Heating DHW with oil vs night rate electric

System

This discussion was created from comments split from: 10kWh LifePO4 DIY Battery Addition..... Here is my write up..

graememk

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

https://www.youtube.com/watch?v=e7GzLi6ZquI

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

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.

randombar

https://www.boards.ie/discussion/comment/119589772#Comment_119589772

What price of oil, per litre or what?

graememk

https://www.boards.ie/discussion/comment/119591098#Comment_119591098

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!

randombar

https://www.boards.ie/discussion/comment/119591156#Comment_119591156

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?

graememk

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

"Heating DHW with oil vs night rate electric"

https://www.boards.ie/discussion/comment/119592832#Comment_119592832

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.

Jonathan

https://www.boards.ie/discussion/comment/119593116#Comment_119593116

Done. Shout if I missed any posts.

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…

yankinlk

https://www.boards.ie/discussion/comment/119593658#Comment_119593658

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.

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.

randombar

https://www.boards.ie/discussion/comment/119593116#Comment_119593116

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

https://www.boards.ie/discussion/comment/119593658#Comment_119593658

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.

https://www.boards.ie/discussion/comment/119594097#Comment_119594097

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

yankinlk

https://www.boards.ie/discussion/comment/119594097#Comment_119594097

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!

bullit_dodger

https://www.boards.ie/discussion/comment/119594739#Comment_119594739

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 :-)

graememk

https://www.boards.ie/discussion/comment/119594911#Comment_119594911

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.

https://www.boards.ie/discussion/comment/119594167#Comment_119594167

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.

yankinlk

https://www.boards.ie/discussion/comment/119594911#Comment_119594911

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.

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 : Amazon.co.uk: DIY & Tools

Punchin A Keyboard

https://www.boards.ie/discussion/comment/119594739#Comment_119594739

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.

graememk

https://www.boards.ie/discussion/comment/119595061#Comment_119595061

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.

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.

Ta

bullit_dodger

https://www.boards.ie/discussion/comment/119595439#Comment_119595439

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 :-)

graememk

https://www.boards.ie/discussion/comment/119595439#Comment_119595439

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.

randombar

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

unkel

https://www.boards.ie/discussion/comment/119593688#Comment_119593688

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

graememk

https://www.boards.ie/discussion/comment/119611704#Comment_119611704

I have something like this https://www.amazon.co.uk/Heater-Control-Neutral-Required-Gateway/dp/B0963KS4YC/

randombar

https://www.boards.ie/discussion/comment/119612128#Comment_119612128

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.

graememk

https://www.boards.ie/discussion/comment/119612211#Comment_119612211

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.

loyatemu

https://www.boards.ie/discussion/comment/119612079#Comment_119612079

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.

unkel

https://www.boards.ie/discussion/comment/119612392#Comment_119612392

I just switched to Energia. Fixed night rate for the next year is 7.9c / kWh incl VAT. I just checked with bonkers.ie 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

loyatemu

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

DC999

@unkel, +1 to that!!

unkel

https://www.boards.ie/discussion/comment/119612727#Comment_119612727

It's their EV plan. The only electricity contract in Ireland that does NOT have variable prices, but fixed prices for the entire duration of the contract. That is worth quite something as I doubt we have seen the end of the huge price increases yet. I re-signed up for this plan about a week or two ago, it has since gone up in price twice though 😮

https://www.energia.ie/plans-and-switching-info/ev

randombar

https://www.boards.ie/discussion/comment/119612818#Comment_119612818

Trying to estimate the pros and cons of breaking from bord gais at the moment to switch to this. To be fair to bord gais they were the only ones that didn't increase their standing charge.

bullit_dodger

https://www.boards.ie/discussion/comment/119612668#Comment_119612668

Thanks for doing the legwork there. The upshot for me is that I'll be closing that valve from the heating system into the heat exchanger coil in the hot water tank in the hot press. I always used to view that as "free hot water" when I had the heating on, but in reality it's still taking energy to heat it, and that energy could be more cheaply supplied at night rate.

unkel

https://www.boards.ie/discussion/comment/119612894#Comment_119612894

Yes you need to do some quick sums. In my case it was very easy. My previous provider had just announced another major price increase. I use a lot of electricity, but most of it at night. So the supercheap 7.9c incl VAT per kWh swung it for me, well worth paying the €50 penalty.

yankinlk

https://www.boards.ie/discussion/comment/119612079#Comment_119612079

Holy-quoting-me-out-of-context mate. I was commenting way way way back where someone tried to shutdown the thread for mentioning fossil fuels.

randombar

So had a look at my heat loss from my tank (thanks to Home Assistant).

https://capture.dropbox.com/ELQt2mgNgGbwhZ4H

Safe to say from midnight to 8 the first day all losses were natural i.e. no showers were had etc.

bullit_dodger

Your tank losses are pretty good. 54C->45C (9C loss) in 18 hours is pretty low. My own one, which is just an old copper tank with 2x lagging jackets on it loses about 25C/day, so nearly 2x the losses you have.

If the profile you posted is normal (i.e. someone having a shower at 7am ?), I'd probably move your scheduled heating (boost) time from daytime to 6am and take advantage of the night rate.

DC999

Yeah, and you still have 45c water in evening from the night rate.

We've only the auld skool cooper tank too with a lagging jacket. So cancelled our Eddi as would be a huge radiator in summer. In our bedroom that is already too warm then. And if you're losing a lot of heat, you're using power that could have gone elsewhere.

randombar

https://www.boards.ie/discussion/comment/119625567#Comment_119625567

Stupid question but are those new tanks expensive? Would it be worth an investment?

1 shower in the morning and 3 showers in the evening. Everyone loves loads of showers apparently!!!!

bullit_dodger

https://www.boards.ie/discussion/comment/119625684#Comment_119625684

New tank for me? No probably not worth it, and if you meant yourself.....your losses randombar are very good, so whatever you have there currently you won't get much improvement with a brand new tank. As per your profile (assuming that's a normal day?) it looks from the energy in/out chart you posted above that you brought the temp up to the tank before midnight, I'd change that so that

• it heats it up at 6am, that way it'll be hot for that 1st person in the morning at 7am.

No sense in heating the water before midnight (at day rate) and having it sit there loosing heat until 7am. I'd then

• have it boost at 8:30am to bring it back up to 55c using the last of the time that you have night rate.

Naturally when or (if?) the hour goes back in Oct, you'll have to move that one back an hour as night rate ends at 8am in the winter.

Your losses are low, so that boost at 8:30am should see you right for the 3x showers later. Should save you a few quid....

unkel

@bullit_dodger - "your losses randombar are very good"

Are they? My hot water cylinder (well insulated 360l one from Joule from 2016) is supposed to lose only 1C per 24h. I haven't measured this mind. No idea how much it cost, it was part of a larger upgrade incl. subsidised solar thermal install at the time.

slave1

I have a factory insulated 240L cylinder, I just know in my heart and soul it's not great at heat retention but the eye watering upgrade costs put me well off as I doubt financially viable, shame as I'm not a lover of inefficiency

bullit_dodger

https://www.boards.ie/discussion/comment/119626588#Comment_119626588

LOL - it's all relative mate. His loses are very good compared to my old piece of shite immersion tank which loses 20C a day!!

Could my one be improved? Course it could! Although I already have 2x laggin jackets on it, but it's one of those things that the law of diminishing returns kick in and for me, it's not worth spending couple hundred Euros swapping out the tank to improve something which I don't even use all the hot water I have. I'd say if your losing less than 8-10C a day your probably doing ok. Less is better of course, but I'd probably question spending €500 (or more?) on a tank to give you marginal better losses.

unkel

Oh I agree. I came from the other way round. We needed to upgrade our standard 120l cylinder (family of 5) as it was empty in 8 minutes (one shower) LOL with our pumped showers. So we needed a big cylinder anyway, so you might as well get a well insulated one and then we went for the complete solar thermal install as there was a large subsidy attached to it.

Jonathan

A few more data points for you. My (250L factory insulated) cylinder heat loss over the last 12 hours. Eddi and Solar Thermal heated entire cylinder to 60°C yesterday. The higher heat loss figures for bottom cylinder sensor around 21:50 and 00:00 were people washing hands etc before bed, but otherwise no major water usage during the period.

graememk

https://www.boards.ie/discussion/comment/119629779#Comment_119629779

The joule that I have I'm seeing roughly the same.

YFlyer

I assume heating the DHW tank is still cheaper with gas compare to night rate electricity?

graememk

https://www.boards.ie/discussion/comment/119630422#Comment_119630422

Depends on how low your night rate is and how high the gas price is.

eg energia's price rise gives a gas kwh price of 12.07c inc vat, (assuming a 15% discount that they are giving)

heating DHW say 90% efficiency gives a comparable rate of 13.9c /kwh

My night rate is currently (and fixed at) 7.9c so yes in that case, it is cheaper. But it all comes down to what price you currently pay for gas and night rate.

bullit_dodger

Anyway you could test that statement unkel about the 1c/24hrs loses. While I'd like you to be right, it seems too good to be true? No?

Or to phrase it another way, it's saying that if you heated your tank up to 60c, after 3 weeks (!) it would be 40C. Doesn't seem plausible, does it? Again, those new well insulated steel tanks are indeed the business, but 1C/24hrs seems almost too good to be believed.

randombar

By the way my tank is one of those big tempest solar tanks.