Use a twin coil unvented cylinder with boiler only

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Hi all,

I have a query about a twin coil solar cylinder. I’ve seen some information online that it can be more efficient and lead to faster reheat times to use both coils with a single boiler.



Has anyone experience with this or not? I’m asking as I can get a great deal on twin coil OSO Delta (A rated) so it might be an option.

I’m sure I’ll be told it’s a load of **** but thought I’d ask.

Thanks for all your help to date.
 
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Yes we have installed several twin coils like that when 'future proofing ' a system.
You do get noticeably quicker re heat exactly what you would expect.
That’s great to hear. Would you install them in parallel or in sequence?
Any experience with the OSO delta twin coil?
Thanks
 
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Have linked coils together on some jobs made them separately controlled on others
Depends what customer wants.
Thanks for this. What would you say is best. I’m assuming having all part of the same ‘heat up’ system (i.e. not having it programmed separately) is the most straight forward? Would that be your preference? Thanks
 
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Due to type of property's we normally work in usually have bespoke cylinders made so you can create your own specification.
High performance coils increased insulation ect.
Mostly because there fairly close and I can collect we use Newark Cylinders .
 
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Thanks for this. What would you say is best. I’m assuming having all part of the same ‘heat up’ system (i.e. not having it programmed separately) is the most straight forward? Would that be your preference? Thanks
You should get, with 3 or 4 lever valves and one motorized valve, bottom coil only, top coil only and bottom and top coil in series (at least), may need two cylinder stats with c/o switch but looks doable?
 
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I have a 300l Tempest Solar, linked the output from top coil to input of bottom coil which was the direct instruction of manufacturer. If you contact manufacturer they might tell you best option for your tank.
 
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I have a 300l Tempest Solar, linked the output from top coil to input of bottom coil which was the direct instruction of manufacturer. If you contact manufacturer they might tell you best option for your tank.
Great stuff. Have you found (well I guess you can’t compare to what it was before) that it works well? I think the extra coil means you have the option of adding solar thermal if indeed it became viable. But in the meantime getting the faster heat time
 
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Great stuff. Have you found (well I guess you can’t compare to what it was before) that it works well? I think the extra coil means you have the option of adding solar thermal if indeed it became viable. But in the meantime getting the faster heat time
I tried to have solar thermal fitted to my flat garage roof but nobody was interested. If you don't link the coils only half the tank heats up, so in that respect it made the tank much more useful!
 
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I tried to have solar thermal fitted to my flat garage roof but nobody was interested. If you don't link the coils only half the tank heats up, so in that respect it made the tank much more useful!
Yeah I think how the solar works is the bottom coil is for Solar and the top one is for boiler (or other source). The bottom coil is usually bigger. Some setups have timers on only heating the upper coil during the day and both coils in the morning/evening when there is more demand. However, if you get an A rated cylinder (like an OSO Delta) you only lose 3 degrees over 24 hours so not sure it’s worth going to that level of effort!
Sorry to hear you couldn’t get the solar thermal
Installed. People seem to be offering it still though.
Did you have any issues with air locking. Should you put a vent on the lower coil?
 
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Yeah I think how the solar works is the bottom coil is for Solar and the top one is for boiler (or other source). The bottom coil is usually bigger. Some setups have timers on only heating the upper coil during the day and both coils in the morning/evening when there is more demand. However, if you get an A rated cylinder (like an OSO Delta) you only lose 3 degrees over 24 hours so not sure it’s worth going to that level of effort!
Sorry to hear you couldn’t get the solar thermal
Installed. People seem to be offering it still though.
Did you have any issues with air locking. Should you put a vent on the lower coil?
I can't see why there would be any issue, but then I'm not a plumber, just an enthusiastic DIYer. By connecting the two you're essentially making one large coil, so no issues I can think off. I heat my tank twice a day and also have a hot water recirculating pump to get water to far away taps quicker; hot water costs pennies compared to heating, especially with an efficient tank!
 
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