Renewable Energy: oil boiler pellet hybrid system

1 to 22 of 22

- CommentAuthorNoodle
- CommentTimeNov 29th 2022 edited
Hi all,

We have a trusty (or very temperamental) pellet boiler that serves our house and a converted barn used as a holiday let. Its connected to a big 2000l buffer tank.
As its not hugely reliable after 7 years, and no very slow/ expensive service from EU suppliers these days.. we have finally installed a "backup" oil boiler that can be switched on linked to the buffer tank with the biomass switched off.

Now coming to order my 5Tonnnes of blown pellets @ Â£550!!!per T it works out that oil is about 20% cheaper.

My main question is if I hand over to the oil system boiler for winter, should I really bypass the buffer tank altogether so I don't waste a loads of energy heating up the buffer tank? We get thro0ugh 15Tonnes pellets a yr for a 5 bed house + 3 bed holiday let..im starting to think the system isn't working very efficiently as that equals about 8000L of oil a year..

Any thoughts appreciated.
- CommentAuthorNoodle
- CommentTimeNov 29th 2022 edited
this is the system by the way. perhaps its a 1000l buffer, but the stats have never worked properly so I just have 1 that keeps the middle around 65 degrees...i mean, that could also be part of the problem!!

The problem with the system I have is that the Barn UFH is taken off mid height but the buffer water there cools down quickly vs the top and so if I put the pump stat at the top 1/3 the barn UFH supply quickly cools to mids 50sC while the top take off is still at 65+ .
- CommentAuthorJeff B
- CommentTimeNov 29th 2022
I think you might have an issue with the oil boiler constantly cycling on/off if you remove the buffer tank? I'm sure more technically savvy folk than me will be along to advise you on this.

I fully understand your pain with the pellet boiler after having struggled with mine for over 7 years. The price for pellets that you quote is extraordinary - how can that increase be justified!!? The last lot I bought about 18 months ago was Â£280 per ton and I moaned about that. As you say 15 tons pellets is roughly equivalent to 8000 litres of oil which is a huge amount. We have a four bed detached place in a pretty exposed location and we used 3.3 tons of pellets p.a. - approx 1600 litres of oil. I sold my pellet boiler last summer and installed a new oil boiler, so I would say go for one while you can, before HM Government bans the installation of same, which I have read they are contemplating doing.
- CommentAuthorPeter_in_Hungary
- CommentTimeNov 29th 2022
Posted By: Noodlethis is the system by the way. perhaps its a 1000l buffer, but the stats have never worked properly so I just have 1 that keeps the middle around 65 degrees...i mean, that could also be part of the problem!!

The problem with the system I have is that the Barn UFH is taken off mid height but the buffer water there cools down quickly vs the top and so if I put the pump stat at the top 1/3 the barn UFH supply quickly cools to mids 50sC while the top take off is still at 65+ >

Your diagram is a bit confusing. You show the barn UFH coming of the center of the TS but also show it tee'd off from the top output. The house also has UFH and both have rads.

Posted By: Noodlethe Barn UFH is taken off mid height but the buffer water there cools down quickly vs the top and so if I put the pump stat at the top 1/3 the barn UFH supply quickly cools to mids 50sC while the top take off is still at 65+ .

This is what I would expect. You have stratification in the TS so the water does not mix (correct - it is not supposed to) You don' have much heat in the mid point of the TS (about 500 l) and the bottom will be at heating return temp. so probably only about 250 l of useful heating water - yes this will quickly cool down by 15 - 20 deg when the heating comes on.

65 deg is a bit hot for most UFH systems so I guess there are heat exchangers somewhere yes?

As Jeff said 8000 l oil or 15 ton pellets is a lot of fuel. Do you know where the heat is going? I have 2 houses on one boiler and have heat meters on each house to see where the heat is used. How far is each house from the boiler room, could there be a big heat leak between the boiler room and one of the houses? Have you done heat loss calcs for each house to see what you should expect?

From my experience stone / rubble buildings (making an assumption about the barn conversion here) take a lot to heat up. When we did tourist lets with such a house we closed for the winter because the business just wasn't worth the heating bills. Could this be a consideration in your case?

Oil boilers don't typically modulate, is this the case with the boiler you have installed? If so it may be worth using the TS to prevent short cycling.
It would be a fairly simple job to connect the oil boiler to the TS but provide a bypass to take the TS out to see the effect of with or without the TS. Easier to do at installation time rather than drain down later to make changes.

I am assuming the boiler / TS is in a boiler room and any heat loss is outside the heated envelope of the house. If this is the case adding insulation to the TS may help, perhaps read the manufactures bumf to see what the heat loss for the TS is and make a judgement.
- CommentAuthorNoodle
- CommentTimeNov 29th 2022 edited
thanks both.

Posted By: Peter_in_HungaryYou show the barn UFH coming of the center of the TS but also show it tee'd off from the top output. The house also has UFH and both have rads.

yes not quite right the diagram. The barn UFH comes off midpoint of buffer. Everything else for the rest of the barn, dhw tanks and main house comes off the top. Both house and barn have UFH ground floor and rads 1st floors. So barn UFH coming off the mid, house UFH off the top essentially.. Both UFH manifold mix returns to supply approx 45c flow temp.

Posted By: Peter_in_Hungarys Jeff said 8000 l oil or 15 ton pellets is a lot of fuel. Do you know where the heat is going?

yeah the barn is right next to buffer but main house goes down 30m of insulated underground piping, not alot of heatloss thou from memory. both house and barn are heated throughout the day to approx. 19/ 20C due to 1. holiday lets being occupied and people demanding stupid temperatures.... and 2. old farmhouse, slow to warm up and I WFH.
I think perhaps with relocating the barn ufh takeoff and other measure then could be looking more like 12 to 13 T. 15T was top estimate.

Farmhouse and barn have been insulated/ double glazing but listed so not to standards ( 40mm cork insulation, historic double glazing etc) and compromised.

Posted By: Peter_in_HungaryI am assuming the boiler / TS is in a boiler room

Yep, both boiler and buffer in an adjoining barn, which was insulated to a modest standard. I think I skimped on the buffer tank so could prob up its insulation and the pipework as well.

Posted By: Peter_in_HungaryOil boilers don't typically modulate, is this the case with the boiler you have installed? If so it may be worth using the TS to prevent short cycling.

at the moment the oil boiler links direct to the buffer tank so asusme short cycling wont be an issue?

Would you generally suggest then that the Barn UFH is teed off the top and then I don't have to heat the middle of the buffer tank so much and can leave it to stratify properly? During spring/summer I move the buffer stat to the top of the buffer tank as dont use UFH and barley used any pellets then.

Posted By: Jeff Bhe price for pellets that you quote is extraordinary

yep, couldn't believe it when they came to quote me. we have the oil boiler installed and running so think it maybe time for me to optomise this system, been putting it off for last couple of years!

Think this is the buffer tank actually: no idea if thats good insulation or rubbish!
https://www.buffertanks.co.uk/shop/1000l-buffer-tank-hispec

thanks both.
- CommentAuthorNoodle
- CommentTimeNov 29th 2022
photo
- CommentAuthorNoodle
- CommentTimeNov 29th 2022
Posted By: Jeff BI fully understand your pain with the pellet boiler after having struggled with mine for over 7 years. The price for pellets that you quote is extraordinary - how can that increase be justified!!?

rising oil prices for transport, and then most the supply chains for timber and waste were from russia/ ukraine...
it will likely look alot different in a yrs time but still!
- CommentAuthorNoodle
- CommentTimeNov 29th 2022
Posted By: Peter_in_Hungaryheat meters on each house

do you have a link to such meters?
- CommentAuthorJeff B
- CommentTimeNov 29th 2022 edited
Posted By: Noodle
Posted By: Jeff BI fully understand your pain with the pellet boiler after having struggled with mine for over 7 years. The price for pellets that you quote is extraordinary - how can that increase be justified!!?

rising oil prices for transport, and then most the supply chains for timber and waste were from russia/ ukraine...
it will likely look alot different in a yrs time but still!

IIRC the pellets I got came from Ireland or USA or Canada but if in your case from Russia/Ukraine then that's different. I often hear the "rising fuel prices" argument but I think that is an excuse for a rip-off.

Pellets from overseas are brought over in ship loads which must be thousands of tons per load. Even if the cost of diesel doubled (which it hasn't or any where near that) then the additional cost per ton cannot possibly have doubled surely? I realise the final journey for pellets would be by road but there could be 40 tons per load. If the price has gone from Â£280 per ton to Â£550 per ton then the total cost of the 40 ton load has gone from Â£11,200 to Â£22,000. So the extra fuel cost equates to Â£10,800 - pull the other one!

Or am I missing something obvious?!!
- CommentAuthorArtiglio
- CommentTimeNov 30th 2022
Iâ€™ve just been quoted Â£565 plus 5% vat per tonne for a 6 tonne blown delivery The reason given is that previously a good percentage of supply came from russia and this is lost to the market. However it rather looks to me as though somewhere in the supply chain itâ€™s been decided to track the gas price on a kwh basis, users are pretty much trapped. There being no scheme to limit the prices as in the domestic gas market. If this pricing extends to commercial users theyâ€™re going to especially hard hit.
- CommentAuthorNoodle
- CommentTimeNov 30th 2022
Posted By: ArtiglioHowever it rather looks to me as though somewhere in the supply chain itâ€™s been decided to track the gas price on a kwh basis

yep, It was always sold as it wouldn't track oil prices but ultimately it does just feel like profiteering and ALL pellet manufacturers will use global energy prices to justify increasing their prices.

I hadn't done a proper consumption/ cost comparison between oil and pellets for a long time till this week thou and oil is clearly cheaper again by some margin...I suppose 6 months ago when heating oil was 110p pellets were once again cheaper....
Yeah they know they got a customer who in most cases has no option but to buy their pellets!
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 1st 2022
Posted By: Noodle
Posted By: Peter_in_Hungaryheat meters on each house

do you have a link to such meters?

https://www.alibaba.com/product-detail/DN15-20-25-High-Accuracy-MBus_62214379734.html?spm=a2700.galleryofferlist.normal_offer.d_title.2a36bcee021mkZ#

The installation is intrusive and as a cheaper quick alternative perhaps measure the pipe temps. on flow and return at the TS output and at the house input to check that the insulation hasn't degraded over time. (Ditto TS to barn) To measure use either an IR thermometer or a clip on pipe thermometers. (I have the heat meters for billing purposes (rented house) and to measure the heat used (family house) so that when I move to a heat pump (future plan) I have some idea of the heat load to be able to size the HP)

Posted By: NoodleWould you generally suggest then that the Barn UFH is teed off the top and then I don't have to heat the middle of the buffer tank so much and can leave it to stratify properly? During spring/summer I move the buffer stat to the top of the buffer tank as dont use UFH and barley used any pellets then.

If the TS is supplying DHW as well as heating then classically the DHW would come off the top and the CH lower down so that the CH doesn't take heat away from DHW needs. (prioritises the higher temp water for DHW)

I would put all the heating together, either at the top (no DHW) or centrally (if TS also supplies DHW) If you can put 2 thermostats on the TS, one at the top to control DHW temp and one at the centre to control CH temp then this allows different temps for each application which may give efficiencies and out of the heating season the CH thermostat can be turned down so that just the top of the TS is heated.
- CommentAuthorNoodle
- CommentTimeDec 3rd 2022
Thanks Peter. I'm toying with the idea of getting a plumber in to rejig a little. In the meantime I have a question regarding its general working now.

Generally the buffer tank and boiler seems to struggle to bring it back up to temp while calling for heat load and seem to only do so once majority of heating circuits closed. This is an issue with both the pellet boiler and with the oil boiler which is currently being used. Ive attached a clearer diagram.

- As mentioned the 2 stat setups doesn't seem to work properly so i've been just using a single stat to keep it at the set temp

- In summer I put it in the top pocket (T1) and set to 60/65ish as only for DHW, worked great this year and used barley any pellets for 6 months.

- In winter I have historically been moving it to the central pocket (T2) to ensure the UFH takeoff for the barn stays above50/55. and set the stat to 65ish

- I have noticed that as cold water floods the bottom of the tank the middle cools down to 45/50ish while the tops stays in the 60s.

- I have wondered if the boiler flow is in effect being pushed into the store and the majority heading straight across to the DHW/Rads takeoff and so almost feeding directly to the heating circuits instead of heating the store up, as it doesn't have an internal coil/ baffle plate? Is this possible/ likley and if so, short of replacing the store with one with a coil would bringing the boiler feed in a little lower down help/ stop this?

-Finally to try and limit my heating load I have been setting the store to around 65 mid to avoid heating too much water too hot and the associated extra heat loss. Would I be better off heating the top or middle up to far hotter temperature in the hope that the boiler feed/returns are hotter and the store would have a larger heat buffer and not cool down as quickly when cold heating circuits flood the store? What temp do people normally heat buffer tanks upto?

-I do have a stat I don't currently use that temporarily stops the heating circuits if the store drops below a certain temp, maybe I should use that to allow the store to get back to a certain temp after it cools down before it starts pumping heat again?

Many thanks for any thoughts.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 4th 2022
Posted By: NoodleGenerally the buffer tank and boiler seems to struggle to bring it back up to temp while calling for heat load and seem to only do so once majority of heating circuits closed. This is an issue with both the pellet boiler and with the oil boiler which is currently being used. Ive attached a clearer diagram.

When I read you description of your heat load (5 bed house + 3 bed holiday let.) and saw the description on your boiler (20kw boiler + 1000 ltr TS) my initial thoughts was the boiler and TS are sized conventionally (TS = 50 x boiler capacity) but it seems a bit small for the heat load unless everything is well insulated.

Your comment quoted seems to bear that out. The TS will only be able to reheat using spare heat after the heat load is used so if the heat load is using most of the boiler capacity then little will be left to build up heat in the TS. I have always thought that for a batch burner i.e. a wood burning stove with a TS then the boiler should be about twice the capacity of the heat load to allow for some catch-up. This doubling factor is not needed with a gas boiler as it is a demand boiler and a pellet boiler is perhaps sort of half way between a gas boiler and a wood burner so some extra capacity will be needed if the TS is to be heated as well as the CH load.

Have you calculated your theoretical heat load?

Posted By: NoodleI have noticed that as cold water floods the bottom of the tank the middle cools down to 45/50ish while the tops stays in the 60s.

This is what I would expect if the TS is stratifying correctly. If you are taking heat out of the centre of the TS and returning to the bottom then the top of the TS should retain the heat without much change.

Posted By: NoodleI have wondered if the boiler flow is in effect being pushed into the store and the majority heading straight across to the DHW/Rads takeoff and so almost feeding directly to the heating circuits instead of heating the store up, as it doesn't have an internal coil/ baffle plate? Is this possible/ likley and if so, short of replacing the store with one with a coil would bringing the boiler feed in a little lower down help/ stop this?

The boiler flow will enter the TS and will settle at its temperature gradient. (with some mixing if it enters cooler than the entry point.) so if the boiler enters at 70 deg and the TS is at 60 then the boiler flow will stay at the top, heating the TS top down. If the CH or other load is taken off the top then this will take the boiler entry temp. and return the water cooler at its return point. If the flow take out of the top is greater than the boiler in flow then all will go to the load and if the load is less than the heat input then warmer water be returned. If the load more than the heat input then cooler water is returned eventually cooling the whole TS. Of course that would be theory. The dynamics of flow mixing and resistances can mess this up a bit.
If the flow take out is less than the input flow then some flow (heat) will be available to heat the TS providing the heat demand is less than the heat supply.

Typically boilers feed directly into a TS and CH is taken directly from the TS. DHW will have a heat exchanger of some sort either internal to the TS or external.

Posted By: NoodleFinally to try and limit my heating load I have been setting the store to around 65 mid to avoid heating too much water too hot and the associated extra heat loss. Would I be better off heating the top or middle up to far hotter temperature in the hope that the boiler feed/returns are hotter and the store would have a larger heat buffer and not cool down as quickly when cold heating circuits flood the store? What temp do people normally heat buffer tanks upto?

IMO you need to separate the CH and the DHW flows (It wonâ€™t matter if the returns are common) That way you will have separate control of each temp. The amount of hot water reserved for the DHW will depend upon the location of the respective flows of the CH and DHW and the temps. can be further controlled by the thermostats and the location of those thermostats.

Posted By: NoodleI do have a stat I don't currently use that temporarily stops the heating circuits if the store drops below a certain temp, maybe I should use that to allow the store to get back to a certain temp after it cools down before it starts pumping heat again?

This implies that your heat load is greater than the capacity of your boiler. E.g the CH loads exceed the boiler capacity or all CH running and then someone has a bath.
- CommentAuthorArtiglio
- CommentTimeDec 4th 2022
The system at mums runs the 4 bed house and a 1 bed annexe, 250m2 in total, all via radiators / dhwc through heat exchangers. The average pellet use over 7 years has been 8.5 tonnes, but the house has 2 wood burners and they use around 3 tonnes a year.
The annexe when it has guests gobbles huge amounts of energy, people see it as free and keep it nigh in sub tropical.
The system was designed to run with the buffer fluctuating between 60 - 80c, 40kw pellet boiler that (from memory) will modulate down to 10kw. The standing losses were huge initially but after lots of insulating of tank and pipework these were reduced by the equivalent of a tonne of pellets a year.
In winter when the heating kicks in the buffer loses temp swiftly but the boiler is able to maintain a 60c flow temp within 15 mins and bring the buffer back upto its max.
Being old mum is wedded to the old ways of heating on for a couple of hours in morning and again in evening, no end of explanation will change this unless other members of the family are there and take over the controls.
The building is traditional welsh stone, some insulation in floors and ceilings and in newer cavity walled extensions, house is epc E and annexe D. It has lots of thermal mass and once upto temperature (properly) it just ticks over comfortably, in winter the heating only really kicks in in the mornings , the wood burners keep the house warm through the day.
Let it get cold though and its a day or two to get it back up.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 4th 2022
Posted By: ArtiglioThe annexe when it has guests gobbles huge amounts of energy, people see it as free and keep it nigh in sub tropical.

All hotels I have stayed in have fixed temperatures for the rooms with no option for guests to raise (or lower) the temp. This could be done in a guest house if there was a central temp sensor in the guest house with a remote (e.g. in the boiler house) program controller.
- CommentAuthorNoodle
- CommentTimeDec 4th 2022 edited
Thanks guys. I'll take some time and have a think about all your different points.

Re guest house, yeah we have heatmiser neo stats that are locked out to guests but keep the barn at 20/21 all day basically. So fairly high heat load. I am in process of upping the insulation to the boiler room as well!

It's tough to separate our house dwh due to house with our dhw cyl in our house being fed via same burried line from barn to house.

I've got InTouch with boiler installer as he could also have left the oil boiler with the 20kw nozzle and not the 26kw one as it's a a 20- to26kw boiler depending on setup.

Bonus is I've setup a pipe stat in house house it it seems basically no heat loss on the 30m underground feed coming in at 59.9c using an stc1000 with probe on pipe under pipe insulation . The mixer in the boiler room is set to 60c.

Many thanks.
- CommentAuthorNoodle
- CommentTimeDec 4th 2022
I guess my main question then is should I super heat the top of the store to 70ish in the aim to give larger buffer or not. The idea isn't to get the entire store upto 60/70 top to bottom when not being drawn on?

Is the boiler/ energy use more or less if you have a higher kw boiler burning harder but shorter. Or a lower kw boiler burning longer but using less oil?

Or does it makes not a lot of difference and it's swings and roundabouts.
- CommentAuthorArtiglio
- CommentTimeDec 4th 2022
Peter In Hungary , yes and its how iâ€™d have it arranged , but itâ€™s another of mums foibles ( though that is born of having had so many guests over years ask ing for the heating to be on longer each day , the controller is not available to them just the thermostat). All academic now as the property is now on the market as its way past the tome she retired and downsized.
- CommentAuthorPeter_in_Hungary
- CommentTimeDec 4th 2022
Posted By: NoodleI guess my main question then is should I super heat the top of the store to 70ish in the aim to give larger buffer or not. The idea isn't to get the entire store upto 60/70 top to bottom when not being drawn on?

Is the boiler/ energy use more or less if you have a higher kw boiler burning harder but shorter. Or a lower kw boiler burning longer but using less oil?

Or does it makes not a lot of difference and it's swings and roundabouts.

Heat loss is a governed by temperature difference. The greater the difference between the TS and its surrounds the greater (faster) will be the loss. So if nothing else changes running the TS hotter will give a greater loss.

I donâ€™t think that burning the boiler at 26kW or 20kW will make any difference to the amount of oil burnt / kWh produced

You said that you were better insulating the boiler room â€“ It might be better / cheaper to better insulate the boiler, TS and the pipes. There is not much point in insulating the room if you canâ€™t make it air tight and Iâ€™m not sure that I would want a boiler room air tight.

Did your system always use as much fuel as you are using today? And have you done a detailed heat load calculation for each building? Could it be that you are using as much fuel as you are because that is the heat load of the buildings, in which case best to look at load reduction as well as increasing the efficiency of how to match the load. I see that you are a bit limited on what you can do having listed buildings but given todays fuel costs what once may have seemed not cost effective may now be back on the table.
- CommentAuthorGreenPaddy
- CommentTimeDec 5th 2022
Hi Noodle,

I might be misunderstanding your comments above, but it feels like your objective is to keep the TS hot. In reality, the TS is only there to stop short cycling. There's even less imperative to put energy into the the TS with oil, as it's better to keep the energy stored in the oil, and burn as needed.

That said, if the oil boiler is struggling to provide enough energy to keep the house&barn warm, at specific high demand times, then you may need to over charge the TS. Do you find the house/barn cooling down even when calling for heating on the UFH/rads?

Some of your observations of concern (as noted by PiH) are as I would expect the system to behave, not anything for concern, eg. the mid/lower part of the the TS cools when UFH kicks in. The boiler will have to work hard to catch up, as the initial surge of cold UFH return hits the TS, but unless the boiler doesn't manage to reheat the mid TS, then there's no issue. The cooler the TS is, in theory, the better, but that's got to be balanced with the heat load demanded from the TS.

I wonder if the return from the Barn UFH is cooler than the return from the House/Barn DHW? You could potentially connect the House return to the Barn UFH flow. I quite often link warm returns into UFH flows at the TS for various good reasons, linked to stratification. It would also help with your summer set up, as at the moment, you are still utilising the whole 1000 litres in summer, as flow and return are top and bottom of TS. If you link the House return at the mid point of the TS, you immediately halve the TS volume in use during the summer. You would also add a boiler return at the same point. Check the House return temp for a while, before considering changing anything.

Another question regards the oil boiler. Assuming it's condensing, can the boiler choose to supply hot water and CH, ie two different temperature outputs (usually there's an internal 3 port valve that diverts the flow). If so, you could set DHW to say 60oC and feed that to the top of the TS (as currently). Set CH to be say 45 or 50oC, and feed that to the mid TS. They are each triggered by a stat at the two respective locations on the TS. That means the boiler will tend to supply water at a lower temp to the UFH for the barn at a lower temp, which is adequate for the Barn UFH, but much more efficient from a boiler condensing view point. This could be tapped in at the UFH flow connection on the TS, if that's easier than a new direct TS connection.

I've attached a quick sketch of the above. Note, my points are based upon a few written messages, interpretation, and assumption - not a detailed analysis. So take these as pointers, that need further investigation. Also, these won't give huge savings, maybe 10%ish if lucky. The key issue is high energy consumption.

It's a shame pellet boilers were such a flop, as people (and the tax payer) have lost out financially and had endless inconvenience.
- Noodle System.pdf
- CommentAuthorNoodle
- CommentTimeDec 5th 2022 edited
Posted By: Peter_in_Hungarycheaper to better insulate the boiler, TS and the pipes.

yep ive just finished insulating all the pipework... the boiler room had most of it missing before... also insulated the store more but not sure about insulating the oil boiler? perhaps a insulated box with 50mm gap and some ventilation holes?

Posted By: Peter_in_HungaryDid your system always use as much fuel as you are using today? And have you done a detailed heat load calculation for each building? Could it be that you are using as much fuel as you are because that is the heat load of the buildings,

yep, always has so I know our heat load is high but just trying to optimize it and was concerned over long burn times. boiler on times. not a lot more we can do energy efficiency wise.

Posted By: GreenPaddyDo you find the house/barn cooling down even when calling for heating on the UFH/rads?

thanks for all your thoughts, its helped solidify mine. No the store has always had enough heat and has worked, our buildings are toasty. The barn ufh takes hours to heat the space but I think that was a crap install from the contractor and flooring is stuck down using ribbons of glue and so big air pockets everywhere...

I think generally the store is working correctly and return temps from heating circuits are fine and to be expected. I have decided thou that the store would work more efficiently with the oil boiler with the stat staying in the top pocket at 65C. This provides ample CH water and calls for heat when the barn UFH takeoff gets down to about 50C which is still ample for the UFH ( mixed to 40C at the manifold). This means im only heating top 1/3 of the store to 65C and not 1/2 of it which will hopefully be more fuel efficient.

My remaining query was the actual Vortex oil boiler feed and return, I have the boiler set to max temp but when the bottom of the store is 45C the boiler feed seems to only be reaching 65C, struggling to heat the feed temp higher I guess. I've asked the installer what KW rating they set the oil boiler to, it might only have the 20kw nozzle, not 26kw. I mean im only using an stc1000 with temp probe silver foil stuck to the pipe under insulation, so not sure how accurate that is!

Thanks for everyone's thoughts and ideas.

Posted By: GreenPaddyI've attached a quick sketch of the above

cheers for your ideas, will have to look into boiler options and if possible!

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