I have been saying for years that when our fridge/freezer gives up the ghost I will replace it with a chest freezer converted to run as a fridge. From an energy perspective, it's a no brainer. A chest design is superior for keeping the cooled air in when you open the door, rather than letting it all rush out as an upright model does. You could DIY the conversion if you were that way inclined, but you can also purchase a kit that simply piggybacks on the power point, puts a temperature probe in the freezer and controls the motor to run the 'freezer' at fridge temperatures (see details here). An advantage of this set up is it's removable, which won’t be the case if you've replaced or modified the thermostat instead. The kit sells for $150 (or a DIY one for $30) and Tom's conversion uses just 100 watt hours a day (that's about a tenth to one-twentieth of the average energy use of your typical upright fridge/freezer).

Enter our existing 385L fridge/freezer. Firstly, it had a quite good energy rating when purchased about 10 years ago, with 5 stars for its use of 530 kilowatt hours (kWh) per year (yes, it still has the sticker on it!). However, monitoring with a powermate over the years has shown it rarely performs at that rated amount, nor even close for much of the year. Even in recent mild weather it's averaging 1.8kWh per day - which is more than half our (admittedly very low) total electricity use. It has been internally icing up (between the fridge and freezer), it's been visited by the fridge doctor and pulled apart, fixed, adjusted and reset by Build-it Bloke more times that he cares to remember. The last couple of times it has happened we've had food perish so it was time to think about replacing it.

Despite my long-held desire for the chest freezer conversion, I wouldn't be an energy nerd if I didn't consider ALL the options. So, with the help of Choice, energyrating.gov.au, various other internet resources and eventually some visits to whitegoods retailers, we set about weighing up the options.

Some factors that came into the mix:

• I discovered our existing fridge's energy rating was amended (sometime after Build-it Bloke bought it) to 611kWh (no wonder it has trouble hitting 530kWh!).
• The energy rating for fridges has recently been upgraded. This is a good thing - we're moving to greater efficiency. Yet as it's a transition period many manufacturers are still using the old system - and who wouldn't when 5 stars becomes 3, but you can continue to promote '5' until the transition is over? Problem is, a consumer just looking at stars is easily misled with this inconsistency. So it's really important to look at that 'use in a year' kWh figure instead.
• The most efficient brands (Vestfrost, Elcold, Gram) are difficult to get hold of in Australia and are comparatively expensive to purchase relative to the more 'mainstream' models (although they have traditionally far outperformed the latter in terms of energy efficiency, due to superior insulation and function).
• Smaller is not always more efficient. Some smaller fridges actually use the same amount of energy as their larger counterparts. Certainly you want to match the size of the fridge to how much space you're likely to need, however, if your requirements are on the low side (and with just two of us, ours are), sometimes you find that the model a size up actually uses the same (or less!) electricity.
• For fridge/freezers, models with bottom-mounted freezers use more energy than top-mounted models.
• Energy ratings are based on testing where the doors are not opened and closed. So, as we all know, the impact of your household's habits can be significant on the appliance's performance.
• We have a small house and the current fridge is located in the back room because there’s not an appropriate space for it in the kitchen (!).

So what have we bought?

Well, we didn't go for the chest freezer conversion! It turns out that even Energy Nerds can realise there's more to it that just getting the lowest electricity consumption possible.

While I think we would have coped with the inconvenience of trying to arrange a chest freezer (converted) to allow frequent access to fridge items (and our backs are in fair shape, where others may find it challenging), the issue is space. Although we don't require an enormous amount of freezer space (no whole beasts to slaughter and freeze from our little block) we aren't ready to go without one altogether. So that would mean running two chest freezers - one as a fridge, one as a freezer. But would struggle to find space for them in the house (and the inefficiencies of running them in a shed or outside aren’t for me). We decided that a combined fridge/freezer was a better option for us space-wise.

I must admit we were a little surprised when I did a comparison of the various options, that this apparent 'compromise' wasn't nearly as big a deal from an energy perspective as I expected it to be. Below is a summary table, but I'll try to give you an overview in words, which might make more sense.

Ok, so scenario one is to buy two chest freezers and convert one to a fridge. We could go for the cheapest we can find (in this case 150L each) at $750 to buy and convert, or the top of the range Vestfrost ones (239L) at about $4,150 to buy and convert. Both these options would attract very modest running costs per year at current prices - $65 for the 'cheapies'; $52 for the Vestfrosts. If you consider the purchase price plus the running costs for 10 years, the 'cheapies' come out about $3,000 ahead. Vestfrosts would total $4,700; 'cheapies' $1,400.

But I've already identified some issues with that scenario for us, so what about the other options? Well, one that jumped out was a Fisher & Paykel upright fridge/freezer (283L/97L for those compartments respectively), with an annual energy rating of 417 kWh and purchase price of $899 - making it's total costs over 10 years $1,733. Economically, that's better than the Vestfost and not that far off the 'cheapy chests'. Also in the ballpark was an Electrolux upright fridge/freezer (313l/103L), with a rating of 349kWh and ten year total of $2,198. Hmm, so this second model is more efficient than the first but the purchase price is higher.

And of course in that higher purchase price, you're not just paying for efficiency. There are a whole swag of other features (which may or may not be important to us!) and indeed, in this case, both the fridge and the freezer have larger capacity, too.

In an attempt to better compare "apples with apples", I also did some calculations to give a 'factor' that accounted for volume as well as price and/or efficiency. At this point the fridge/freezers started to look even more attractive. What's more, as energy prices rise (and there's no doubt about that happening), they pull further ahead.

So, on a per litre of volume basis, in both energy consumption and costs (purchase price plus running costs) there are models of upright fridge/freezers out there that can compete in performance against a chest freezer and chest 'fridge'-conversion.

As if that wasn't a surprise enough to me, we went a step further and ended up buying a bottom-mounted freezer model. Part of the appeal here was that places the fridge at body height. We think we'll be able to better use the fridge space and reduce the amount of time we need to have the door open looking for what's usually at about knee-level. Also, the bottom-mount in the brand we were considering actually had a larger freezer than their top-mount counter-parts. While this also adds to the electricity consumption, we think a bit larger freezer matches our storage needs most closely (our current one struggles when there’s a glut from the garden or friends), without need for an additional appliance (ie fridge/freezer plus chest freezer). In the longer term, we’re interested in expanding our abilities to store and preserve food without ongoing refrigeration (or could perhaps rely on a single chest freezer converted to a fridge with no freezer?) ... but we’re still a way off that.

I couldn’t find any information about relative embodied energy of the specific models, but as a large appliance, we certainly want a long-lasting quality purchase (with replacement part availability) rather than having to go through this whole process (and rack up the associated manufacturing, transport, etc. energy costs) again anytime soon. And yes, we’re working on what we’ll do with the old one to reuse it, rather than scrap it.

The bottom line is that we didn’t buy the most energy efficient option in absolute terms (the conversion) and we did pay more than the cheapest purchase price option in the class we ended up considering. However, we will save on the running costs and we still expect to the new fridge to use at least a third less electricity than the previous one even though it’s larger. Convenience, space availability, refrigeration/freezer space requirements as well as energy consumption and purchase/running costs were all considered. In the end paying more upfront for a ‘best in its class energy performer’ but widely available model, which happens to be Australian made, was our preference. Of course everyone's situation and priorities are different - and therefore others would make other choices.

Our final decision was much along the lines of most Aussies (ie it's an upright fridge/freezer) but we’re happy to have gone through the process to understand how much we’re paying for the convenience and space advantages, compared to the cheapest to purchase and run options.

We feel we’ve made an informed decision, rather than just a decision.