23 Jul 2018

Beerhorses: the can-do DIY solar heating solution

From Afternoons, 1:31 pm on 23 July 2018

With a bit of Kiwi ingenuity, two Northlanders with a cold, drafty home turned some old cans into a nearly free-of-charge heating solution.

Terry Johnson and Mel McMinn's DIY solar-heater

Terry Johnson and Mel McMinn's DIY solar-heater Photo: Melanie McMinn

Terry Johnson and his wife Mel McMinn inherited the house Terry’s grandfather built in 1932, but after moving in they noticed the chill

“It’s a house that has always been quite pleasantly cool in summer and absolutely frigidly cold in winter,” Terry says.

“It had awnings over the windows so you didn’t get a lot of heat during the day, it didn’t have a lot of glass. It was a house that was built on a real budget back in the 30s.” 

“Originally it had no insulation whatsoever, then it had some … Batts insulation in the ceiling and extension work had some insulation in the walls. 

“The coldest times in that house would be on a frosty morning in winter, where it would be a sunny day but preceded by ice on the ground … inside the house we were seeing temperatures down to about seven or eight degrees.” 

Terry and Mel decided to improve things. 

“I demolished the awnings so that it opened up more light from the north and I stuck in some insulation under the floor,” he says. 

“I also bought a thermal camera so that I could walk around and see where the worst heat loss was occurring …  getting into walls in an old house is an expensive process if you just rip off all the cladding and so on, so I could go in and be more a surgical strike on the heat vampires.”

'Beerhorse' heater

After looking online at some cheap heating solutions they settled on the idea of a beerhorse, “because of people using beer cans to build them and the power that you get out is about 750 watts which is about one horsepower”.

“It’s sort of like having a one-bar heater running in the house for a few hours for nothing each day.” 

They collected about 300 cans from the local tip, painted them matte black and mounted them - stacked vertically - on a plywood board. 

Terry Johnson's solar-powered can heater

Terry and Mel collected fizzy drink and beer cans to make the heater.  Photo: Melanie McMinn 2018

“You had a opening at the bottom that would take air from the house at roughly floor level, then the air would enter into these columns of cans, rising up as it warmed up, and then exiting through a vent into the house near the top of the room. 

“What we did was just add a couple of low-power fans - like, computer fans - to just nudge the air through a little bit quicker and then it was coming out of the top vent at about 50 degrees celsius at about one cubic metre per minute, so it was a useful amount of warmth.” 

“I stuck it on the eastern side wall of the house so that it would catch the morning sun and it would just be over the period to just about 11 o’clock in the morning that it was producing useful heat, but that would raise the base [temperature] level of the house during the day. 

The heat pumps in thanks largely to the sun, and if it’s getting too hot in summer the top of the structure can be blocked off

Terry says it costs about $1.50 a year to run the panel, so is a really power-efficient way of heating a space, particularly for large open spaces that don’t get a lot of sun on the inside.*

“You get those kind of buildings and they would be impossibly expensive to heat if you were using electricity or gas, but if you painted one wall black, you put a membrane over it so that you can trap the heat and just have natural convection, there are a lot of people who have heated up that kind of space very effectively for essentially no cost.”

The pair sold the house four years ago and moved to a more modern place when Mel’s health deteriorated, but said the new owner insisted the beerhorse be included in the sale. 

Terry isn’t interested in making a career out of it, but says some companies in Canada are doing it at a commercial scale. 

* This has been corrected from the original which said the panel cost about $1.50 a day to run.

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