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Heating DHW with oil vs night rate electric



  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    Heat geek have installed solar tubes to heat a buffer tank which runs the heating for the office.

    They've put a load of monitoring on it.

    And as a reminder for anyone that's on oil. if you night rate is less than the price of oil/9 (maybe even 8 depending on your boiler!) Its cheaper to heat your DHW with an immersion on night rate

  • Registered Users Posts: 64,347 ✭✭✭✭unkel

    Not just heat your water, your home too (during night rate hours). Obviously if you have poor insulation this is a bit of a waste though.

  • Registered Users Posts: 3,331 ✭✭✭randombar

  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    Per litre

    There's about 10kwh of heat in a litre,

    You'd be hard pushed to get 90% efficiency heating to 60c. And might even only get about 80!

  • Registered Users Posts: 3,331 ✭✭✭randombar

    That's a very interesting one:

    €1.35461 per litre for Kerosene -> €0.1693262 per kwh (80%) / €0.15051222 per kwh (90%)

    €0.09864 per kwh bord gais (I think that went up last week but I don't know values)

    Issues/Things that I can think of:

    Shower in evenings so no point having the hot water warm in the morning.

    If heating the house is it more efficient to heat both house and hot water?

    If using batteries to heat hot water need to take battery losses into account I guess? So would be €0.1233 per kwh

    Dont want to be thread stealing so anywhere else this is being discussed?

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  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    @Jonathan by any chance could this be spun out into a new thread

    "Heating DHW with oil vs night rate electric"

    There's a lot of "it depends" 😂

    If you have a well insulated tank, it doesn't really matter,the losses are very little. I have one and it's more like 5 degrees in 24 hrs.

    But different tanks vary!

    If from batteries.. mid day could be the best, if it's not winter, a good chunk of it will be via solar.

    As for more efficient.. how is your system plumbed/controlled?

    Do you have a condensing boiler?

    Condensing boilers work best at lower temperatures.. but DHW needs to be >60.. or at least 55 at least once a week..

    Friends house is plumbed with the feed from the oil boiler goes through the hw tank then round the house... Great in winter but in summer the house is too hot when they need hot water! Yeah gonna get them to change that to either s plan or y plan.

    There's fancy things like hot water priority on gas where it goes flat out for hot water then modulates down for space heating so it can stay in condensing mode.

    Modern oil boilers can have efficiencies of around 85% to 95%. A new condensing oil boiler will typically have an efficiency of at least 90% while a non-condensing oil boiler will be around 85% efficient.

    Older oil boilers tend to be 60% to 70% efficient.

    .. mines 25+, could be even 30+... But it got a new burner 5 or 6 yrs ago now.

  • Moderators, Education Moderators, Home & Garden Moderators Posts: 8,039 Mod ✭✭✭✭Jonathan

  • Moderators, Sports Moderators Posts: 18,478 Mod ✭✭✭✭slave1

    Are we seriously debating using fossil fuel to heat water versus night electricity with its renewable credentials on a Renewables Forum?

    There's more outside our own financial awareness at stake here…

  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    We are. The conversation has to start somewhere. If you want to change peoples habits you have to educate them. I for one cannot afford an expensive heat pump retrofit on my 40+ year old home. I do my best to leave off the boiler until Nov,Dec but I would never have done that before coming here and learning what an eddi can do ... Still learning.

  • Registered Users Posts: 1,963 ✭✭✭jkforde

    "Friends house is plumbed with the feed from the oil boiler goes through the hw tank then round the house... Great in winter but in summer the house is too hot when they need hot water!"

    huh? I'm speechless, maybe an energy price shock is what society sadly needs to cop on.

    🌦️ 6.7kwp, 45°, SSW, mid-Galway 🌦️

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  • Registered Users Posts: 3,331 ✭✭✭randombar

    Well insulated tank with solar thermal and a grant condensing boiler.

    Definitely more at stake here but I think everyone on here will take the maths/advice and be able to spread to other people who can't afford to make the tough decisions, i.e. I'll be telling the lads down the pub, if you've an old boiler and night saver use the immersion to save a few quid.

    My mothers house was the same, was a lot cheaper than she thought it would be to introduce a HW zone.

  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    All too common id say in Bungaalow Bliss land. Mine was like that - retro fitted a zone. I really think gov grants should target smaller Retros as a prioroty rather than the "all-in-on-everything" idea. Insualtion, Windows, Zoning, Controls all worthwhile and can be approached as indivual projects. togetehr they add up to a big difference!

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    And they have no radiator controls (on the actual radiators?) which they can turn off?

    That seems odd no? Too odd to believe if I'm honest - but I've been wrong before :-)

  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    I'd say a lot don't even have TRVs and I'd put money on a lot not even having a thermostat.

    I only put in a thermostat last year when I put in a tado system.

    Thermostatic valves were put in after my grandfather passed in 06.

    You'd be surprised with what's out there.

    If your tank is well insulated you'll not have a problem carrying the heat from the morning.

    I'd have it knocking off just before night rate ends.

  • Registered Users Posts: 2,727 ✭✭✭yankinlk

    not untill i started fitting them. i dont know if rad controls even existed when my house was built... DIY not part of an estate if thats whta yer thinkin.

  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    I mean I totally get the 1 zone thing for the house that the hotwater could go through the heat exchanger in the HW tank and then out to the rads. It's odd, but not insane - but to not have a value on each radiator to control the heat in each room by simply being able to turn up down the radiator in a room is crazy. Even 100 year old houses have that!

    Still, I'm always surprised with what's out there! Cowboys Ted! :-)

    Ps:- As Graeme mentions above, the Tado devices are excellent folks if your interested in curbing your heating consumption.

    tado° Smart Radiator Thermostat - WiFi Starter Kit V3+ - 2x Smart Radiator Valve, Digital Heating Control Via App, Easy Installation, Save Energy - Works With Alexa, Apple Siri, And Google Assistant : DIY & Tools

  • Registered Users Posts: 72 ✭✭Punchin A Keyboard

    I am in one zone land pushed off heating controls upgrade as part of bigger upgrade e.g. windows. Some grants are there but only via the one stop shop bollocks which is the route i am heading down but it is a painfully slow process.

  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    Well there was valves but the old bog standard ones.

    I could split my house into 2 zones if I wanted to but now with the tado I don't have to.

    The temperature values from the smart is good enough. But I am considering getting one or two more maybe for the hall and kitchen to see if it's any different in readings.

  • Registered Users Posts: 1,377 ✭✭✭DC999

    Any idea how to stop the boiler heating the hot water tank by turing off the feed from boiler to it? We've a Nest but when it's on it heats both tank AND rads. Boiler maybe 15 years old. Nest newer of course. Don't have a 2nd zone for hot water tank only.

    Did ask fella servicing boiler and said it was a 'big job, not worth it' to get a 2nd zone. Few years back and gas prices have climbed since.

    There's deffo no 2nd zone setup. And we don't need it. I am assuming I can tun off the value from boiler feeding bottom of hot water tank. And that 'spur' then goes dead. Anyone any idea if that will cause issues? We never use hot water from tank. So pure waste to heat it.


  • Registered Users Posts: 2,344 ✭✭✭bullit_dodger

    Every heating system is "unique" in Ireland, but usually (if it's plumbed standard enough) there should be 2 pipes going in at the bottom of your tank. One will be the cold water from the attic, and the other will be the hot water. Easy enough to determine which is which as if you turn on the heating for 2-3 mins one will get warmer of course.

    There should be a valve on that somewhere close to the tank. Not always, but that's typically where they locate it. If you turn that off then in theory if they've isolated the tank correctly that should stop heating the tank.

    One good thing about heating is that if you are slow and methodical, you can usually figure out everything and if something stops working, well you simply reverse the last valve you changed :-)

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  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    Yeah you should be able to just turn it off, if you have a valve to turn at your tank..

    Lengionella shouldn't actually be much of a concern as your not drinking or washing in that water. Also that it's never warm, just cold.

    Just goes to show the mis mash of heating controls.

  • Registered Users Posts: 3,331 ✭✭✭randombar

    What are the options to control the immersion apart from an Eddi? Something to plug into the home assistant.

  • Registered Users Posts: 64,347 ✭✭✭✭unkel

    Nobody is talking heat pump. Simply heating the water with the electric immersion at night rate hours. Which is cheaper than heating with oil or gas. And far more environmentally friendly as night rate electricity is already on average over 50% from wind

    My hot water tank is well insulated, it is supposed to only drop 1C per 24h in heat losses

  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

  • Registered Users Posts: 3,331 ✭✭✭randombar

    Why on earth is the Eddi so big if all that's needed is a small controller?

    Just nervous of the power going through these things.

  • Moderators, Home & Garden Moderators Posts: 5,519 Mod ✭✭✭✭graememk

    That's a dumb switch/relay on or off.

    An immersion is only about 13 amps. Plenty of head room in it.

    An eddi can vary the power going to the immersion. By varying the voltage.

    An immersion will always pull 13 amps.. but if the voltage is only 10v it will only draw 130w.

    It has switching between two elements, power monitoring etc etc.

  • Registered Users Posts: 14,574 ✭✭✭✭loyatemu

    Smart Meter EV plans might be approaching the cost of gas (considering the differences in efficiencies) but that's offset by higher day rates. Standard Day/Night is way more expensive than gas.

  • Registered Users Posts: 64,347 ✭✭✭✭unkel

    I just switched to Energia. Fixed night rate for the next year is 7.9c / kWh incl VAT. I just checked with and the cheapest gas price currently available is 8.6c / kWh incl VAT. Electricity is 100% efficient for heating water, gas 95% at the very best (more like 80-90% with a modern condensing gas boiler), this makes the difference between the two rates even bigger

    Then there's the environmental aspect. With electricity being over 50% renewable / zero emissions at night and gas 0% renewable, 0% zero emissions

    So, unless it really doesn't suit (i.e. if you have an ancient hot water cylinder that is not insulated well and you only ever use hot water at night, before the night rate kicks in), everyone really should heat their hot water with electricity

  • Registered Users Posts: 14,574 ✭✭✭✭loyatemu

    OK - I was going off the new prices here and that plan isn't listed. What's the daytime rate?

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  • Registered Users Posts: 1,377 ✭✭✭DC999

    @unkel, +1 to that!!