Saturday, April 11, 2015

Winter approaching, roof work, more solar

I have been busy preparing my house for winter. Last winter (the first in this house) we did little apart from install curtains, and the interior of the house regularly dropped to 13 C on cold winter mornings. To be honest, this is quite bearable, especially with the electric blanket we use on the couch when reading or using the computer. But, it would be nice if the house was a bit warmer in winter.

Heat retention

Before working on heating, it is vital to minimise heat loss, otherwise any heat just rushes out of the house again. This has two main parts:
  • drafts -- do this first. Drafts are a killer
  • insulation -- stop heat conducting out
Our house is very drafty. Here's what I'm doing (work in progress):
  • go around the entire house with a caulking gun and seal up all the skirting-board to floorboard interface with gap filler
  • go around the ceilings, and fill all the gaps where the light supply cable penetrates the ceiling
  • put door skirts on all external doors
  • put rubber seats around all external doors so that they seal
  • Install a DraftStoppa on the bathroom exhaust fan
  • replace the kitchen exhaust fan with a proper (closing) duct that goes outside the roof
If I get time, I will also
  • remove all light switches and power points in cavity walls and seal the cable penetration
  • work on the windows to improve their seal
though, I suspect this might take until next year.

In parallel to this, I have also put a heap of insulation (rockwool) in the ceiling. There was insulation already, but it is old, dirty, compressed and thin and I just laid the new on top of the old, hoping that was adequate. I really didn't want to disturb 40 years of rat urine in the existing insulation! This job is only 1/2 done -- it's very easy to procrastinate going into the roof...
I have also started planning to retrofit double-glazing to some of the windows. For some windows, this will be easy. For some, hard. I'll leave the details of this to another article in the future.


Once the house is better at retaining heat, it will benefit from having more heat injected into it. To do this, I have started building a solar space heater from some salvaged material I had. Here's what I've used:
  • some corrogated iron, from the carport I pulled down
  • some light meranti timber from the pergola I repaired
  • Some other salvaged timber of unknown heritage
I snapped a few photos as things progressed:
Materials I am using, mostly reused except for the roll of plastic sheeting top-left

Beginning of the framing. I decided to make the frame to fit the plastic sheeting rather than the iron. This means that the frame is wider than the iron, which was a bit awkward to fill without cutting a long thin bit of iron (which I didn't want to do for waste). I had a couple of pieces of flashing lying around, which I was able to rivit to the iron and seal.

The unit on the roof. I decided to use an existing TV antenna to support it. As we don't have a TV, it's good to see the antenna is finally good for something!

Another shot of it installed on the roof. A rear brace is visible. It's important that it is anchored well, as it's a bit like a giant sail on the roof. Note the aluminium rails on the roof. I used some solar PV brackets that slide under the tiles and anchor to the roof purlens. I hope it's strong enough!

A closer shot of the side. I also used tin to help anchor the struts to the frame (stop the nails pulling out). I've angled it quite steeply (over 70 degrees), so that summer sun won't make it too hot (this is because the sun is higher in the sky in summer)

A view behind. Here you can clearly see the flashing, as well as the two struts and the anchoring to the TV antenna. I plan to put in a third strut. Behind it, you can see a 30 L solar hot water system that will supply only the kitchen. More about this in a future post.

 Next step

I will buy some ducting, and a through-tile to let me get the ducting into the roof. I'll need to work out an air blower and switching. I need to insulate the back of the collector (to reduce heat loss). Note too that the unit needs to be quite well sealed, otherwise cold air will reduce its efficacy.
EDIT: I forgot to mention that I also need to paint the inside of the box matt black, and cover the front with the roll of plastic shown in the photo. I'll also put some small vents along the bottom of the box for fresh air to enter (although another option is for the box to accept air from the house, heat it and return it through a second duct -- I'd rather have fresh air I think).


The collecting area is 3.1 m by 1 m. Assuming I can get it working fairly efficiently, I think it should be equivalent to at least a 1 kW bar heater in the lounge room when it's sunny. It might even be as good as a 2 kW heater. Time will tell...

This post was written by Angus Wallace and first appeared at


  1. Wow, Angus, if that heater is effective as it is simple, it will be amazing! I am interested to see how it goes..

    Our post-renovation/double glazing (but not all windows) /curtains/blinds/insulation/mostly draught-proofed house gives us 13C winter mornings! Clearly it isn't retaining heat as well as it might - but also our nights are much colder than yours I guess.

    Do you think insulating behind light switches and power points makes a big difference? If so, I will get onto that. Also, we have a back door with a glass window in it. That is on my list of things to tackle to reduce heat loss.

    Other than that, for windows I have found close fitting blinds with lined curtains in front of them are very effective, even more so with a pelmet fitted above the floor length curtains to stop air-flow past the cold window. The old draughty windows in our living room responded well to this treatment - no draughts detectable from them any more:)

    When we renovated we went to a more open plan style. Which is nice - except for keeping warmth in one place. It is possible that the folks who built this house in 1930 really had the right idea with the small rooms with solid doors..

    One very effective, simple change we made was installing a draught stopper in the chimney for our open fire place (yes, I know this is not very efficient..). It is a metal plate installed in the top of the chimney, opened and closed via a little chain in the fireplace. Keeps draughts and rain out, just need to remember to open it when we light the fire...

  2. Hi Jo,

    I'm not sure if it's clear from the post, but I also need to paint the inside of the box matt black, put the plastic over the front of the box and seal it (I've added a bit to the post to clarify that), but yeah, it's pretty simple! There are a few docs around the net about this kind of thing.

    Regarding stopping drafts coming through light switches, it probably depends a lot on your house. For example, for an internal (single) brick wall, it probably won't let a draft through because the hole doesn't go anywhere. On the other hand, if it's a cavity or stud wall, then there's a path to outside and a draft can get through. Hope that makes sense.

    Thanks for the reminder about the chimney -- another thing for my to do! ;-)

    Regarding your thoughts about winter warmth in your reno, its performance will be largely affected by the unimproved windows. For example, if you have two single glazed windows and double glaze only one of them, you might expect performance 1/2 way between single and double glazing both windows, but the performance is generally quite a bit closer to two single glazed windows than you might expect (think of the phrase "the weak link in the chain")

    Cheers, Angus

  3. Hi Jo,

    I realised I never replied to your comment about ethics...

    I think there's a fine line that needs to be trod. We need to make people aware that there are pressing problems, but we need to articulate a positive vision of how things can be different and encourage action (rather than being critical of the present state of affairs).

    If we are too negative, we risk the "oh well, we're screwed and there's nothing to be done" reaction. This is why I think the transition town movement and (eg) Costa Georgiadis on Gardening Australia are so good -- their enthusiasm and verve are inspiring to all.

    Cheers, Angus

  4. Angus, thanks for your great replies! It is so good to talk to someone knowlegeable about this stuff!

    When we renovated we put a big bank of windows on the north side of the house - they let in huge amounts of winter sunshine which means sunny winter days we don't need to use heating, which is brilliant BUT of course they let winter night cold in as well, hence the choice to go double glazed with them. But yes, we also have unimproved windows as well.

    Our house is 1930s weatherboard, as are most places in Launceston, and until we started renovating, completely uninsulated. Folks here must have frozen all winter in the 'good old days'. Whenever we removed part of a wall we insulated in the cavities, and the ceiling of course, but it is nothing like as snug as new builds can be nowadays.

    However it is way better than it used to be! So, in answer to your question, yes, all our light switches and power points would be in cavity walls. What sort of insulation do you put behind them?

    And yes, totally agree with you on the ethics front. I like JMG's 'Butlerian Carnival' concept, and yes, that Costa is insanely enthusiastic. My efforts on that front are directed to finding ways to make my three teenage daughters want to come with me on the 'crazy-eco-lady' journey. And like you say, it is finding the balance between showing them how dire things really are for their futures, and then immediately introducing them to interesting and attractive ideas for change.

  5. Hi Jo,

    Glad I can help. Behind the switches is a hole into the wall where the cable goes. If that hole leads to the outside in any way (eg, down the wall, under the floor, out the under floor vents) then it will let drafts into your house. It's not so much insulate it as bog it up, so any gap filler will work fine.

    We had a weatherboard house when we lived in Brisbane. No insulation and no thermal mass. It got down to 7 or 8 overnight in winter. In the good old days, people probably had the range burning all winter...

    Cheers, Angus

  6. Hi Jo,

    It's important to remember that behind the switches are live wires (even when the switches are off). You should exercise appropriate caution or speak to an electrician if thinking of doing this.

    My place was built in the 1950s and has much of the original wiring. Its insulation is now quite perished -- handling the wire tends to cause the insulation to disintegrate, which is a big hassle and dangerous.

    Cheers, Angus

  7. Hi Angus, thanks for that info and will of course be careful! My ex-hub is an electronics engineer so will probably ask for advice next time he visits.

    He rewired our whole house during renovations - then had it signed off by a licensed electrician of course. We had original rubber coated wiring running in wooden channels, much of which was missing some of its rubber coating. We are lucky the house didn't burn down!

    Anyway, all wiring now safe, which is excellent!

  8. Hi Angus,

    If you get a chance, a couple of RCD (return current devices) units in the fuse box wouldn't go astray as they'll give a bit of protection from short circuits. Top work with the heater box. As a suggestion have you considered using a extra low voltage fan to save the hassle of having to explain your heating unit to an electrician? 12V or 24V DC is all quite legal. You'd have to run a transformer from the 240V though. The brand "Meanwell" make some outstanding transformers - I use a 24V DC to 12V DC transformer for garden lights here and the unit is very good and very well built. I picked it up from:

    The DC fans are usually sourced from car or truck thermo fans and ebay is full of them. Do a search on say 12V fan and you'll get lots of hits. You probably want a high volume fan.

    A really clever design would incorporate a solar panel which only switched the unit on when the sun was shining, but personally, I'd opt for the simpler switchable fan as you may not want the unit operating over summer. DC Fans can also operate in reverse by switching the positive and negative wires so you could suck warm air out of your roof space on a hot day too. Just thinking out aloud really.

    Top work! Chris

  9. Thanks Chris,

    Those are all good thoughts, and I haven't completely worked out how I'm going to wire up the blower. I got an electrician to put a power point in the roof a while back, so that helps. What I was thinking was wiring up something like this
    in series with the motor. Put the sensor in the box. that way the motor only pumps when the temperature in the box is above 40 degrees...
    Yes I have an RCD already -- but I still won't be cavalier about the power! ;-)

    Hmm. Might think about getting a 24 V blower though -- a bit safer to mess around with those kind of voltages...

    Great idea about sucking out the hot air too. I'd thought about that myself and was trying to think of how to integrate it :-)

    Is your whole house running on 24V?

    I saw your comment on ADR about older style regulators/inverters with PWM instead of MPPT. That's interesting. Could I pick up one of those older (cheaper!) ones and use it as a hybrid inverter? I'm not ready to take my house off grid, but would love to experiment with load shifting... Not sure how I'd integrate something like that with my grid tied solar PV though...

    Thanks for you ideas :-)
    Cheers, Angus

  10. Interesting. I hadn't heard about one of those thermostats. So the circuit closes when the temperature hits 40'C and then re-opens at 25'C. Not a bad idea. I reckon that switch would work with DC as well - as long as you didn't exceed 10A current which is a pretty meaty fan. It looks as though it works by only switching the Active or Neutral in an AC circuit, so you could simply try it on the positive wire in a DC application. Just remember to put fuses on everything (super cheap auto will have fuses and fuse holders for low current DC applications eg. vehicles 12V and trucks 24V). ;-)

    Well, in Victoria you can wire up to 120V DC (50V AC) no problem, so I don't see why SA would be any different.

    Yeah, the good thing about a lot of DC fans is that the wires go one way it blows and the other way it sucks. You can easily test that too - just watch out for your fingers and the blades of the fan... Ouch. I use a truck thermo fan to blow cool air into the battery room from under the house during prologned heat waves. I haven't used it much, but it does make a difference.

    12V DC, 24V DC and 240V AC. Visitors can't tell that there is anything unusual about the power supply as the inside of the house works exactly as per a normal house - It just has a maximum upper limit of 9,000W supply for the 240V. Most grid connected houses have an upper limit of 13,980W. They're both huge amounts of supply.

    You could easily do a 24V DC house, it is just expensive as the copper cables would cost a small fortune (the amps required to supply appliances would be huge). Basically an appliance that uses 1A at 240V = 240W would require 10A at 24V = 240W. Hope that makes sense. A x V = W

    Well, there are two parts to an off grid solar power system. The regulator which is the brains that controls the battery charging process (thus the PWM vs. MPPT business) and the inverter. Your grid tied inverter is unable to be used in an offgrid application. The difference is this:

    -Grid tied inverters are like a constant pressure pump in that they supply electricity (or water if you are thinking about the constant pressure pump) at full speed with no ability to slow the flow.

    -Off grid inverters are like a pressure sensitive pump in that they supply electricity only when required and only in the amounts that are required. They are a much more complex and thus more expensive inverter than the grid tied unit.

    But yeah, you could easily have a second stand alone off grid power supply for your house. A very small one would be 12V, 24V is more useful (pumps, lights, fans, all sorts of other appliances are still availble), whilst 48V is often seen too (petrol generators are hard to find for 48V systems though). I run 12V on the shed and 24V for the main house solar.

    A lot of the parts can be scrounged, but it will still cost more than a few hundred dollars, but once it is there, you've got a second power supply that makes no noise and just does its own thing.




Creative Commons License
This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.