Heat Pump Emergency Setting Myth

[92saturnsl2]

It's that time of year again-- the time of year that we get a friendly reminder from our neighbor to set our thermostat to Emergency Heat because of the "bitter" cold weather we're having. I'm always at work when he stops by so I never have the chance to ask him why he wants to spend a boatload more money on heating his home than he needs to. My wife instead politely tells him, yes, thanks for letting us know.

How does this myth keep getting perpetuated? I've overheard folks at work tell others the same thing "better make sure you set your heat pump to emergency!" It's like the cool thing to do when it gets "super" cold. Sure, I realize heat pumps are less efficient in colder weather for obvious reasons, but it will never (at our temps) be as inefficient as electric grid heat-- most modern heat pumps have a COP of >1 down to -25F or so. Thermostats already use auxiliary electric heat (or gas/oil if equipped) to supplement the heat pump when it can't maintain the set temperature in a given amount of time. Let the system do its job.

Our heat pump does just fine down to low teens and single digits-- at or below those temps it'll run nearly 100% duty cycle (long as it can, with breaks for deicing/defrost cycle) but even at that rate it's still saving money vs reverting your whole system into an electric furnace (emergency heat setting).

Anyone else keep hearing this advice?

 

[Linctex]

I think that started with older non-programmable thermostats...

My mom and dad's first heat pump in the late 70's did SQUAT when it was -35*F outside.
You had to use "emergency heat" if you wanted ANY heat.

New systems are FAR better... but old wive's tales last longer than technology changes.

 

[bullwinkle]

Sorry, I was too busy shoveling wood into my wood stove like a 19th Century steam engine! I'm assuming your heat pump starts the 2nd stage automatically? A coworker of mine has a recently installed heat pump system, he claims it has saved him a fortune in heating oil (he has no nat. gas).

 

[92saturnsl2]

Ours has automatic supplemental heat, pretty sure most modern heat pumps (in colder climates) have automatic 2nd stage. That said, there's probably many older systems that lack it-- which explains how the myth started.

 

[SZR48207]

The one in my home is dual heat (HP/Gas), but it must be programmed to not run in HP mode below 40*F outside. The dang thing will still kick on and try to extract heat before it gives up and switches on the NG burner instead.

It'd be nice to upgrade the entire thing to a fancy Mitsubishi system with a high SEER rating. I've heard the advanced ones can extract heat at ridiculously low temps.

 

[Rand]

Originally Posted by Linctex
I think that started with older non-programmable thermostats...

My mom and dad's first heat pump in the late 70's did SQUAT when it was -35*F outside.
You had to use "emergency heat" if you wanted ANY heat.

New systems are FAR better... but old wive's tales last longer than technology changes.


did you mean -35f or less than 35f

because the new ones barely do anything at -35f.. so less than 35f would make more sense.

 

[Snagglefoot]

Describe to me what that 2nd stage is. My system has a heat pump for the shoulder seasons but reverts to the propane fired boiler with a water to air heat exchanger as the " emergency setting". It's just semantics in my case; there's no emergency , it's just too cold to use the heat pump.

 

[Gebo]

My 88 year old Mom uses Emergency Heat to get warm air coming out of her ducts. Her Emergency Heat is Propane.

 

[CDX825]

Depends on the heat pump you have. Used to be we set the lock out for 30 degrees. The newer higher seer units can go lower and still put out heat but the lower seer units start to struggle when it gets below 25.

I still see a lot of thermostats in the field where you have to manually switch from Heat to Aux Heat or emergency heat. Your neighbor might still have one.

 

[92saturnsl2]

Originally Posted by Snagglefoot
Describe to me what that 2nd stage is. My system has a heat pump for the shoulder seasons but reverts to the propane fired boiler with a water to air heat exchanger as the " emergency setting". It's just semantics in my case; there's no emergency , it's just too cold to use the heat pump.


The second stage is simply an auxiliary source of heat for the heat pump. With a heat pump / gas furnace (or boiler) hybrid, it can be supplemental heat, but in most cases the thermostat is typically programmed to transfer over soley to the gas heat source when the efficiency of the gas unit surpasses that of the heat pump. This can be 40 degrees or so, but depends on efficiency of gas heat source and numerous other variables.

In milder climates like mine, the "second stage" (if we're calling it that) is an electric resistive element, which is wildly inefficient, thus you'd never want to depend on it entirely. Even though it's an energy hog, It works good as a supplemental source of heat for the heat pump because the assumption is that it will only be used in very cold temperatures, which are infrequent here.

Unlike gas 2nd stage, with electric 2nd stage there is no switchover temperature where the second stage heat becomes more efficient (technically there is, but that temp is much lower than any temps we'd ever experience here). Therefore the 2nd stage should be used as supplemental heat ONLY unless you like throwing money away by using the electric heat element to heat the whole house. In other words, the heat pump is still extracting all the heat it can, the 2nd stage only kicks to add more heat in if the thermostat notices that the heat pump is unable to heat the house to the desired temperature in a programmed period of time.

Switching the thermostat to emergency heat tells the heat pump to shut off completely and 100% of the heating output is done by the electric heating elements, a costly endeavor. In the case of gas, there actually is cost savings by using 2nd stage at lower temps where gas is more efficient. Pretty sure the name "emergency heat" comes from the ability to use it as a backup in case the heat pump ever fails.

 

[92saturnsl2]

Originally Posted by CDX825
I still see a lot of thermostats in the field where you have to manually switch from Heat to Aux Heat or emergency heat. Your neighbor might still have one.


All the houses on our road were built in 2008, he has the same unit as mine.

 

[dlundblad]

I did this with mine.

We have a gas furnace and a heat pump. The thermostat is supposed to turn off our heat pump at 32*F and turn on the furnace. I am guessing the temperature sensor is somewhere in the heat pump itself because it can be mid teens and sunny outside, but the system will read an outside temp of mid 40's or so thus running the heat pump when it shouldn't.

I noticed this a few weeks ago so we'll see how the power bill changes next month.

___

Originally Posted by 92saturnsl2
it will never (at our temps) be as inefficient as electric grid heat


This I have a hard time believing honestly. What temps are you guys seeing right now?

 

[dnewton3]

Originally Posted by 92saturnsl2
It's that time of year again-- the time of year that we get a friendly reminder from our neighbor to set our thermostat to Emergency Heat because of the "bitter" cold weather we're having.


Simply put, he's a moron and does not understand how his system is designed to work.
He's the same type person that believes if he's hot inside the house, it will get colder "faster" by turning the thermostat down some more.
He's the same type person that believes pushing the floor button in the elevator multiple times makes it go faster.
He's the same type person ...

 

[JLTD]

Originally Posted by dnewton3
Originally Posted by 92saturnsl2
It's that time of year again-- the time of year that we get a friendly reminder from our neighbor to set our thermostat to Emergency Heat because of the "bitter" cold weather we're having.


Simply put, he's a moron and does not understand how his system is designed to work.
He's the same type person that believes if he's hot inside the house, it will get colder "faster" by turning the thermostat down some more.
He's the same type person that believes pushing the floor button in the elevator multiple times makes it go faster.
He's the same type person ...



Nailed it.

Only time you need emergency heat (no matter the way it works) is when your regular heat cannot keep up.

 

[92saturnsl2]

Originally Posted by dlundblad
This I have a hard time believing honestly. What temps are you guys seeing right now?


We've back in the 20's today; the lowest we got down to was 4F.

The COP (coefficient of performance) is a ratio of output power to input power. An electric heating element has a COP of 1 (one unit of energy = 1 unit of heat). A heat pump's COP falls as temperature drops, but for most any modern heat pump to drop below a COP of 1 would require temperatures to be well below 0. The unit I have according to the manual is -25F. Problem is the heat output of a HP drops so considerably at those temps that supplemental heat is required to heat the house effectively. Even though the heat output drops so substantially, the heat that the HP is still able to put out, is more heat per watt than a standard electric furnace would be, until you get to -25, in my case.

A gas furnace has a COP of much greater than 1, so there is absolutely merit in switching from the HP to gas, when outside temperatures are at a level where gas heat is more efficient.

So in no way am I suggesting you can just use the heat pump and all is well-- they just aren't large enough to put out enough heat at very low temperatures. But the heat it IS able to generate, is without a doubt more efficient than switching the whole system to emergency mode and relying solely on forced air through a heating element. If one wants to save money, don't intervene and instead let the system use the HP and only add backup heat as required to maintain the set temperature.