Why old homes can be easier to make energy efficient than new builds

The first thing energy efficiency assessor Lucinda Flynn does when she visits a house to conduct an energy assessment is sit down for a chat.

A key feature of home energy efficiency assessments is they are individualised, based on tailored conversations that focus on the specific needs of a household, rather than generalised information about electrification or energy efficiency.

“The first thing we do is sit down at the kitchen table and just talk about the house and the people that live there, how it works for them,” Lucinda Flynn told the SwitchedOn podcast.

“And then I look at the house in its construction and the main fixed appliances, and then work out the things that are going to have the best effect for them.”

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Flynn has conducted hundreds of home energy efficiency assessments and in the process saved households thousands of dollars.

On average, many of the houses Flynn visits in Melbourne only have a 3-star energy rating. They’re likely to have been built in the 70s or 80s and are poorly constructed. They’re draughty, have ducted gas heating and gas hot water supply, little or no insulation in the ceiling, and no insulation in the walls.

“My goal is to identify a whole lot of upgrade opportunities, and then demonstrate using the [Residential Efficiency Scorecard] modelling how people can get to a 10-star home, which means that they are generating more dollar value of energy than they use in the year.”

Despite the challenges involved in taking existing houses to a 10-star rating on the Residential Efficiency Scorecard, Flynn says she would “take an old build over a new build any day if it was about efficiency.”

“Older houses are often easier to improve than newer houses because they're smaller. They are already built in a way that includes zoning of different areas, which means you can reduce your heating and cooling to the zones that you're actually using.”

This is because heating costs are directly related to how much space needs to be heated.

“If you're heating an entire house, it's always going to be a lot more expensive than if you're able to heat and cool smaller areas.”

The problem with newer builds is that they’re much bigger, they usually have ducted heating, and they're often two storey.

“That in itself is such a massive amount of air to be conditioning,” says Flynn. “It's hard to work out how to reduce energy costs in a house like that because it's just not designed to make that easy.”

Depending on householders needs and budgets, Flynn may simply help with basic, and cheap, solutions like draught proofing, curtains, and zoning. When it comes to appliances, heating is high on most people’s agendas.

“I pretty much always suggest swapping over that heating first because it's such a high use of our annual energy,” says Flynn.

“At least half of the energy we use is usually on heating, and it can be up to 80%. So if you can change from using gas for that to electricity, you've reduced your gas use then say by 80%.”

The most efficient heating system is a reverse cycle air conditioner, and in particular a multi-split reverse cycle air conditioner with multiple indoor units connected to a single outdoor unit.

But multi-split air conditioners don’t suit everyone’s needs, and a common response from many of the people Flynn sees is that they don’t like the blowy feeling of household air conditioners.

Flynn says this is because many people’s views are based on their experience with older style air conditioners which don’t have inverters: “It's just on, bam, and it's off, and there's nothing in between.”

Modern air conditioners aren’t blowy because they generally have inverters which regulate the speed of the compressed motor. This enables them to “cycle slowly on and slowly off so that you barely know they're doing anything.”

Flynn also says your building shell has a really big impact on how appliances like air conditioners work.

“If your building shell is leaking heat out of it, either through drafts or very inefficient thermal windows or lack of insulation, whatever your heating is it's going to be working flat out to try and keep enough heat in that room to stay at temperature.”

“The moment you start improving your building shell you will notice that your heating will just slow down, because you'll get to temperature in a shorter time.”

Whilst the ultimate goal is electric reverse cycle heating and cooling, an induction cooktop, and a heat pump hot water system, Flynn concedes that if you've just installed a bran- new gas appliance, there may be other things that can be done first to reduce energy use.

“I saw a house that had an evacuated tube solar hot water system with a gas booster that wasn't that old,” says Flynn. “That's a really efficient system still, and if they just want to turn off gas, then yes, they can replace it. But if their budget is limited, then there are other things.”

Whilst many energy experts regard the decision to get rid of a gas stove and replace it with an induction option is a ‘gateway’ decision, one that pre-empts getting rid of gas entirely, Flynn says the stove is often the last thing people change.

“I generally say, once you get to the point where your heating and your hot water is electric, then that's the time to change over your hot plate, because that will save you the dollar a day service charge [for being connected to the gas network.]”

Just as people need tailored individualised advice, Flynn says they also need first-hand experience of electrical appliances like the new air conditioners, induction stoves, and electric vehicles work.

“We need to feel it and experience it to really know that it might be an option,” says Flynn, who recommends people talk to other people who use these appliances, or, attend a clean energy expo which offers induction cooking demonstrations, or EV driving experiences.

You can hear the full interview with Lucinda Flynn on the SwitchedOn podcast here.

And you can find more information about Lucinda Flynn and home energy efficiency assessments here.