Thermal store or hot water cylinder

Vegfarmer

Member
Horticulture
Hi all,
I'm own a wood stove boiler, 12kw to water, the old oil boiler needs replacing also. In the future solar panels may be fitted for summer time. Ideally have new oil boiler within circuit for occasions when fires isn't going but may cope without and just have stove & solar.
Wondered which would suit better a thermal store or hot water cylinder?
It would need to do about 10 radiators and supply hot water for taps.
Hetas heating engineer is coming out to do quote/design but which would be most efficient also simple and less cost. Advice appreciated.
Many thanks
 

br jones

Member
Hi all,
I'm own a wood stove boiler, 12kw to water, the old oil boiler needs replacing also. In the future solar panels may be fitted for summer time. Ideally have new oil boiler within circuit for occasions when fires isn't going but may cope without and just have stove & solar.
Wondered which would suit better a thermal store or hot water cylinder?
It would need to do about 10 radiators and supply hot water for taps.
Hetas heating engineer is coming out to do quote/design but which would be most efficient also simple and less cost. Advice appreciated.
Many thanks
solar thermal is better for water heating,unless battery accompany the solar panels
 

steveR

Member
Mixed Farmer
Hi all,
I'm own a wood stove boiler, 12kw to water, the old oil boiler needs replacing also. In the future solar panels may be fitted for summer time. Ideally have new oil boiler within circuit for occasions when fires isn't going but may cope without and just have stove & solar.
Wondered which would suit better a thermal store or hot water cylinder?
It would need to do about 10 radiators and supply hot water for taps.
Hetas heating engineer is coming out to do quote/design but which would be most efficient also simple and less cost. Advice appreciated.
Many thanks
Surely the flexibility of a big ass thermal store will be the best long term and future proof option for you?

Spec it so you can top it up from just about any heat source then... Solar thermal, PV via internal immersion heater and your wood boiler. Then use the hot water, as you like.
 

renewablejohn

Member
Location
lancs
Dont expect miracles from a Hetas engineer. If you want real advice go to a heating engineer who can actually design an integrated heating system which can use a range of heating sources such as biomass, solar, gas, oil and understands the difference between a thermal store and a hot water cylinder. Your Hetas engineer is just an installer of biomass systems.
 

e3120

Member
Mixed Farmer
Location
Northumberland
Surely the flexibility of a big ass thermal store will be the best long term and future proof option for you?

Spec it so you can top it up from just about any heat source then... Solar thermal, PV via internal immersion heater and your wood boiler. Then use the hot water, as you like.
Completely agree. Flexibility of how you heat it, and not committed to end use (ch or dhw) at that point in time. Also provides convenient neutral point.

Of course my one is not big enough, but I get most of the benefits of a larger size by an intelligently plumbed/switched cheap polish buffer tank alongside.
 

steveR

Member
Mixed Farmer
Completely agree. Flexibility of how you heat it, and not committed to end use (ch or dhw) at that point in time. Also provides convenient neutral point.

Of course my one is not big enough, but I get most of the benefits of a larger size by an intelligently plumbed/switched cheap polish buffer tank alongside.
The heat store here is 300l and is too small. I said so at the time it was installed, and time has proven me correct, I am sorry to say...

With only two of here now for most of the time nowadays, it does not warrant the cost of an additional or replacement tank.
 

Runs Like a Deere

Member
Mixed Farmer
I have a thermal store that is heated with oil boiler and wood burning stove, great bit of kit, I think mine is 500L and runs 11 rads at the moment. Only thing I wish I could control a bit better is when the central heating pump kicks in I feel it doesn't come in soon enough when the stove is running but I am not a heating engineer so maybe there is a reason for it. It has an immersion element too so i could go electric only if I lost my mind but I never will.

I am not sure how many inputs you can get on on them, I think mine only has two which is perfect for now but obviously I don't have capacity to include solar panels if I had them. I think they can be made to order however and probably with another heat exchanger input.
 

steveR

Member
Mixed Farmer
I have a thermal store that is heated with oil boiler and wood burning stove, great bit of kit, I think mine is 500L and runs 11 rads at the moment. Only thing I wish I could control a bit better is when the central heating pump kicks in I feel it doesn't come in soon enough when the stove is running but I am not a heating engineer so maybe there is a reason for it. It has an immersion element too so i could go electric only if I lost my mind but I never will.

I am not sure how many inputs you can get on on them, I think mine only has two which is perfect for now but obviously I don't have capacity to include solar panels if I had them. I think they can be made to order however and probably with another heat exchanger input.
You could use Solar PV, by diverting any surplus (or all) power to the immersion heater if wanted... Say in summertime when the wood stove is off?

Or possibly, solar thermal instead of the woodburner, using the same heat exchanger? Simple valve changeover?
 

Runs Like a Deere

Member
Mixed Farmer
You could use Solar PV, by diverting any surplus (or all) power to the immersion heater if wanted... Say in summertime when the wood stove is off?

Or possibly, solar thermal instead of the woodburner, using the same heat exchanger? Simple valve changeover?

Yeah I am sure there would be a simple option to include solar panels but currently a moot point as I don't have any at the moment. would be interesting to see if they could be manifolded together so you don't need to have valve to switch they both just feed into the tank?
 

Kidds

Member
Horticulture
Hi all,
I'm own a wood stove boiler, 12kw to water, the old oil boiler needs replacing also. In the future solar panels may be fitted for summer time. Ideally have new oil boiler within circuit for occasions when fires isn't going but may cope without and just have stove & solar.
Wondered which would suit better a thermal store or hot water cylinder?
It would need to do about 10 radiators and supply hot water for taps.
Hetas heating engineer is coming out to do quote/design but which would be most efficient also simple and less cost. Advice appreciated.
Many thanks
I don't rate my thermal store much, shower goes cold too quick and not enough hot water for a bath if the pumps have kicked in. Hot water tank in old place was much better.
If the pumps haven't come on (heat and/or DHW) there is plenty of hot water.
 
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steveR

Member
Mixed Farmer
I don't rate my thermal store much, shower goes cold too quick and not enough hot water for a bath if the pumps have kicked in. Hot water tank in old place was much better.
If the pumps haven't come on (heat and/or DHW) there is plenty of hot water.
Temp Settings too low on the thermostat?

I was told not to run the bath too fast when filling from our store (with a pump) as it caused mixing as opposed from pulling off the top slowly.

Our biggest issue is that the towel rails are heated from the same hot water and they pull the DHW temp down far too much this time of year.
 

steveR

Member
Mixed Farmer
Yeah I am sure there would be a simple option to include solar panels but currently a moot point as I don't have any at the moment. would be interesting to see if they could be manifolded together so you don't need to have valve to switch they both just feed into the tank?
Some thermal stores will have several heat exchange coils, so you can have inputs from several sources, asopposed to manifolds as you describe.... that sounds problematic.
 

curlietailz

Member
Arable Farmer
Location
Sedgefield
Some thermal stores will have several heat exchange coils, so you can have inputs from several sources, asopposed to manifolds as you describe.... that sounds problematic.

mine is 800 litres thermal store and has at least two heating options

currently only heated by biomass boiler and then through the a plate exchanger into the house radiators

looking to add the solar panels through Emmerson heater as a second source as I have a Immersun fitted to the 8kw solar array to divert unused electric to the hot water cylinder atm but that’s a waste of the spare electric imho

I’m also looking at replacing the existing wood burning stove with a wood burner with back boiler to heat 3 or 4 extra radiators …

in an old farmhouse I feel there is a need for multiple back up plans
 

Gareth J

Member
Mixed Farmer
You ought to separate DHW from space heating; DHW needs to be hotter, is needed all year round and available most of the day. It's impractical to store a whole big (which you'll benefit from with quite a big wood boiler) thermal store at DHW temps all the time.

You could do this with a relatively tall thin tank and use stratification to keep the top hotter, or separate DHW from heating water with a separate, small, DHW tank in the house and a bigger thermal store somewhere more practical.
 

steveR

Member
Mixed Farmer
mine is 800 litres thermal store and has at least two heating options

currently only heated by biomass boiler and then through the a plate exchanger into the house radiators

looking to add the solar panels through Emmerson heater as a second source as I have a Immersun fitted to the 8kw solar array to divert unused electric to the hot water cylinder atm but that’s a waste of the spare electric imho

I’m also looking at replacing the existing wood burning stove with a wood burner with back boiler to heat 3 or 4 extra radiators …

in an old farmhouse I feel there is a need for multiple back up plans
Mine has in effect, 3 options.

GSHP Output
PV into immersion coil
Spare Ports for Solar thermal, or other heat source. The latter is what I am looking at for emergency heating by an LPG boiler.
 

steveR

Member
Mixed Farmer
You ought to separate DHW from space heating; DHW needs to be hotter, is needed all year round and available most of the day. It's impractical to store a whole big (which you'll benefit from with quite a big wood boiler) thermal store at DHW temps all the time.

You could do this with a relatively tall thin tank and use stratification to keep the top hotter, or separate DHW from heating water with a separate, small, DHW tank in the house and a bigger thermal store somewhere more practical.
I genuinely think that this is an excellent idea. Although in our case the CH supply comes direct from a buffer tank and the GSHP. I want the separate hot water for the towel rail circuit... also a year round requirement!
 

Vegfarmer

Member
Horticulture
Thanks for the replies! Looking into the right size thermal store, and will be involving Local firm who seem knowledgeable. The boiler stove i have has 13.6 kw output to water. The other inputs would be solar in the future and maybe oil boiler as back up. About 12 radiators plus hot water but main use is heating.
Store would be directly above stove in house. Thought 350 L as didn't want to oversize it so the stove & heating might struggle. Has anyone else had this?
 

Gareth J

Member
Mixed Farmer
Thanks for the replies! Looking into the right size thermal store, and will be involving Local firm who seem knowledgeable. The boiler stove i have has 13.6 kw output to water. The other inputs would be solar in the future and maybe oil boiler as back up. About 12 radiators plus hot water but main use is heating.
Store would be directly above stove in house. Thought 350 L as didn't want to oversize it so the stove & heating might struggle. Has anyone else had this?

A 13kw stove, (losses aside) would heat a 350l store from 30C to 80C in under two hours.

12 rads (total ~30kw?) Will drain the same store from 80 to 30 in less than 45mins

Have a play here, or somewhere similar;

It depends on what you want to achieve. Some people with a relatively big wood boiler, yours is bigger than a lot, want to be able to fire it at a convenient time, say when they're out and about in the day but don't necessarily need the heating on, then enjoy the heating in the evening/next morning. To achieve that, you'd need a much bigger store. Like 1000+litres. Usually in an outbuilding somewhere.

If you're limited to the space that's available in whatever cupboard is directly above the stove (weight on the floor too?) Then it'll have to be what it it'll be.

Assuming the store contains shared water that flows around both the boiler/s and rads and has a HX to get heat into the tapwater? You can do it differently but that seems to me to be simplest. For comparison, I have a 450l stove with a built-in coil for DHW, the coil is less effective at getting the heat out the store and into tapwater than a plate HX and pump but there's les to buy and maintain. Wouldn't want a smaller coil in a smaller body of water (sits in the top half of the tank, say 250l) it can run a very nice shower on its own or two ok ones. Probably not appropriate for a big family.

Don't worry too much about oversizing, you can put an "economy" stat in the top of the tank so that, in summer, you're only keeping a smaller top portion of the store hot for tapwater with the boiler and, if you fit solar, a bigger tank will help buffer duller days.
 

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