Thermal stores - any experience


Were probably going to do an extension next year and will also be replacing the oil boiler so it’s an opportunity to modernise the heating system and upgrade the insulation.

Currently I have an ancient oil boiler, which works but is probably about 25 years old, in the last few years it’s been a secondary or occasional system, most of the space heating is done with a boiler stove so when I’m getting a new condensing oil boiler in im pondering a thermal store tank, maybe something like this: … tores.html

I would like to store heat from the stove and the boiler and also maybe have an additional coil for solar to perhaps be installed at a later date.

Anyone got any experience with them? Is it possible to directly heat the tank and not the house from all the sources (not neccessarily at the same time)?



I dont have any experience with them but friends do and im not sure if they were overly impressed.
While im not a fan of oil heating would you consider a condensing oil boiler. New one are fairly efficient


Condensing boiler is a no brainer, but gas doesn’t make sense for my use case, the oil boiler is a secondary system, 75% of the heat is supplied by a boiler stove. I use about 500L of oil per annum currently or €300 worth in todays market. If I had gas I would incur nearly €100 of standing charges if I never turned it on, and oil boiler servicing is a lot cheaper and is only required evey 4-5 years because usage is so low.

Lets suppose I did get a gas boiler, would I still have to get it serviced every year despite such low usage? No use posing that question to someone in the trade, like asking a barber if I need a haircut.


There’s no legal requirement, as far as I know (assuming you’re living there, not renting it out) but it is advisable. Mind you, I think it’s advisable to service oil boilers yearly, too, and no doubt there are guidelines for stoves, too.

Have you looked at what your stove costs to run? Just using a gas boiler for everything may be cheaper.


By the way, 500 liters of oil is equivalent to about 5000 kWh. Gas is about 4c/kWh, so, plus the 100 euro or so service charge, you’d be looking at about 300 euro for that gas usage, too (barring any discounts from combined gas electric plans, etc, but those usually aren’t worth much). Benefits being that you wouldn’t need a tank, to organize deliveries, etc. Of course, if your usage falls any further, oil does become relatively cheaper.

One other thing to note is that gas prices have historically been much more stable than oil prices. Oil is relatively cheap now; you’d have been paying a fair bit more five years ago (looks like it was about 400 euro per 500l). It’s probably more likely to rise dramatically than gas is, tho.


Indeed I was paying over €1 a liter at one point and I didn’t have a stove at the time, the bills were eye watering.

The SEAI claim gas is costing you between 6.6 and 9.2c/kWh as a best case scenario, depending on usage. … risons.pdf
(second page looking at 90% efficency)

Stove running costs are about €1000 for wood approx 12m3 (or 4.5 metric tonnes), a 50:50 mix of soft:hard wood @<20% moisture. 2 x services a year €120. Of course working out the delivered cost per k/Wh isn’t easy.

The SEAI give the delivered cost of bulk softwood @25% mositure burnt at 80% efficency as 6.39c/kWh but mine is <20% mositure so it would be better than that. They don’t give figures for bulk hardwood, only on pallets or bags and the stuff on pallets tends to be kiln dried which is much more expensive and not worth it IMO.

The only way I can compare is looking historically at the demand from the house, a typical winter would see us going through 2500L or €1500 @ 60c/L but we have since improved the insulation and use the heat a lot more so €1400 today for maybe 20% more usage.

And yes there is a lot of work getting wood delivered and stacked into the shed, I plan this for sunny Saturday afternoons in May and June when the suppliers are desperate for orders and it gets another season of drying in my shed. The last thing you want is a pile of slimy wet wood out the back that needs to be stacked into the shed on a cold february night.


I think those SEAI gas costs actually include the standing charge (which is why they vary with usage).