Underfloor with condensing oil boiler

gooner99

Anyone experience of running or installing underfloor run by a condensing oil boiler in an A rated house with a high level of insulation (e.g. 200mm cavity with bonded bead), airtightness and mvhr. I understand a2w is more suited to underfloor but unfortunately it's an expensive piece of kit on an exposed site where everything is rusted with sea salt. It wouldn't last long enough to pay back the investment. My thinking is that in a house like this with a low heat demand the running costs should be low.

Tom44

Why not ?


Condensing oil boilers running underfloor heating is very common.
An energy efficient house simply means your also not loosing that heat easily to the outside.
Talk to your local contractor.
Just DON'T oversize boiler.
It's not a big deal, and pound for pound, makes sense.
Do the calculations, well, your contractor should do that.

Has the house been built yet ?

gooner99

Tom44 wrote: »

Why not ?


Condensing oil boilers running underfloor heating is very common.
An energy efficient house simply means your also not loosing that heat easily to the outside.
Talk to your local contractor.
Just DON'T oversize boiler.
It's not a big deal, and pound for pound, makes sense.
Do the calculations, well, your contractor should do that.

Has the house been built yet ?

No not started. I plan to wire for PV, for future installation.

Tom44

gooner99 wrote: »

No not started. I plan to wire for PV, for future installation.

Good idea.

Its very easy and cheap to pipe for all alternatives on a new build.
It keeps all options open, for now or in the future.
Even if never utilized.

gooner99

Have you experience of oil and underfloor Tom?

Tom44

gooner99 wrote: »

Have you experience of oil and underfloor Tom?

We all have here.
Your talking to a good panel of experience professionals here with wide experience.

gooner99

Tom44 wrote: »

We all have here.
Your talking to a good panel of experience professionals here with wide experience.

Thanks Tom. Any opinions of running costs in a low energy house?

Tom44

gooner99 wrote: »

Thanks Tom. Any opinions of running costs in a low energy house?

How long is a piece of string.?


Depends on size of house and what hours of usage + volume of hot water required.
No two houses and families are the same.

But forget all that.
Basically a good system with a condensing (GRANT) boiler will be extremely efficient compared to an old house with a bad system.

Jakey Rolling

As mentioned, don't oversize your condensing boiler.
The DEAP calculation for your BER should indicate the heat losses for the build and your should size the boiler accordingly.

We have been in our house 5 years, nominal A3 BER - 320m2, UFH, 150mm bead cavity, MHRV, solar thermal.

A 35kW Grant oil boiler was installed at plumbers recommendation.
Boiler keeps the UFH topped up, and will heat the water tank to 50C in morning or evening if required (rarely, as solar is effective March-November)
The BER done on completion gave the heat loss at around 15kW.
I noted that the boiler seemed to be cycling excessively (over 20 start/stops per hour), so at the last service we changed the nozzle to bring the boiler down to minimum setting of 26kW, will see if that makes any difference this winter.


FYI, our average usage over the last 5 years has been 1200 litres oil p.a., so about 12000kWh.
Adding in electricity usage of 5200kWh, the energy use has been 53kWh/m2 over that period (about 71kWh/m2 BER figure once the electricity loading factor is applied). So just makes it into the A3 band as-built performance.

Wearb

Good info there Jake.
The size of your boiler instantly jumped out at me. With well zoned heating it should be possible to go a lot lower. Down rating to 26Kw will be a big help. That along with being able to continuously run it in condensing mode should bring down your usage a little.

I am curious as to why its cycling so much (even with an oversized boiler). With that ber, it should take a while for your return to get cold enough to fire the boiler. Ask your plumber next time if the boiler is properly interlocked. Do you have a buffer tank?

Jakey Rolling

Wearb wrote:

I am curious as to why its cycling so much (even with an oversized boiler). With that ber, it should take a while for your return to get cold enough to fire the boiler. Ask your plumber next time if the boiler is properly interlocked. Do you have a buffer tank?

No buffer tank. Fully zoned and with weather compensation sensor.

My impression is that once the slab is up to temperature in October the heat demand is very low - my calcs were about 5kW per 10deg temp difference to the outside. So the boiler is blasting out 35kW, mixed down to about 35 degree flow temp. Haven't seen flow temp go above 40. I'd say the return is always sufficiently low to fire the boiler. The thermal mass of the block walls also has a buffering effect, internal air temperature is very stable. (The oil was cut off in April last year and it took us 2 days to notice).

I'd love to try a 16kW boiler to see how it performs! TBH a modulating gas boiler would have been my choice if we had mains gas.

Wearb

Jakey Rolling wrote: »

No buffer tank. Fully zoned and with weather compensation sensor.

My impression is that once the slab is up to temperature in October the heat demand is very low - my calcs were about 5kW per 10deg temp difference to the outside. So the boiler is blasting out 35kW, mixed down to about 35 degree flow temp. Haven't seen flow temp go above 40. I'd say the return is always sufficiently low to fire the boiler. The thermal mass of the block walls also has a buffering effect, internal air temperature is very stable. (The oil was cut off in April last year and it took us 2 days to notice).

I'd love to try a 16kW boiler to see how it performs! TBH a modulating gas boiler would have been my choice if we had mains gas.

I am not sure that weather compensation works very well with your setup. As you already discovered, it has a slow reaction time.
Modern insulation/airtightness c/w underfloor and heat recovery, do give a very stable comfortable temperature.

It would be great to be able to modulate right down to what's required. Maybe on you next boiler change

gooner99

Thanks for the replies and advice so far. Also good to hear positive first hand experience.

My house will be 150sqm story and half. Lots of south/west triple glazing. Insulation u value spec is around 0.15 for floor wall and roof. 200mm pumped cavity, so good thermal mass in the walls. I figure this along with good airtightness and mvhr in this compactly sized house the heat demand will be sufficiently low as to favour a cheaper correctly sized oil condensing boiler and underfloor setup as opposed to a2w. Hard to see the payback with a2w in this case, while also taking into account the salt air which would likely destroy the outdoor unit long before even the normal payback period. Just my thoughts on it?

Gas also sounds like an option, but it probably only makes sense if on mains supply?

What would the current optimum oil and underfloor setup be?

Tom44

I service lots of oil boiler's on the coast, literally.
Some over 30 years old and within 100m of the water, haven't noticed any salt effect problems yet.
But I've only been doing it for over 20 years now, so time will tell.


But my experience is only with oil, as that's my trade. Service & Repairs
In my previous misguided sad life I was a plumbing & heating contractor, before I saw the light.
Others will have better knowledge on other systems, that's the benefit of BOARDS

gooner99

Tom44 wrote: »

I service lots of oil boiler's on the coast, literally.
Some over 30 years old and within 100m of the water, haven't noticed any salt effect problems yet.
But I've only been doing it for over 20 years now, so time will tell.


But my experience is only with oil, as that's my trade. Service & Repairs
In my previous misguided sad life I was a plumbing & heating contractor, before I saw the light.
Others will have better knowledge on other systems, that's the benefit of BOARDS

I'm right on the sea front and the internal metal parts on the pvc window openings of my current house are rusted, even on the ones that are rarely opened. I'd imagine an a2w unit sucking in salt laden air may be different to an outdoor oil boiler. I could be wrong though?

gooner99

Jakey Rolling wrote: »

As mentioned, don't oversize your condensing boiler.
The DEAP calculation for your BER should indicate the heat losses for the build and your should size the boiler accordingly.

We have been in our house 5 years, nominal A3 BER - 320m2, UFH, 150mm bead cavity, MHRV, solar thermal.

A 35kW Grant oil boiler was installed at plumbers recommendation.
Boiler keeps the UFH topped up, and will heat the water tank to 50C in morning or evening if required (rarely, as solar is effective March-November)
The BER done on completion gave the heat loss at around 15kW.
I noted that the boiler seemed to be cycling excessively (over 20 start/stops per hour), so at the last service we changed the nozzle to bring the boiler down to minimum setting of 26kW, will see if that makes any difference this winter.


FYI, our average usage over the last 5 years has been 1200 litres oil p.a., so about 12000kWh.
Adding in electricity usage of 5200kWh, the energy use has been 53kWh/m2 over that period (about 71kWh/m2 BER figure once the electricity loading factor is applied). So just makes it into the A3 band as-built performance.

How did you get on with the new boiler setup during this heating season?

Jakey Rolling

gooner99 wrote: »

How did you get on with the new boiler setup during this heating season?

Appears to have made very little difference to the cycle time of the boiler, I'd still say it's oversized at 26kw.

Even at the time I would have gone for a modulating gas boiler, but natural gas wasn't an option and bulk Calor tank appeared to work out more expensive than oil.

John.G

Wearb wrote: »

Good info there Jake.
The size of your boiler instantly jumped out at me. With well zoned heating it should be possible to go a lot lower. Down rating to 26Kw will be a big help. That along with being able to continuously run it in condensing mode should bring down your usage a little.

I am curious as to why its cycling so much (even with an oversized boiler). With that ber, it should take a while for your return to get cold enough to fire the boiler. Ask your plumber next time if the boiler is properly interlocked. Do you have a buffer tank?

Distant relation very recently brought up the issue of excess cycling with his 26 KW HE oil boiler and UFH especially if his heat demand goes down to ~ 5KW, I was thinking that with mixing valve(s) to reduce the boiler flow temperature from 65C to 45C and with a return temperature of 40C that there would only be a very small flow rate through the boiler and therefore a very rapid rise in boiler temperature and consequent quick boiler run times. My thinking is that with those sort of temperatures that the ratio of the mixed flow rate to the Boiler flow rate would be in the order of 5:1 so a heat demand of ~ 5 KW and UFH Delta T of 5C would require a UFH flow rate of ~ 14 LPM but a boiler flow rate of only 2.8 LPM if this is how the mixing system works?.

anthonyos

Always a good idea to fit a system link or a low loss header with underfloor its the only way it works correctly

DGOBS

Would you not consider either a heat pump, or is you load is too big, then a hybrid unit (Like grants)

gctest50

Jakey Rolling wrote: »

Appears to have made very little difference to the cycle time of the boiler, I'd still say it's oversized at 26kw.

Even at the time I would have gone for a modulating gas boiler, but natural gas wasn't an option and bulk Calor tank appeared to work out more expensive than oil.

A big accumulator tank will give it sonething to do and stop it cycling like crazy

John.G

gctest50 wrote: »

A big accumulator tank will give it sonething to do and stop it cycling like crazy

Oil fired boilers seem well able to handle constant cycling, much the same can happen when the hot water zone only is open which can happen for the whole summer season if hot water demand justifies running the boiler vs electric immersion for very small volumes. Don't know if anyone has ever worked out the efficiency loss due to frequent cycling but it may not be huge.
If it were my system above I would certainly consider fitting a pipe stat (with adjustable differential) to the boiler flow set at say 45C closing temperature or slightly higher wired in series with the existing boiler stat (&hi limit stat), or replace the boiler stat with a digital stat which has a adjustable differential, this might achieve two things, an much increased flow through the boiler as the mixing valve closes in and also a increased "store" as at 45C the boiler is circulating all the water around the system, this may have a significant effect on the cycling time without costing a fortune to implement/try out.

Wearb

John.G wrote: »

Oil fired boilers seem well able to handle constant cycling, much the same can happen when the hot water zone only is open which can happen for the whole summer season if hot water demand justifies running the boiler vs electric immersion for very small volumes. Don't know if anyone has ever worked out the efficiency loss due to frequent cycling but it may not be huge.
If it were my system above I would certainly consider fitting a pipe stat (with adjustable differential) to the boiler flow set at say 45C closing temperature or slightly higher wired in series with the existing boiler stat (&hi limit stat), or replace the boiler stat with a digital stat which has a adjustable differential, this might achieve two things, an much increased flow through the boiler as the mixing valve closes in and also a increased "store" as at 45C the boiler is circulating all the water around the system, this may have a significant effect on the cycling time without costing a fortune to implement/try out.

I haven’t time to consider and respond to all the above, but someone posted the results of a cycling study on gas boilers some time back here. It was a lot of reading but bottom line was that it wasn’t nearly as wasteful as previously thought.
I could search for it sometime if you are interested.

Wearb

Wearb wrote: »

I haven’t time to consider and respond to all the above, but someone posted the results of a cycling study on gas boilers some time back here. It was a lot of reading but bottom line was that it wasn’t nearly as wasteful as previously thought.
I could search for it sometime if you are interested.

You might be familiar with this thread already.


See post #22 for link

https://www.boards.ie/vbulletin/showthread.php?p=99005357


I just checked the link. It's only partially working. If you are interested, I will see if I have saved this to my pc?

John.G

Wearb wrote: »

I haven’t time to consider and respond to all the above, but someone posted the results of a cycling study on gas boilers some time back here. It was a lot of reading but bottom line was that it wasn’t nearly as wasteful as previously thought.
I could search for it sometime if you are interested.

I found this in my "archives".....don,t know if it relates to oil or gas boilers, gas boilers do a post purge I think but oil fired do not) so it would appear that a boiler cycling 20 times per hour like gooner99 above might incur a ~ 3% loss based on his cycle time of (3600/20) 180 secs, and assuming that half of the cycle, 90 secs, is the "operational time per cycle"

Table 3 Percentage energy loss based on boiler purge time
Operational time per
cycle (seconds) Base efficiency % % loss Gross
3600 85.9% 0.0%
180 84.4% -1.5%
120 83.6% -2.3%
60 81.8% -4.1%
30 79.1% -6.8%
10 74.1% -11.8%

Wearb

John.G wrote: »

I found this in my "archives".....don,t know if it relates to oil or gas boilers, gas boilers do a post purge I think but oil fired do not) so it would appear that a boiler cycling 20 times per hour like gooner99 above might incur a ~ 3% loss based on his cycle time of (3600/20) 180 secs, and assuming that half of the cycle, 90 secs, is the "operational time per cycle"

Table 3 Percentage energy loss based on boiler purge time
Operational time per
cycle (seconds) Base efficiency % % loss Gross
3600 85.9% 0.0%
180 84.4% -1.5%
120 83.6% -2.3%
60 81.8% -4.1%
30 79.1% -6.8%
10 74.1% -11.8%

Interesting results and from my (poor) memory are close to what I read.

Firebird have a digital box with post purge. I don’t know if they’re fitted to Irish market boilers. However the post purge would produce greater losses than pre purge. On those boilers it would be more desirable to reduce short cycling.

jimf

Wearb wrote: »

Interesting results and from my (poor) memory are close to what I read.

Firebird have a digital box with post purge. I don’t know if they’re fitted to Irish market boilers. However the post purge would produce greater losses than pre purge. On those boilers it would be more desirable to reduce short cycling.

firebird had them on their old riello burner but afaik these were only on the boilers for the uk market could be wrong but never came across the digi box here


they now have it on the elco low nox burner for all markets hence the need for a permanent live to all boilers

Wearb

I saw one of them a few years back. I wasn’t working on it and can’t remember where.

relayman

gooner99 wrote: »

Anyone experience of running or installing underfloor run by a condensing oil boiler in an A rated house with a high level of insulation (e.g. 200mm cavity with bonded bead), airtightness and mvhr. I understand a2w is more suited to underfloor but unfortunately it's an expensive piece of kit on an exposed site where everything is rusted with sea salt. It wouldn't last long enough to pay back the investment. My thinking is that in a house like this with a low heat demand the running costs should be low.

Hello.
I am in the process of building an extension 1000 square feet.My plumber recommended on putting under floor heating instead of rads in extention. He recommended a 26Kw condensed grant oil boiler. It will be heating a total of 2500 square feet altogether 1500 on rads. How have you found this system since install did you get the boiler sorted from starting stopping? Thanks in advance.

SusanY

we are looking at buying a bungalow 1800 sq ft with oil fired underfloor heating, it’s has a BER of B3. Would this be expensive to run or might it be better to upgrade to a heat pump? Just not sure if the expense & work involved would be viable! Has anyone any experience of this? Many thanks

Sleeper12

https://www.boards.ie/discussion/comment/122137948#Comment_122137948

A heat pump won't be cheap to run on a B3 home. Government won't tell you but you need an A rating for low cost energy from a heat pump. A heat pump will heat up a B3 but not cheaply. Gas or oil will be far cheaper at this rating