I bought a patio heater to enjoy evenings in the garden, but now I'm worried I'll get a massive energy bill - how bad are they?

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I recently bought a plug-in free standing infrared patio heater that comes with three power settings – 650w, 1350w and 2000w.

The top level setting has been wonderful while reading in the conservatory and we plan to use it frequently on those summer evenings when the temperature drops, but we want to stay outside.

However, I am worried about the running costs and how much it could add onto our bills. Are they energy guzzlers?

We will typically use it for around 12 hours a week, all-year around, mainly to use in the garden for summer and conservatory the rest of the time, I imagine on the top setting. 

Switch on summer: Eating outside in the summer can be one of life's great pleasures

Lee Boyce, consumer affairs editor at This is Money, replies: As we have written before, a conservatory can become redundant in the winter thanks to it being too cold.

Meanwhile, there is only a small time frame in Britain in which we can realistically sit out in an evening without shivering and calling it a night.

A good patio heater is not a bad bet for prolonging conservatory use throughout the year and to keep you out in the garden long after the sun has set.

But you are right to be concerned about what this could do to your energy usage. 

Anything that produces that kind of concentrated heat is bound to be expensive.

Let's take the 2000w - or 2kW - top level setting. 

This will cost roughly 31p an hour to run, based on the average UK tariff.

If you have this on in an evening for three hours, this would mean nearly £1 of usage. 

Using your example of 12 hours a week, it would cost £3.72.

Over the course of the year, this would equate to just shy of £200.

If you turn it down the middle setting of 1350w, this would cost more like 20p an hour. 

This would mean a slimmer £125 a year to run the heater - but might not be enough to keep you toasty.

This may not sound like an awful lot of money to some – but compared to a big appliance such as a fridge freezer, the amount of energy this will guzzle is huge.

Feeling hot, hot, hot: The price of running your infrared heater is high when you compare it to a fridge freezer

For example, a typical A-rated 180-litre fridge freezer costs roughly £40 a year to run while a bigger 500-litre fridge freezer with a higher A+ rating costs around £50 - and this is switched on 24 hours a day, 365 days a year. 

Furthermore, you might end up using the patio heater for longer than you expect and this could add a surprising amount onto your energy usage. 

Then again, if it helps prolong those summer evenings, perhaps it is a price worth paying.

As Cat Stevens sings, you really can: 'switch on summer from a slot machine'.