Duoheat combines storage heater & panel heater. The idea being whilst the storage heater may be cool at 8pm (40oC), there is still stored energy so the full-front thin film heater need only increase that by 20oC to get the temperature delta high enough for usable heating (60oC).
This notwithstanding the conservation of energy applies.
Thus there is no real difference over a conventional storage heater with a physically separate panel heater?
I ask because Duoheat involves electronics of undoubtedly less than
25yr reliability, conventional involves a capillary tube of 25yr reliability. Duoheat controller does simplify usage re Comfort- Background-Frost-Off at the addition of another area of failure & pilot wire/mains borne signalling. Buying spares re heater PCB, thin- film heater, controller is not a problem. Duoheat is much more popular and sells fast & high on Ebay, but that may just be BuyToLet crowd.Just for any physics bods out there :-)