said by Kringle :

We have systems up here that only switch to oil at 5°F. I guess it all depends on what you figure is "very cold". I'm sure that you would still come out much further ahead if you only switched over at, say, 15°. You can use your calculations based on the efficiency curve of the heat pump and figure out a good switch-over temperature for your situation.

said by robbin :

That is only partially true. The part of the equation which is missing is the fuel source used to make the electricity. For instance around here in the winter time the main sources of fuel are natural gas and coal. Neither are particuarily efficient to convert to electricity (figure less than 50% with many plants operating at less than 40%). On the other hand, my natural gas furnace is over 90% efficient.

said by nonameyet :

No Natural gas in area, I could switch to propane?

said by CatSnak :

One thing many people forget is that the only true 100% effecient way to heat is with an electric furnace. It is the only heating device where you get a 1:1 ratio of BTU energy out for energy in.

said by CatSnak :

One thing many people forget is that the only true 100% effecient way to heat is with an electric furnace. It is the only heating device where you get a 1:1 ratio of BTU energy out for energy in.

said by hjghghkgk :

Sorry Kringle I missed some of the train of thought, but in the Lower 48 we are told that below 40 degree F we should switch over to fossil fuel or electric to due to heat pump efficiency.

said by cowboyro :

I will have to get the docs and based on that calculate what the "break-even" point is...

said by iu97987907907 :

Kringle look at your temps are they Fahrenheit or Celsius?

said by Kringle :

That seems like a pretty high switch-over temperature to me (mine's at 10.4°F). Do you have any control over that?

said by »www.hydroquebec.com/residential/···_dt.html :

Hydro-Québec’s dual-energy concept involves using electricity as the principal energy source and a fossil fuel (oil, natural gas) as an auxiliary source. Hydro-Québec’s dual-energy concept is particularly suited to the conditions described below.

Electricity is used for most of the heating season (i.e. outside temperatures above or equal to -12°C or -15°C, depending on the region) and the auxiliary source takes over when temperatures are very cold (below-12°C, 10.4°F or -15°C, 5°F). The switch from electricity to the auxiliary source is done automatically by an automatic switching device within the heating system that obeys signals received from a temperature sensor placed outside the home. (Note that the switch-over temperature is generally higher when the electrical component of the system consists of a heat pump).
The main dual-energy combinations are:
* a heat pump with a fuel furnace,
* an integrated dual-energy furnace (an electrical and a fuel component);

Dual-energy offers a more advantageous differential rate
With dual-energy, customers can better control their energy consumption because:
* Fuel is used at temperatures when it is most effective;
* customers who choose a dual-energy system conforming to Hydro-Québec standards can take advantage of the DT rate, which enables appreciable savings on their overall energy bill. (This rate is based on a differentiated temperature-based structure.)

Little electricity is used during the few weeks of intense cold each year, when the home is heated by fossil fuel. A signal light indicates high-rate periods, so customers can choose to delay using certain electrical appliances and thereby achieve additional savings.