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May 23rd, 2012 | energy saving
you don’t need to leave your heat pump since it’s a waste of energy and your bills could raise up. Consider this site as a great reference when it comes to effective heating approach http://brivis.com.au/blog/whats-efficient-way-heat-home/
This is good, sound advice. Following these suggestions will significantly reduce your electricty bills.
Excellent write-up as always Chris and thanks for helping inform Tasmanians about technology use in Tasmanian conditions. Also appreciate the plug for Sustainable Living Tasmania. Cheers, Corey SLT President
The article was long enough not to add any more, but this issue is so similar to the longstanding and widely held myth that it was more efficient to leave fluorescent tubes on then to keep turning them off. Some people still believe this to this day – despite that myth being debunked by science a long time ago.
That old myth was so widely accepted that entire cities of skyscrapers were left lit up permanently, and for no reason.
The Australian climate office and all similar agencies now give the same advice… if you aren’t using lighting then turn it off.
It is now verified with ample testing that the short burst of energy used to turn on a fluorescent tube is recovered within seconds. Very frequent turning on or off of fluorescent tubes can shorten the tube’s lifespan, so they are not generally used in situations like private toilets where lighting is only needed for a minute or two. Other than that it’s a non issue.
Thank you Chris. At last an authoritative piece that explains everything. We are constantly coming up against the same arguments on our round of home assessments and it is hard work getting people to accept the logic of turning off the heat pump overnight when they were told otherwise by “experts”!
What about the risk of the water freezing outside in the pipes? That’s the reason I’ve heard for leaving heat pumps on in winter.
I don’t know where you live, but if you live in Antarctic-like conditions such issues can come to the fore. That’s not the case for most places in Tasmania.
Note that heat pumps are not connected to your water supply. When freezing happens it’s to do with water that condenses from the air not in pipes. Heat pumps operate with a closed loop and the pipes conjoining the compressor and the inside heater unit are always well lagged.
If, in your location, you experience winter overnight temperatures well below zero then there is a case for leaving the unit ticking over all night, but keep that option for really extreme conditions. In Tasmania that may mean whilst we have a really cold snowy front blowing over. Most of our winter nights are not in that category. In Hobart I run a heat pump all winter without any overnight use and it easily warms up the living area when we set the timer to come on, even on cold nights.
Great article with a lot of information but a few more pictures of how a heat pump actually works would be great. A great site I found on the topic was http://www.heatpumpguide.com for anyone else looking for more information, maybe you can add it to your article chris?
We’re a group of volunteers and starting a new scheme
in our community. Your web site offered us with valuable information to work on. You’ve done an impressive job
and our entire community will be grateful to you.
i am in Canada and I have a heat pump it works good thanks for advisce
I am a bit confused. If the temperature is above the heatpump setting, the compressor shuts off correct? Like and AC in the summer. Leaving your AC on at a temp of 72, when the house gets to 71 or so, the outside AC shuts off. My heatpump works the same. If I have heat set at 72, and temp gets to 73, the heat pump / compressor shuts off. Do some units run 24×7 unless you shut them to off position? I thought that is what the thermostat does.
You are partly correct. The compressor will, in time shut down, but it still needs to remain active and stop and start depending on room temperature.
what I did with this article is to get people to use their heat pump intelligently, rather than take the suppliers direction to just leave it on permanently. This is ok for convenience but not for optimisation of energy saving.
As the article describes, how you manage your heat pump depends partly on the level of insulation of your home, its thermal mass and other factors.
Another area (not explored fully in the article) is the potential to optimise heat transfer when outside temperature is fairly high (mainly in afternoons) but getting best from the unit in these circumstances can only really be done well if the home is very well insulated and has significant thermal mass.
In accordance with this, a heat pump operated hot water system is best timed to only run during afternoons and off when ambient outside temperature hardly has any heat in it to extract.
Thank you for your comments Chris. I am a little unsure / confused yet 🙂 If I use my programmable thermostat and at night the thermostat temp is set to 60, but the room temperature drops from 72 to 62, then the compressor would not be running during this time correct? The electricity use would be $0 during this time? Or does the compressor still use some electricity and runs during this “Off Cycle” mode?
I do have another question regarding my heatpump if you can give advice. When I had the units installed, I had a 92% efficient natural gas furnace and the high seer heatpump. At first the installer had just gas furnace and AC, I asked how much more for a heatpump, he said $400. But that I would be wasting my money. Who knows what natural gas prices were doing and at that time they were 3X what they are now. I pay about .47 per therm now, and I have been using heat in the EMER mode so it uses the natural gas furnace and not the heatpump. I have spray foam insulation which seems well. My gas bills for this furnace, my second old 80% unit, stove, grill, and water heater runs about $40 during a normal winter month, and $60 if really cold. LOL, I am in Atlanta, so it never gets really cold like in WI. I keep the house comfortable 72-74 during day, and about 65 at night. I will probably test again, but with gas prices low, I thought it is cheaper to run the EMER mode using gas rather than the heatpump. Elect rate is .078 per KWH. Any suggestions, or probably does not make much difference.
I was looking to get more info about your location then I realized we are on opposite sides of the world. I do not know much about Tasmania. My wife has been close, but we do hope to visit as soon as I am not required to do that working thing 🙂
I live in virginia. I have a gas furnace for first two floors and heat pump for next two floor. This is the combination. I though HP are supposed to reduced utility bill but something opposite happen. My electricity bill came around 2 times that of Gas bill. Gas is also used for heating water.
I was worried why this happened called the electrician to check the HP. He filled more freon gas as he said that was less and heating was not happening properly.
Query: You are saying not to run it all night and i was advised to keep it running all time. Eg: When i was left home to work,i kept it at 65 F, and when i returned from office i made it 70F, programmable thermostat. Since there is a diff of 5, the HP is kicking in the AUX heat, i,e it is running completely on electricity full throttle till it reaches 70F. Similarly at night i was keeping it at 65 and using a room heater and in morning temp to 70 F. Again the Aux Heat kicks in.
So this is perhaps leading to very high electricity bill…
Please advise your thoughts on this.
Is there a way of stopping my heat pump from sending out cool air once the room temperature is reached? It would feel so much better if it simply shut off instead and then came on again when the temperature drops. We have a Samsung Whisper. Your response will be greatly appreciated.
Hi Pam, I think there’s little control over that.
The higher quality heat pumps, such as Daikin, don’t do this.
There are many off-the-shelf cheaper brands on the market and many of those do not operate very well but once isntalled you are stuck with them. I would have thought that Samsung would be not at the bottom of the range though – most of their products are reasonable.
Generally the floor based heat pumps that are primarily designed as heat pumps are better engineered. Many air conditioners sold in Australia are primarily built for cooling, but will also go into reverse cycle when you need to heat.
I think it is worth noting that this article may only be applicable to those that live down-under. In the US there appear to be some major differences, including that compressors usually turn off when the unit is not running (see paragraph titled “If your home is well insulated”).
In the United States, most heat pumps are installed with a backup electrical strip heater (http://www.energyvanguard.com/blog-building-science-HERS-BPI/bid/35547/How-NOT-to-Use-Your-Heat-Pump-Thermostat) which uses about 3 times as much energy as a heat pump when heating your home.
In the US, the reason installers tell folks to leave their heat pumps on all day and night in the winter is that if you have electrical strip heating as a backup to your heat pump, it will be used to heat your home (at 3 times the cost!) whenever your thermostat setting is more than 2 degrees above the current temperature inside the house. That is, when you bump your thermostat up 10 degrees in the morning or in the afternoon to heat your home, most thermostats in the US will activate the electrical strip heaters.
There are some programmable thermostats that will ‘learn’ your heat pump and will not use the strip heaters unless the heat pump cannot keep up, but most homes do not have this type of thermostat. My thermostat calls this “recovery mode”.
If you have a heat pump backed up by electrical strip heaters and you have a non-programmable thermostat, you can avoid extra costs by turning up your thermostat setting one degree at a time (wait for the unit to shut off and turn it up another degree).
Hope this helps some of the Yankees coming to this page!
It’s true there are few places in Australia that have as severe Winter nights as you do in the Unites States and Canada. The purpose of the above article was to try to get people to use their heat pump intelligently, rather than just switch it on and leave it. Convenience may be your only yardstick, in which case there’s no need to do anything. Where people like to save money, reduce wear and tear on the machine or wish to reduce wasted energy, then it pays to use the machine dynamically.
Okay, so what we tend to do is keep an eye on the weather forecast.
In our case we perhaps use the heat pump during 6 months of the year. For most of that period the night time temperature stays above the level where the heating strip (or reverse cycle) switches on to prevent the machine freezing. This would be the case in most locations in both Australia and the US. So running the machine all the time every day, to cater for those nights when temperatures run are close to zero is not the best way to manage the machine generally. We keep en eye on the forecast and opt to run the machine at a low temperature setting only during those clear sky very cold nights.
If you live in a truly freezing situation where your night time temperature is nearly always around freezing then it is arguable that an (outside compressor) heat pump is not the most efficient way to heat your home. If that’s what you are stuck with, then what you say may be true, it may be better to generally leave it on during the night on a low setting, then boost it up in the morning. The better brands will enable you to set it on, say, 12 degrees (Celsius) during the night, but some don’t have this facility. The rub is that keeping your home toasty warm all night loses unnecessary heat, so it’s still better to manage your heat pump.
I realize that many people have busy lives and don’t necessarily worry too much about power wastage, so leaving the machine on permanently is an easy solution. Meanwhile, the manufacturers find it too hard to educate their customers, aware that each home and its owners have their own characteristics, so the easy way out for them is to give out a one-size-fits-all message.
Many thanks JB for taking the time to relay your thoughts on this.
Hi GMS (further above),
It’s hard to diagnose at a distance. Sounds like your system may be faulty. Your auxiliary heating system is kicking in rather than saving energy? It’s probably true that if you have your thermostat set and an auxiliary heating system automatically kicks in when the heat pump is off, then the above advice may not be relevant to your set up. The advice in this article is for stand-alone heat pumps.
Im a little confused about heat pump. When it warm during the day around 65 and the temperature drops to 47 at night it seem my heat pump or unit fan in my attic constantly run. What should i put my thermostat on at night
Hi T Bee,
This depends on your lifestyle and who occupies your home. If you are off to work in the morning and your home is empty during the day then it’s probably best to turn your heat pump off. This applies to many households. It’s not efficient to heat your home all night just for the 30 minute that you spend at breakfast… and you don’t live in a very cold place.
During most of the year I turn ours off and time it to turn on about 30 minutes before arising.
If your home is occupied during the day and your family expects the house to be always warm, then on colder nights leave it on at night but set the temperature very low, just to keep the chill off the air. This will enable the heat pump to warm the living space a bit faster. But you will use more power.
Every home situation is different. I can’t give a formula that applies to everyone. The main thing is to use your heat pump intelligently and (if you wish to save energy and money) don’t just leave it running without thinking.
Thanks for your advice about heat pumps. I assumed that leaving the pump on would be fine. I didn’t even consider that the noise would be bad for my neighbors. If it saves money then I’m all for it. However, is there an outside temperature that would make it better to leave it on?
Good question, Ian.
Most heat pumps have an auxiliary heating system that cuts in when temperatures are too low. This is to help stop the heat pump from icing up. But also recognising that heat pumps simply can get much heat out of very cold air. If you keep an eye on the weather forecast and the night time forecast looks like being 2 degrees (celsius) or below then it may pay to put the heat ump onto a low temperature setting (like 10 degrees) so that it maintains some warmth but doesn’t have to work too hard. when you get up in the morning then you can turn it up and it will cope a bit better than having to warm up a very cold space, when it is too cold to do that quickly.
In these circumstances I still do turn it off at night and set the timer (on a low temperature setting) for an hour before we get up and thus allow the heat pump plenty of time to to build up the temperature without too much load.
It surprises me how many people never learn to set the timer, yet this is the best device for managing your heat pump well.
I have never heard such a ridiculous suggestion. Heating systems are not made to be turned on and off like this. They are meant to set on a comfortable temperature and be left alone to regulate it. Certainly, you could lower that temperature at night, perhaps by means of a programmable thermostat, but you most assuredly should NOT simply turn the system off. You are going to use a significantly higher amount of energy to return your home to a comfortable setting after it has sat for a number of hours. You also have to remember that your home and the furnishings absorb and return heat to the room as well, so when you allow a room to get “cold”…the walls and the furnishings are also cold, and they too have to have their temperature raised. Otherwise, even your walls will radiate a lower temperature back into the space until they warm up again. It’s a lot more than just raising the temperature of the air in the room. I think whoever wrote this was on something at the time.
Thanks Lee, but this is not a ‘suggestion’ it’s simply a way to manage an appliance to obtain best efficiency. Extracting heat from ambient air is much more efficient at higher temperatures than at low temperatures. At very low temperatures it’s not a very efficient mechanism at all.
For people who own buildings that have very high thermal mass, for instance, it is best to use the heat of the day to warm it up and rely on that heat being held over during the night in the thermal mass – much as we do when we heat hot water in a cylinder and have a hot shower in the morning.
I’ve been managing our home heat pump intelligently for the past 15 years and it hasn’t missed a beat, has low maintenance and our home is comfortable.
For people who don’t want to think about it, they can leave the heat pump on 24/7 and it will work. But if they wish to get best efficiency then they should try to understand the technology and use it to get optimum performance.
The advice may not reflect best practice on inverter heat pump system made by Japanese manufacturers.
Inverter heat pump system working at partial load provide substantially higher COP than if it is to run at full capacity. For comparison, (can I name it?) one inverter heat pump system deliver 27000 Btu/h (divide by 3.41 to obtain kW/h heat output rating) with 3.4 COP @ -12 C, but a measly 2.3 COP if it were to run at full capacity @ 54000 Btu/h.
For a house that has a 27000 Btu/h heat load @ -12C, the total heat loss over a 8 hr night would be slightly less than 216000 Btu (not accounting the effect of reduced heat loss when the temperature drops – let’s assume a house with high thermal mass, in other words, concrete house.)
Now if one were to turn off the heat pump and coast at night, it would take the heat pump running at full capacity @ 2.3 COP for 4 hrs to recover heat loss during the night. The total energy consumption would be 4*((54/3.41) / 2.3) = 27.5 kWh.
Contrast to running the heat pump all night @ 27000 Btu/h – 8*((27/3.41)/3.4) = 18.6 kWh. You can form your own conclusion.
Hi Heat Pump User,
May I ask, do you apply this all year around?
If your ambient night time temperature is (say) +6 degrees?
Thanks for the feedback. I’ve prepared this advisory for average conditions.
This is a local website and in this area our night time temperature very rarely drops below zero degrees. We never, ever experience -12 degrees C.
In an area that experiences -12 degrees C repeatedly through the year, I would recommend against using ambient air heat pumps for heating because the burden on them is too great and their efficiency is markedly reduced.
Nor do I recommend a blanket rule. I recommend the householders simply uses their brains and take note of the forecast temperatures. Ten below zero nights are not the same as ten above zero nights.
We need to use our heat pump for about half the year. Half a dozen nights during mid Winter are close to zero degrees C. Most nights sit above that level, maybe 5 or 6 degrees.
Rewarming the living space in our case typically takes 30 minutes. If it took four hours (as in your case) then I would recommend running it at a low level overnight (as I’ve already stated in other comments here). But I would also not recommend the installation of a heat pump if those conditions are experienced regularly.
I provided the above advisory to educate people to use their heat pump intelligently rather than turning it on and forgetting it. But I would be the first to agree, an heat pump is not like a resistance heater that is turned on and off for immediate and short term heat gain. That’s not intelligent either.
Thank you for your reply. Use of heat pump system in mild climate (in fact, all climate) can take advantage of inverter driven heat pump system which can modulate its output capacity based on actual heating/cooling load.
For some of the most popular models being installed here in the united states, heat pump COP under partial load condition at ~8C can exceed 5. The argument goes the same way as my previous reply in that an inverter driven heat pump enjoys substantially higher COP running at partial load than running at full load. As long as the system is sized correctly for the heating load / cooling load and enough consideration are given to load vs minimum capacity output, one can indeed save energy by leaving a heat pump on.
This is valid up until the point when the heating load / cooling load goes below the minimum modulating capacity, where the compressor cycling on and off can adversely affect the integrated COP by quite a substantial margin. Interested readers should definitely check out laboratory test released recently (within the past couple years) on these latest heat pump system.
Additional info on heat pump use in cold climate:
There are heat pump systems developed specifically for use in cold climate region. These system can deliver the rated capacity down to -15C/-18C, and continues to provide heat at reduced capacity down to -23C.
However, as you noted, the COP of the system indeed does take quite a hit operating under these conditions. Even the best inverter driven heat pump today when subjected to these conditions can barely maintain a COP a little over 2. However, these systems still make sense for regions that has no access to natural gas. Afterall a COP of 2 is still significantly more efficient than electric resistance heat (a COP of 1).
An additional piece of advice for energy conscious owners of heat pumps who turn off their heat pump in Summer…. please note that most heat pumps have a live circuit that operates even when the heat pump is switched off. This can typically be about 15 watts.
Thus, if you turn off your heat pump at the normal switch (on the machine or on the remote) this amount of wasted energy will accumulate all Summer long and become a sizeable amount. Therefore, if turning off the machine for extended periods (weeks of months) it is good to turn off the machine at the main switch at the power meter.
For normal operation, my local energy adviser who runs workshops on heat pump management advises to turn off the heat pump during Winter nights except when conditions may be very cold. I’ve adopted this advice for the past ten years and our machine not only uses less energy than most households, there is a lower demand on the compressor unit and so I’ve had minimal need to service the machine.
But I agree that anyone living in really extreme environments where the heat pump is being used to extract air from sub zero conditions the machine’s operating efficiency would be very low if it had to try to warm up your living space quickly. In fact they aren’t designed to work at that level.
For people who get out of bed and throw down some breakfast and then spend the rest of the day at work it would be more sensible to use an auxiliary heater at breakfast time rather than keep their heating system pumping all night long just for that half hour.
When auditing homes we very quickly get to understand that everybody’s home architecture, climate and living arrangements are different, so I wouldn’t apply a blanket rule for all. But for every conscious householders it’s best to understand that you do have flexibility if you are in touch with your energy supply, rather than use it mindlessly, and in this way you can get the best performance from it.
One thing that surprises me is the number of people who own and operate a heat pump but who never learn how to use the timer. The timer is provided in order to manage the unit optimally. In our case, (depending on the night time temperature) we set the timer to turn on the machine about half an hour before we normally arise and we then get up to a pleasantly warm room. This works perfectly for us because we limit the area that is heated and have good insulation. These are other parameters that need attention in an energy wise household.
I live in Ma, U.S. I have a Diakin heat pump for a/c and heat we live in 525 sq ft apt well insulated the unit is new we don’t live there in the winter we have the temp set at 54f my son says the heat pump runs all the time even when the room temp is 65?? Even in the summer the unit ran a lot to get the temp down to the set point the unit is a 24,000 btu what do you think thanks
I don’t try to tell people what to do, every person has their own needs. People may want to moderate how they use their heat pump for personal cost reasons or if they have a concern for environment. Basically, as this article has tried to describe. If you set a temperature and leave it on all the time and never what to experience any discomfort of cold or heat then the heat pump will service your needs, but it can do the same if you manage it a little. I guess it is a bit like your car (if you have one) you can get by now knowing how the engine works and leave everything up to your mechanic. Or if you know a little bit about engines then you may drive differently and so forth. My overall advice to anybody is to use your that pump wet intelligence rather than just leave it permanently on. That said, a heat pump is not like a bar radiator. You wouldn’t use it just to walk into a room and turn it on and expect to warm up in a few minutes. Your that pump will have a timer. Many people don’t use the timer ever and never learn how to use it. Using the timer is a good way to get best performance with little trouble.
Thank you for all of the insight about heat pumps, I wasn’t aware of how potentially efficient they can actually be! As you say, it reduces the amount of energy that is actually being used because it’s pulling from already existing heat. However, you talk about how this is only the case if other components to your house and the actual pump are well maintained. I’ll make sure that I get the pump regularly checked at and that my home is properly insulated and maintained as well. Thank you so much for the insight!
u can set a timer that assigned for off after use.
Thank you for the information about nighttime use of heat pumps. I have just had a new heat pump installed to replace our old one which had died after 17 yrs use. The new one is a 7wt and a bit more than the old one but it doesn’t seem to be putting out the heat that the old one did and I am running it on 24deg c in order to obtain the heat in the room that I would get with the old one running on 22 deg c. Do you think this may be a fault that needs attention or is this how they operate these days? I would appreciate your thoughts.
That’s really hard to say from a distance Vivien. If the fan on the new one is running stronger the moving air can make temperature feel colder, so you may need to turn the fan down a bit.
There’s a lot of difference in the quality of heat pumps. Three brands in Australia are mainly recommended, many of the other off-the-shelf cheaper ones don’t perform as efficiently.
If you have a reputable brand and it doesn’t seem to be performing as expected I would get the installers back. But give it a good run first.
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