help!

The latter - if the HW tank is well insulated. The better it is insulated, the less difference tamer settings make.

Thanks!  That's good to know.  It's a megaflo by Heatrae Sadia - quite old now, maybe 25 years old.  There's no additional insulation to what is integral to the megaflo

The integral insulation is all that is needed. A new one would probably insulate a bit better, but the cost of replacement could not be justified by the small savings.

As said due to the good insulation on the tank, it will not make a huge difference if it is on a lot, or just for shorter periods. However electricity is more expensive than gas, so with an electric heater, there will be most likely some cost savings by not having it on so often. Maybe not a lot, but some.

If you did shorten the times it is on you may as well do it significantly.
For example in our house on weekdays, there will typically be two showers a day and one bath. Very little hot water used otherwise. 
I have the hot water ( gas boiler) on for 45 minutes in the morning and 20 mins in the afternoon, which is sufficient.
The showers are not very long though.
I put it on again for 20 mins if there is an extra shower.
This only works if we do the same every day as then the water in the tank never gets actually cold.
If you start from cold you need it on longer.

Thanks, this is really helpful.  I think I could cut down significantly and never run out of hot water

lassfarfromhome

FreeBear said:

lassfarfromhome said:

Albermarle said:

How is the cylinder heated? Is it electric or is it linked to a gas boiler/central heating system?

It's electric.  I don't have gas.

Are you on an E7 (or similar) tariff ?

If so, setting the timer to use off-peak electricity will reduce your running costs. Also turn the thermostat down to a temperature you are comfortable with. If you have any concerns about legionella, set the thermostat to 50-55°C and you'll be fine - When I had a hot water tank, I had the thermostat set for 45-50°C and it only got heated up once or twice a week during the summer months.

No, I'm not on E7 but that's a good reminder to work out whether that might be cheaper, thanks!