[nudephil (OP)]

Here's a message sent in by listener Steve:

Heat pumps are one option to reduce the demand for gas or oil to heat our homes. If all gas or oil boilers in the UK were swapped for air source heat pumps we would change from hot emissions to cold emissions. Would this have a measurable impact on winter temperatures?

[Petrochemicals]

In the obvious answer, yes, less energy would be consumed via fossil fuels so there would be less energy, but overly the difference in temperature would be neglegable.

This small difference in energy however would lead to less evaporation and cooler air meaning that the atmosphere as we know it would contract leading to a cooling cycle, meaning that the ground level temperatures would drop .

[MarkPawelek]

I suppose it may reduce the urban heat effect marginally, but that's not really a climate effect it's an effect on thermometers. 95% of people live in 5% of the land mass. So 95% of land has only 5% of the world's population. Heat pumps will only be installed in the Northern Hemisphere. So the answer is not that anyone will notice.

A more sensible question is how much will they cost?, and how well will they work in coldest winter and what will happen if we have another (cold) winter like early 1963?

[evan_au]

Another name for "air source heat pump" is "air conditioner".
- An alternative is "ground source heat pump", which doesn't affect air temperatures so much (I think alan has one?)

We also need to specify which temperatures:
- Inside temperatures: Unaffected. You leave it on at the level you feel comfortable (or that you can afford), for as long as you like
- Outside temperatures: In winter, moving heat from outside to inside will make it a bit chillier outside in the street.
        - In summer, moving heat from inside to outside will make it hotter and more humid outside in the street.
        - In New York, airconditioning is used in both summer and winter, making street temperatures more extreme
        - Summer cooling may be less of a concern in the UK, but with our trajectory global warming (due to burning carbon in the home, power stations and cars), it will become more of an issue in future decades

Heat pumps are one option to reduce the demand for gas or oil to heat our homes.

It is true that an airconditioner can move more heat than it consumes in electricity to turn the motor.
- But the savings in fossil fuels are not so great if the oil & gas is burned to produce electricity (the waste heat is thrown away), compared to burning it in your home (where the waste heat is the desired product).
- So it works best if the electricity comes from renewable sources (solar, wind, tide, etc)
- And it also works quite well if the heat from fossil power stations is harnessed for industrial or community heating.

It is also important that the heating/cooling is not wasted.
- In Singapore, airconditioners are continually struggling to suck heat from inside shops and dump it into the street.
- But the shops leave their doors wide open, so the cooled air flows out into the street, effectively "short-circuiting" the air conditioner!
- So air conditioners need to be installed sensibly and used sensibly