PigletJohn - a plumbing question for you

[OurHouseAtTheEndOfOurStreet]

Any thoughts on this. If you have a megaflow - is it more economical to keep hot water on all day or to heat it for several hours in the morning and evening when people need showers like you would traditionally do with hot water?

there is a slight advantage in running the boiler fewer times per day.

The cylinder probably takes in the region of half an hour to heat from cold to hot. So set the timer to heat it from half an hour before people want showers, and to be on during the showers and for half an hour after they have finished. Then set the timer to off. That way, when you are running small amounts of hot water to wash up your mug or your hands or feet, the boiler will not start running for a few minutes to top up the few litres of water you have used. The cylinder will not run out of hot water during multiple showers if the boiler timer is "on" because the boiler will heat water almost as fast as you can use it. Add on dressing/undressing time, cutting toenails and brushing teeth, and it will be fully hot ready for the next person. Very few people run a drencher shower for long enough to use all the hot water in a Megaflo.

The cylinder will have more than enough hot water for your incidental usages between the morning and the evening rushes.

The saving is not heat lost from the cylinder, which is well insulated, but on heating up the boiler, and its pipes, and the water in the pipes between the boiler and the cylinder. This will all be wasted each time the boiler runs, so it is more economical to run it to fully heat the cylinder than to run it multiple short times.

If you set the timer for an hour morning and evening, before your heavy use of baths and showers, the boiler will be able to run for an extended period, but will turn off once the cylinder thermostat signals that it has reached the preset temperature.

Thanks Piglet John. Sorry I am being a bit dim here but are you saying don't' leave it on all day.

You say:
The saving is not heat lost from the cylinder, which is well insulated, but on heating up the boiler, and its pipes, and the water in the pipes between the boiler and the cylinder. This will all be wasted each time the boiler runs, so it is more economical to run it to fully heat the cylinder than to run it multiple short times.

Which sounds like it is better to leave it on all day

But you say

If you set the timer for an hour morning and evening, before your heavy use of baths and showers, the boiler will be able to run for an extended period, but will turn off once the cylinder thermostat signals that it has reached the preset temperature.

Which sounds like I should just run it twice a day?

So simply put, which is the more economical way to set the hot water to run A or B?

A) 5.30am - 8.00am and 6.30pm to 10pm
B) 5.30am - 10pm

Thanks

There should be a question mark at the end of that first sentence!

I don't know if it helps, but the way I read PJ's advice is that A is the answer. However, you possibly have the timer set for too long unless the first shower is at 6am and the last at 7.30am and in the evening it may not even be necessary if there aren't showers and baths being taken.

@PigletJohn sorry to hijack this thread but I've had to plumb my dishwasher onto the hot tap as the washing machine is on the cold one.
Is this going to hike my gas bill ?

Sorry OP !

twofloors I can answer that one - you might up your gas bill slightly but in theory you should save on your electricity bill, e.g. a Miele dishwasher on a 60 degree C hot fill connection will use 50% less electricity (and run time will be slightly shortened too).

However, as dishwashers don't use much water it depends on the length of run of pipe feeding the dishwasher and whether you are taking hot water from a combi boiler or a cylinder - the dishwasher may have filled before the boiler kicks in or before hot water from the tank reaches it. If it is plumbed in close to a sink then run the hot tap just before switching it in may help.

Just get the pipework adjusted with a spur for the dishwasher.

A) 5.30am - 8.00am and 6.30pm to 10pm

is cheaper.

The cylinder will stay hot all day because it is well-insulated. Until you run enough baths and showers to use it all up.

twofloorsup

if you have a combi boiler, then it will be more economical to use cold fill.

If you have a cylinder it's hard to say, it will depend on pipe runs, and any saving will be small because of the small amount of water used.

You can get a Y-shaped adaptor for the appliance tap, but they are a bit of a bodge and I would not trust them not to leak or come apart. It is an easy job for a plumber or a competent DIYer to fit an additional appliance tap.

Thanks all for your help. I had a Y pipe on there but like you say it was unreliable and kinked so the washing machine wasn't working properly.
I do indeed have a combi boiler but am reluctant to do any plumbing work as I rent the property and don't feel it's a secure tenancy.
Thanks again.

Thanks Piglet John!

Hey PigletJohn I've got one for you as well...
I am converting part of my house into a separate dwelling. It's small - one bed, and I just need to heat hot water for a shower and kitchen use. I'm not going to put gas in, so want to go for electric heating and water. What kind of thing do I need install to provide sufficient hot water? It will need to go downstairs, shower is upstairs, mains supply - if these details are relevant.
Thank you for all the advice you give on this board!

the person living in it will be very reluctant to pay the fuel bills, since electricity costs about four times as much as gas.

Run the kitchen cold tap into a bucket, and time it to full.

it needs at least 12 litres per minute to provide a tolerable shower. If it is a conversion, and shares a supply pipe with the rest of the house, the pressure and flow may be inadequate. A dedicated supply pipe out to the road might be needed.

If the supply is poor, you may need a loft tank and a shower pump.

It will have a news mains supply. There is no loft - the bedroom is built into the loft. The person living in it will be me. The clue is in my name - husband died, left me in a bad place, I am trying to salvage some kind of home for myself (sad story). So I really need to figure out the best possible way to do this. I could get gas put in, but a new gas supply will also be very expensive.

if you're putting in a new waterpipe, do it in 25mm with full-bore valves and connectors, all the way to an unvented cylinder. This will give you good flow and a satisfying shower. If you had two bathrooms I'd say 32mm.

You can get a cylinder with an upper and a lower immersion heater. The upper one will heat small quantities quickly, the lower one will heat large quantities slowly. A 3kW immersion heater warms roughly 1 litre per minute.

If you ever get Economy 7 or Solar you can heat the whole cylinder from the bottom element at reducedcost. Megaflo is a brand name, there are others. They are made of stainless steel and are usually large and heavy, so preferably on the floor not in a loft.

If you or anyone else might later get a gas boiler, buy an indirect cylinder that can later be plumbed to a boiler. Modern unvented cylinders are very well insulated and will stay hot for a couple of days, possibly more.