Can a dehumidifier reducing household energy consumption? Debunk this claim I have recently bought a dehumidifier to control humidity in the winter, prevent mould and stop windows steaming up.
Claims of reduced heating cost
I noticed when looking what to buy, that some claim the reduced humidity in the air can reduce your heating bill. I very much doubt this, given that the humidifier costs money to run. There seems to be a lot of myths from misunderstanding of thermodynamics and humidity.

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*"Cheaper heating bills – because the dehumidifier removes the moisture from the air in your home" (https://blog.meaco.com/how-much-does-a-dehumidifier-cost-to-run/)

*"If the heating came on twice per day and needed to heat the home by just two degrees, then (35,000 cubic metres of air at a humidity of 75%) would equate to an extra usage of 9kWh per year, which depending on your electric company, could cost around £3-£5 pounds." - (https://getdehumidifiers.com/how-much-do-dehumidifiers-cost/)

*"EcoAir says, dehumidifiers can help cut energy costs: 'The higher the humidity levels the harder it is to heat a home, leading to higher gas bills.'" - (https://www.express.co.uk/life-style/property/928413/dehumidifiers-help-reduce-your-energy-bills)

Intuition
The central heating input counteracts the loss of heat through the exterior of the house. The humidity of the air does not change this rate, except for when condensation occurs (through latent heat of condensation).
It also counteracts outside air coming in, however given that that air will be colder, when heated the humidity will be reduced.
Calculation
The dehumidifier is bound by 1st law of thermodynamics, energy in = heat out. But it can move heat from the water into the air, as a heat pump.
Taking the 250W ElectricQ 10L dehumidifier, if it did produce 10 kg/L (of 10deg water) per day (at 100% dudy cycle) from 20degree air, it would remove energy from the water by the following calculation.
$\Delta H_{vap 20^\circ C} = 0.6816 kW~kg{-1}$ - (https://www.engineeringtoolbox.com/water-properties-d_1573.html)
$c_p = 0.00115 kWh~kg^{-1}K{-1}$
$$ \Delta E = 10*0.6816 +  0.00115*10*10 = 6.93kWh$$
However, it would require $0.25kWh \times 24 = 6kWh$, given gas central heating $2-3\times$ cheaper, this does not turn out cheaper. Also, it can only produce 10L @ 30degress 80% humidity, in reality it will produce much less.
Is my calculation correct? What other factors should be considered?
Other possible myths encountered
"Will it heat my home?" - "Yes, but ... the warmer the room, the easier and more efficiently you can remove moisture so the machine will have to work less. " - (https://getdehumidifiers.com/how-much-do-dehumidifiers-cost/)
Surely this is only if the humidity goes up, which it won't? The Enthalpy will remain the same. -
 A: The answer to this question approaches things from another direction, but it seems the most practically useful way to answer:
It's common for people to try and reduce their heating bills by cutting out any draughts, shutting all windows and vents etc. so that the warm air will stay inside the house.
This is a false economy however, reducing ventilation increases the humidity in the house and causes other problems such as damp, mould etc...Moisture is constantly being created in a house by cooking and showers and a damp house will never feel warm in winter, so it's vital to maintain good ventilation.
To reduce the humidity in the house, two things are required.  Heat and Ventilation.
The heat allows warm air to hold the moisture, evaporate moisture from furniture etc. and the ventilation then allows this moist air to be removed from the house and be replaced with air of lower humidity.
The effect on the heating bills of having good ventilation is negligible, but your house will feel warmer and less damp as a result.
So allow a route out for moisture by keeping slightly open a ground window, or vent and one at the top of the house such as a loft or upstairs window or vent.  Open windows often - especially in kitchens and bathrooms.  The dehumidifier is an unnecessary expense if you have adequate ventilation.
You may even save money on heating as it'll take less heat to make a dry house feel warm, as apposed to a damp house.  Hope it helps!
