Duoheat vs Conventional

jason1959

My mother has one 3.3kW E7 in the hall (24kW), could do with another after winter 2008. Elsewhere gas fires, not interested in GCH or warmup (solid floors down, partly up, differing ceiling & floor levels) and prefers the stable temperature of E7. Other similar houses have ironically ditched GCH at boiler failure re depreciation, powerflush maintenance costs together with pig ugly surface piping. Loft & CWI, south facing which makes a surprising difference.
Option-1 - Duoheat 500 & 400.
- E7 = 2.55+1.95 x7 = 31.6kW (stored)
- Peak = 0.40+0.35 x 12 = 9kW (panel).
- Total per day at 100% = 40.5kW
- Combined cost per kW = 6.6p
Option-2 - Conventional 3.3 & 2.55kW
- E7 = 3.3+2.55 x7 = 41kW (stored)
- Total per day at 100% = 41.0kW
- Combined cost per kW = 5.0p
Option-3 Conventional 3.3 & 2.55kW + 0.7kW panel
- E7 = 3.3+2.55 x7 = 41kW (stored)
- Peak = 0.70 x 12 = 8.4kW (panel).
- Total per day at 100% = 49.4kW
- Combined cost per kW = 6.2p

Duoheat?
- Pretty.
- Complex Controls (programmer may solve if Comfort - Background - Off!).
- Integral panel heater.
- Unknown *electronics* reliability (requires spare parts re obsolescence risk).
Conventional?
- Ugly
- Idiot proof controls.
- No integral panel heater (even uglier).
- Proven 25yr reliability (*capillary tube* charge controller).

Using Ebay as a guide, people can't give away conventional - yet buy Duoheat like they are going out of fashion. That might just be BTL avoiding gas (and I can't blame them having done livetime cost of neighbours). Alternatively it may be they really DO solve the "too hot overnight, too cold at 8pm".

2 questions...
#1 - Reliability of Duoheat
Reliability of electronic controller, thin film panel?
#2 - Physics of Duoheat using a panel boost
When a storage heater appears "cold" at say 40oC it still has energy, so the internal panel heater only has to boost the temperature by 20oC to get it back up to 60oC. That might be more *comfort efficient* than using a separate heater - or it may make no difference at all (conservation of energy applies :-)
Anyone owned BOTH conventional storage heater (perhaps with SEPARATE boost late evening heater) AND Duoheat?

Not asking much am I, however I'm paying so I'd rather not get it wrong. For Duoheat I would obviously buy spares at the outside (they are not much if you shop around re panel, control PCB, charge PCB, 2 elements).
As you can see cost is minor - gas fires total 8000kW per year, E7 2500-3500kW per year re dryer/heating and peak is 3200kW per year cooker/dryer.

As yet ASHP are not quite under permitted development re noise regs (a pity although frankly it's added complexity - I want rock solid reliability).

Fire_Fox

What is it you actually want to know, your post reads like a physics lesson.

jason1959

Q #1 - Anyone experienced any reliability issues with Duoheat?
(ie, any failures of electronics or thin-film on-peak heater panel, both of which can be less reliable than conventional non-electronic storage heaters).

Q #2 - Anyone having owned BOTH conventional storage heater AND Duoheat able to report on their experience?


As to physics, well that question is soon resolved.
I was curious to know whether a Duoheat (E7 + peak-panel) by having an internal peak-boost panel heater would thermally outperform a conventional storage heater (E7 only) with physically separate panel heater (peak).
The answer is there is no difference due to conservation of energy.
Duoheat does however deliver more convenience & control (E7 + peak-panel heater in same box), what I want to know is whether the price is electronic reliability.