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Heat transfer fans with a heat pump and HRV style ventilation systems

Heat transfer fans and a heat pump. This combination is not recommended by heat pump manufacturers and suppliers, firstly they are concerned that you may bugger the heat pump by pushing it too hard and then claiming on the long warranties they supply, also the heat pump by be over working and outside of its efficient band. If you wish to be cynical, one could say they are losing potential sales of more heat pumps.

In our last house, we did have a second heat pump for our bedroom, it was poorly insulated, with lots of glass and 3 exterior walls, so cold and damp in winter and hot in summer. Our present house, has good insulation, double glazing and is generally comfortable, though the main bedroom did need extra heat in winter. The first thought was to fit another heat pump in the bedroom ( a small oilfilled heater would be enough) or risk a heat transfer system from the adjacent living area. The heat pump in the living space is probably over sized for its work load and has never really struggled. I found on the internet that a few brave souls had invested in a transfer system with heat pumps and were generally pleased. I just needed a one to one system, i.e. one inlet and one outlet (you can get multiple outlet units for more rooms).

I bought a HT01 kit from http://airflo.co.nz for $250 with a slight postage surcharge for my rural address. There are plenty of other options available, Mitre 10 and Bunning sell various kits. The system arrived within a week and it took me about 2 hours to install (I had an electrical socket in the loft so that part was easy). When running, the fan makes a very low droning noise and I am sure it would not stop you sleeping, but I did not install the outlet directly into the bedroom, but into the en-suite instead. Health warning: if you do not have an extractor fan in your bathroom the nasty smells and condensation are going to end up in your bedroom. The reason I chose the en-suite is that it tends to be a bit damp and never gets any sun, so positive air movement is bound to be an improvement. Another destination for the outlet is in your wardrobe, this will mask any fan noise and give an airflow around your clothes.

The verdict

Yes it worked well, the bedroom was 2 to 3 degrees cooler than the living area, which is how it should be. I will find out in summer if I can use the transfer system for cooling the bedroom as well. Update: I never found the need to cool down the bedroom!

Fit an isolating switch near the supplied thermostat

Back Draught Shutter ( to stop the back draught from a shower vent)

Back-draught shutter (see the self tapper on the left)

I mentioned earlier that the on-suites can be cold. I had also found on cold windy (Southern winds) nights our lounge struggled to keep warm, but never worked it out. The reason was a howling gale coming back through the extraction fan vent above the showers. I found that out when changing the lamp on the vent when the wind was blowing, I had never noticed before, when in the shower the extractor is on and when not using the shower, the cubicle door is closed and I never felt the draught. The solution is easy, an inline back-draught shutter (they can be called by other names). Non of the usual suspects seemed to stock them or under stood what I was talking about. I ordered two from Plumbing World and was charged $60 each!!!. I should have checked the price before ordering, believe me you can them cheaper. The shutter I got was for putting in line with the flaps horizontal, that was no good for me, and have fitted them directly onto the extract vent above the shower. One problem was, one vent flipped open to far and would not close, so a small mod. as in the photo. A self tapper is fitted above the hinge to restrict the flaps to 90 degrees, this solves the issue and you get a satisfying two clunks from the flaps closing when switching off the fan.

HRV style ventilation from the loft (roof space)

Our house had a Weiss two outlet ventilation system installed. The system failed about a year after we moved in, and upon enquiring, found out that our system was obsolete and only the ducting and vents were reusable. It was going to cost $700 to get it working again. When working the system did give winter heat if the sun was shining and did ventilate the house, but we did not suffer with damp etc. and it was a lot of money just for a bit of heating during the day.

The fan and adjacent control box were duly extracted to my work bench. I found the control box was up the spout, but the fan worked fine. So with some parallel thinking, I bought a change over room thermostat from RS and mounted it were the control box had been, then ran a three core cable to the hall way controller.

I now have a two gang light switch in the hall connected to the stat. in the loft which controls the fan. One switch enables the fan to run if the loft temp. is above 26 degrees C and brings in warm air. The other switch is to enable the fan to operate if the loft temp. is below 26 and bring in cooler air in the summer evenings (I have not tried this mode yet, as we are still in spring).

The above system seems to work fine, but if you think about it, any fan with a ducted vent into a corridor or room ceiling would work just as well. The inlet will need filtering to stop dust. The ducting does not need to be insulated, because its in the same temp. space. One could use a bit of 100mm plastic down pipe with an extract fan (now a intake fan) mounted on top of it, or the flexible duct supplied with bathroom fans.

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