Over the top: the external heat pump unit - up high and out of the way


Tuesday June 6; Tuesday June 13

The Best Laid Plans

The original idea for heating 60k House was to install a small wood heater. Actually, the initial plan was to see how effective the passive thermal design was before deciding if I even needed any additional heating. I wasn’t around for winter last year – the house wasn’t even finished yet. This year I had a small, portable, efficient convector heater that I could move around and plug in where required – either the living area or the bedroom. During the month of May I used the heater half a dozen times – not a bad effort. The passive design of the house was working – good orientation, double-glazing, exposed thermal mass (polished concrete slab and recycled brick wall). But on occasions the space just needed that extra boost. It was optimistic (naive) to think the house would be warm enough on the coldest nights and days in winter without additional heating.


What were my options? Early on during the concept stages of the design my colleague and I talked about using a reticulated water system, heated in pipes on the roof by the sun and circulated in pipes within or on the face of the dividing wall. Apparently water has four times more thermal mass than concrete – and you also have the ability to drain it away when you don’t want it. This would have been a simple and low-tech solution, but somewhat untested, at least in Tasmania or by myself. Having just spent a month in Europe where water radiators are commonplace I kind of regret not giving it a go at my own place, or at least investigating this option further. One of the ideas for 60k House was to experiment with previously unused materials and techniques – I have done this with some elements but maybe could have been even more adventurous. The type of experimentation where the results are going to be unknown until you build it, the type of experimentation you can only do on your own house and not on your clients’. The solar water heating idea will have to wait for now – until I design a house for my mum.


I don’t consider fixed panel heaters to be very efficient or cost-effective, even if they are wired in on the off-peak tariff, so I didn’t give them much thought at all. That left two options: the original plan of a wood heater or a heat pump. I should mention that in Tasmania (and possibly other parts of Australia and the world where the climate is cooler) reverse-cycle air conditioners are more commonly referred to as heat pumps – that’s what I’m talking about.


The location of the would-be wood heater was considered and prepared for: it would have sat just to the south of the ridge so the flue would not interrupt any future solar panels on the north. We also ran a section of brick wall up to the ceiling to back the flue against. Before I went away last winter I looked into the cost of buying and installing a wood heater then began to have second thoughts – the total cost would have exceeded $2,500. This would have included a decent small unit, flue kit and extension kit (because the height from the unit to the roof outside was longer than standard), and the installation.


Up-front cost wasn’t the only factor to consider: ongoing running costs, temperature control, ease of use, time to warm up, space it takes up, proximity you can store things, ability to stand close and warm up, ambience, noise, smoke, dust, etc. Heaps of things!


Being on a bush block I have an endless supply of firewood – but it takes time to cut, split, stack and wait months for it to dry. A heat pump is energy efficient – producing around 4 times more energy that it uses. It’s much easier to control the temperature coming out of a heat pump than a fire, and a fire takes a while to warm up.


The prospect of listing my house on Airbnb also became a big consideration – having people stay from warmer climes, possibly unfamiliar with lighting fires, favoured installing an easy-to-use heat pump.  Not taking the brick wall that divides the living area from the bedroom to the ceiling lent itself to a form of heating that could blow warm air up high through the large gap beneath the ceiling.  On the balance of all this I opted to install a heat pump. Sure a raging fire in a wood heater would look good in photographs and add a certain ambience, but the ease of the heat pump won out.


I contacted a heat pump installer through Sustainable Living Tasmania and arranged for someone to visit the house, size a unit and provide a quote for the unit and installation. He recommended a 5KW cooling / 6KW heating unit to heat the living area and bedroom, and gave two quotes for two different brands – both around $2700. I also asked Alan my electrician for a quote to install any unit I supplied. One of the large electrical retailers then had a sale so I went and bought a unit and arranged for Alan to install it.


There are currently two schemes operating in Tasmania to help people purchase energy efficient products: the TEELS scheme (for purchases up to $10,000, available to everyone) and the NILS scheme (a rebate available to concession card holders). I paid for my heat pump up front but have ordered some solar panels through the TEELS scheme – will explain more about that in a future blog post.


The store I bought the heat pump from didn’t tell me it had to be transported standing up – until I arrived to pick it up in my car. Wheel it back into the warehouse buddy – I’ll be back in a few days with my mate’s ute.


I hadn’t planned for a heat pump during construction and was keen to minimise the amount of conduit and pipes on display – this was one reason why I got Alan the electrician to install it so I could work with him. First we needed to get the power cable from the meter box up into the ceiling cavity and then out through the wall where the external unit would be. This involved removing some timber cover strips and a piece of cement sheet cladding – unavoidable but easily enough fixed or replaced. We also needed to locate the structure behind the cladding where the unit would sit – the cladding is packed out on timber battens but we wanted a good fix onto the studs and top plate behind.


Fiddly: Alan running the cable from the meter box through the top plate into the ceiling cavity


Not my best photo: crawling along the trusses in the ceiling cavity to locate the wall structure and feed the cable through


There is very limited crawl space in the ceiling cavity between the widely spaced trusses and the glass fibre insulation batts doesn’t make it a pleasant experience. This was my oversight, I wasn’t going to ask Alan to get up there. Alan was good enough to lend me a beanie with an LED light on it. I hoisted up a couple of planks to crawl along and worked my way along from the ceiling access hatch in the entry to the far end of the building. I retrieved the wire that Alan had fed through the top plate, poked it through the end wall, and measured the stud and plate location. About 45mins later I had my feet back on the ground and breathing the fresh Channel air. We bolted the bracket that would hold the external unit and added an extra bugle screw for good measure.


On the level: fixing the bracket for the external unit


Thinking: using Alan’s ute as a work platform – a damn sight easier and safer than balancing on a ladder


A week later Alan came back to fit both the external and the internal unit and commission the system. We used the back of Alan’s ute as a work platform as we lifted the heavy external unit into place. The internal unit is much lighter and easier to use, with a metal plate/bracket screw fixed direct into the plywood lining (we made sure to hit a few studs too). Bewilderingly the cable from the internal unit comes out on the opposite side as it needs to be connected to the external unit. Alan did a good job minimising the conduit and exposed pipes so it doesn’t look too unsightly or an afterthought (even though it is ugly and was extra).


Easy does it: Alan installing the much lighter internal unit


Nip and tuck: trying to minimise the conduit and exposed cable


Since I’ve been back home winter has been harsh – some days not even making it into double figures. But the passive solar design still works during the day and the heat pump gives a much appreciated boost, making 60k House toasty and warm.


Minimal: the internal unit installed


Spot the difference: the external unit hidden up high and out of the way


Costs: heat pump – $1318; installation – $770


Disclaimer: Any advice contained within this blog is of a general nature only and cannot be relied upon. Details provided are in good faith and relate specifically to this project. Any author will not be held responsible for advice or information presented.



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