# Cheapest way to heat water?



## Hillsalt (18 Mar 2010)

Summer is coming.
I have a oil fired central heating system for a 5 bedroom house. During summer, I switch off the radiators and set the timer to come on for an hour in the morning so we can have showers. There is also an electric emersion  in place. Would it be more cost effective to use the electric timer?

Thanks in advance.


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## DGOBS (19 Mar 2010)

Nope, oil would be the cheaper option, but it would be better if you had a valve fitted (may already be one) that would totally shut off your central heating (as opposed to shutting all the rads off individually) so you don't have your boiler heating the rad circuit of your system wasting fuel.


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## rockofages (19 Mar 2010)

I don't know about oil, but for gas the maths (in my case) are simple:

The hot water tank is 150 litres.

Electricity on nightsaver costs ~7c a unit. The immersion heater is almost 100% efficient.

Gas is ~4c a unit, but the boiler is only about 75% efficient. So it's over 5c to get 4c worth of heat.
I too cannot turn off the water to the whole system, so I am heating probably another 150 litres of water (ie double) which circulates in the system. We're now over 10c to get the 4c worth of heat.
Heatloss from the water circulating in the system is probably adding another 2c.
Total is now up to maybe 12c.

Not very scientific, but enough to prove nightsaver electricity is cheaper than gas.


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## quentingargan (20 Mar 2010)

rockofages said:


> Electricity on nightsaver costs ~7c a unit. The immersion heater is almost 100% efficient.
> 
> Gas is ~4c a unit, but the boiler is only about 75% efficient. So it's over 5c to get 4c worth of heat.
> I too cannot turn off the water to the whole system, so I am heating probably another 150 litres of water (ie double) which circulates in the system. We're now over 10c to get the 4c worth of heat.
> ...


 
Interesting figures. Unless you have a condensing combi stove, I would always argue that using the central heating system to heat a 120L cylinder is very inefficient. 

But unless the cylinder is incredibly well insulated, nightsave electricity for 120L (which is a typical cylinder) won't get you past bath-time. 

Your figures highlight why solar panels work well - at a time of the year when the central heating is off, (and hot water is therefore at its most expensive), the solar panels are working at their best. 

Depending on your views on energy inflation, and the cost of installing in a particular situation, solar is the cheapest way in that after the capital cost, it is free. There are those who will dispute this, but in many situations it is true.


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## bullworth (20 Mar 2010)

I have Gas central heating and  a rad in every room. If nightsaver energy is cheaper, how much would it cost to convert my system ? It seems like a lot of plumbing would be necessary to remove my old rads etc.
Could I plugin an electric rad in the sitting room and run it cheaply off nightsaver electricity yet keep my gas and existing rads with plumbing  as a backup at the same time ?
My sitting room only has one rad and with a baby on the way and the missus always freezing (with the expensive gas fire running daily) Ive been thinking about how best to heat the room whether with an extra radiator connected to my existing system or maybe getting some other form of heat. Personally I'm used to sitting in the cold as I'm quite warm blooded but I have others to think about now. Baby will arrive in September so I need to be ready for the next winter. Any suggestions ?


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## quentingargan (20 Mar 2010)

bullworth said:


> I have Gas central heating and a rad in every room. If nightsaver energy is cheaper, how much would it cost to convert my system ? It seems like a lot of plumbing would be necessary to remove my old rads etc.
> Baby will arrive in September so I need to be ready for the next winter. Any suggestions ?


You've been hearing too much about babies that don't sleep at night. Nightsaver will only work between midnight and 9.00am (or 11pm to 8 am in winter). Unless you're planning late nights, an electric radiator is going to cost you 14c per KwHr. 

The point about water heating with the boiler is that it is inefficient because you are heating a boiler, flue, pipes etc., all to heat a small hotpress cyliner. 

Your gas central heating should provide plenty of heat. You may have the radiators badly balanced so that the one in the sitting room is cooler than other ones, or it may have been badly dimensioned in the first place, (or may have air in it). 

However if it is cold with the gas on all the time, I would look at insulation, draught-proofing etc. as a start point, rather than plumbing in a second radiator. On the other hand, if the radiator is badly sized, you could just put in a double one to replace a single, or a longer one.


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## rockofages (21 Mar 2010)

bullworth said:


> I have Gas central heating and  a rad in every room. If nightsaver energy is cheaper, how much would it cost to convert my system ?


No, you're not understanding correctly. Gas is cheaper for heating the house, but nightsaver electricity is cheaper in a typical (older) house for heating the hot water.



			
				quentingargan said:
			
		

> But unless the cylinder is incredibly well insulated, nightsave electricity for 120L (which is a typical cylinder) won't get you past bath-time.


It is well insulated, but we all shower in the mornings, with a low-flow showerhead. There is enough warm water left in the evenings to do the wash up. (And that's on "sink"!)

It actually works out incredibly cheap. 2kW heater, on for 30 mins a day, means 1kW/h a day. 7c x 365 = less than €26 per annum for most of our hot water needs. (If the system was on "bath" it would be 2.5 times the price, or a bit less than €65 a year.)


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## quentingargan (21 Mar 2010)

rockofages said:


> It is well insulated, but we all shower in the mornings, with a low-flow showerhead. There is enough warm water left in the evenings to do the wash up. (And that's on "sink"!)
> 
> It actually works out incredibly cheap. 2kW heater, on for 30 mins a day, means 1kW/h a day. 7c x 365 = less than €26 per annum for most of our hot water needs. (If the system was on "bath" it would be 2.5 times the price, or a bit less than €65 a year.)


 
Good on you, but you are a lot more frugal than most. The average household uses about 40L of hot water per person per day, and many houses use a lot more than that. 

Your daily quota of 1Kw hr produces about 22L of hot water brought from 12 degrees to 50 degrees, and that isn't accounting for heat losses etc. Indeed, you would be using very little of your cylinder's capacity at that.


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## bullworth (21 Mar 2010)

quentingargan said:


> However if it is cold with the gas on all the time, I would look at insulation, draught-proofing etc. as a start point, rather than plumbing in a second radiator. On the other hand, if the radiator is badly sized, you could just put in a double one to replace a single, or a longer one.



Thanks . I have been looking at draughtproofing but Im fairly well draughtproofed as it is . The problem is the missus is always freezing even when I am warm. I might go for adding in a second radiator. The immediate problem is where to site it.
The present radiator is placed underneath the window and can often be blocked by a couch which might be part of the problem. 



rockofages said:


> No, you're not understanding correctly. Gas is cheaper for heating the house, but nightsaver electricity is cheaper in a typical (older) house for heating the hot water.



Thanks for the explanation. Is nightsaver something you need to ask the esb to change you over to  or does it just mean switching on your immersion after midnight ? Is it cheaper to make hot water for my household by switching the immersion on late at night than to use gas the next day ? I have Gas central heating and hot water but I also have  an electrical immersion switch with options to heat it up to ''sink'' or ''bath'' using the esb.

The problem I have always had with immersions is forgetting to switch them off. Frequently they end up being forgotten about and left on for 12 to 24 hours until the on setting is realised. I have no idea why I havent seen one with a timer switch instead of just two switches ''sink'' and ''bath''.


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## DGOBS (21 Mar 2010)

Buy her a big thick jumper and save the planet!

(my wife wonders why the room thermostat stops at 30degs!)


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## seantheman (21 Mar 2010)

DGOBS said:


> Buy her a big thick jumper and save the planet!


 
Jeez, it goes way over my head when plumbers get technical


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## rockofages (22 Mar 2010)

bullworth said:


> Thanks for the explanation. Is nightsaver something you need to ask the esb to change you over to  or does it just mean switching on your immersion after midnight ?


Nightsaver requires ESB Networks to install a dual rate meter. It'll cost you nothing. You get charged a slightly higher standing charge but you get half price electricity at night (11pm-8am in winter, midnight-9am in summer). Use of timeswitches means the washing machine, tumble dryer, dish washer and immersion heater can all be set to use cheap electricity. We have probably reduced our electricity bill by 25-30% by using Nightsaver.

If you get your electricity from Board Gais or Airtricity the Nightsaver still works, and you save an additional 10-14% over the ESB prices.


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