Where do the heat losses from it go? Into your house or not?

This situation may be one I'm faced with in the not too distant future as my log gas boiler reaches the end of it's life. I am also looking at other solutions too.
My similar sized accumulator is housed inside the heated envelope so makes sense to keep it, plus I have a heating system I like, whereby the CH remains on 24/7 for the whole of the heating season and having that buffer is necessary for this regime.
If I returned to oil, as you, my problem would be finding an efficient simple oil boiler that "likes" the batch burns to recharge the store, similar to the log boiler.
I have a plate heat exchanger for winter DHW and solar thermal for summer DHW. My solar thermal also pre-heats the input to the PHx during winter.
It'a all on a sealed system.

Apologies for the delay in replies ...can't see how to switch on 'Notification of Replies'.

Just come off the phone to a chap who's put in an oil-fired boiler with a heat store. This is his rationale. It actually makes a fair bit of sense to me but interested to hear others thoughts.

1) Condensing boilers are only at their most efficient (the 90%+ that the makers claim) when they are condensing. But condensing stops around 65 degrees which is way below were most boilers are set. Ergo oil-boilers setup with a high temperature than 65 degrees are much less efficient. Significantly, he claims.

Anyone else agree with this ?

2) Boilers also work best when they are working hard.

3) Boilers wear and tear improves when they run constantly and not cycling on and off.

So he has a heat store that is heated by an oil boiler. The heat store then supplies the heat required by the underfloor heating and radiators. He has two sensors on the tank. One at the top set to around 70 degrees or so and one at the bottom set to around 50 degrees. When the top temperature is reached the boiler switches off. It restarts when the lower temperature limit is reached. So between those two 'events' the boiler remains off. (He did admit that he got a little bit of cycling towards the end of the heating phase).

The size of the boiler is small. Much smaller then the one specified for a 'traditional' system and he's thinking that even the one that he has is a bit over-sized.

It does mean that his radiators are running cooler than their design temperature and I've not got my head around that one yet...seems to suggest that larger radiators in each downstairs room would be needed in the absence of UFH. So there's a trade-off there to be worked out.

For DHW (domestic hot water) he has a coil in the bottom part of the tank and this forms a complete insulated secondary return system which constantly circulates his DHW. So no dead legs. No wasted water and instant hot water.

Of course his heat store is only three years old and so significantly better insulated then my 2002 fibreglass wrapped monster.

Thoughts anyone ?

Posted By: countrymanIt does mean that his radiators are running cooler than their design temperature and I've not got my head around that one yet

It is just multiplication really.

https://ostroykevse.com/Otoplenie/31En.html

Posted By: gravelldI didn't think oil boilers modulated at all...? Some sort of buffer is therefore useful for oil boilers, and a TS can fill this need.

Just a very quick search "modulating oil fired boiler" gave
Weishaupt Thermo Condens oil-fired condensing boiler (WTC-OW, 6 to 15 kW)
Weishaupt oil-fired condensing boilers use almost all of the energy stored in the fuel, converting it efficiently into heat. A condensing boiler uses the energy which in older heating systems is lost to atmosphere with the flue gases. In so doing, nett efficiency is increased to 105 % compared to 95 % for low-temperature systems.
.......The boiler benefits from modulating operation, having an infinitely variable response to current heat demand between 6 and 15 kW.
.......Particularly quiet: Just like a gas-fired condensing boiler, the boiler is almost completely silent thanks to its modulating operation and innovative preparation of the fuel/air mixture.

Of course there must be others in the market place. It would seem that modern oil boilers are up to the same standards of efficiencies as modern gas boilers. So with the quick 'for example' above I would have thought a TS would not be needed.

Interesting there are some developments in this area. Here's something else pertinent, PiH, which might not have come up in your search due to your location:

https://www.worcester-bosch.co.uk/professional/news/erp-regulation-update
The major stumbling block is on the modulation of an oil-fired boiler. Generally speaking, certainly in the UK, a domestic oil-fired boiler typically has a fixed burner, a non-modulated burner.

But probably better to build or fix the house such that burning T-Rex bones isn't required.

Posted By: Peter_in_HungaryThe competitive market place for oil boilers IMO is LPG and wood, pellet or as from another thread turf.

Or a heat pump.

Oops just the read the OP properly. In my opinion TS are great for combining inputs from different heat sources, but are just one big, albeit inefficient, radiator when heated by just an oil boiler.

Modem oil boiler will condense if operating with a low temperature flow, when a TS is used to heat DHW, it needs to be kept at a high temperature. Hence using a thermal store for DHW is not a good option with a modem oil or gas boiler.

It needs a low temp return - this is the water that does the condensing before it warms up in the boiler - ideally the flow rate needs to be as low as the boiler allows. I've seen boiler specs allow a 20 degree C raise (this allows 40 degree return, 60 degree flow for example).

For my hot water I plan to use a simple regular condensing boiler, fix the flow to the minimum specified, mix the return with the flow to have a fixed minimum return temp into the boiler and therefore feed into the tank/store only water at the desired temperature for DHW in a single lift.