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  #1  
Old 01-18-2005, 11:37 AM
larsenmtl larsenmtl is offline
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Heat Pump - Emergency Heat

With the recent artic cold embracing the east and a very crappy heat pump in my town house, things have been seriously frigid. This morning the thermostat said it was 60 degrees inside the living room, which means it dropped 6 degrees overnight. The heat pump is running continously but it just can't keep up.

Anyway, my brother-in-law said that if I just flip the system over to emergency heat it'll warm the house back up (at the expense of electric). Is this true? Am I damaging the system doing this?

Usually we'd just tought it out, but our 10-week-old baby makes us worry.

Update - My wife just called me and said that even with the EM Heat running since 9 AM, the thermostat is still reading 60.
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  #2  
Old 01-18-2005, 11:48 AM
Q.E.D. Q.E.D. is offline
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The emergency heat is a smallish ancillary (usually electric) heater, the purpose of which is merely to keep the house from freezing inside to the point where the pipes burst. You won't damage the heat pump by running it, but it's not likely to do much good. Clearly, your heat pump wasn't sized for the current weather conditions. If this is a frequent occurrence, you might want to look into upgrading to a higher-capacity unit.
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  #3  
Old 01-18-2005, 12:03 PM
kanicbird kanicbird is offline
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Heat pumps get less efficent as the outside temps fall, this is due to the HP taking heat from outside and pumping it inside. When temps are below freezing then the HP outside coil will start freezing up which reduces efficency of the H.P. So most HP's have a resistance electrical heat seting, which just turns your heappump into a big space heater. I assume your emergency setting overrides this and puts it into resistance heat mode all the time.

If so, no it won't hurt it, and it was most likely running in that mode anyway.
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  #4  
Old 01-18-2005, 12:11 PM
SavageNarce SavageNarce is offline
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Other possibility: your heat pump is like a refrigerator, except you are connected to the output side (the coils on the back of the fridge). If it is running continuously, then it might need to get checked out, especially the refrigerant (freon) level. There might be a leak in the system, and without enough refrigerant to work with, the compressor would run constantly without any appreciable effect.
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  #5  
Old 01-18-2005, 12:12 PM
Merkwurdigliebe Merkwurdigliebe is offline
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I'll give you my reccomendation.....





I went to Wal-Mart and purchased this little heater that looks like a radiator that is filled with oil. That sucker can heat a pretty damn big area. If things are getting really uncomfortable its really cool, because unlike a lot of space heaters it isn't so directional, and it is cheap (like 30 dollars), plus just manages to warm up a room fairly quickly.

Luckly I live in an apartment complex where electricity is included in the rent and isn't based on usage! So I pretty much take advantage and keep my room as toasty as I want it. But seriously. This thing will make a room downright sweltering after an hour, I haven't tried it in big open areas, but I imagine if you turned it up all the way, it would at least augment the heater in your house. Plus it is cold here. It was around 27 degrees today at about 10 AM, so its not because it isn't cold here.
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  #6  
Old 01-18-2005, 12:18 PM
Q.E.D. Q.E.D. is offline
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Quote:
Originally Posted by kanicbird
HWhen temps are below freezing then the HP outside coil will start freezing up which reduces efficency of the H.P.
Don't some heat pumps have low-wattage resistive evaporator coil defrosters? I seem to recall reading about this someplace, but I'm havign some trouble finding anything definitive online.
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  #7  
Old 01-18-2005, 12:55 PM
GaryM GaryM is online now
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Former heat pump owner checking in.

As stated earlier, when the heat source temp, normally the air but could be ground source in some cases, falls too low the unit can't extract enough heat to warm the house sufficiently.

Heat pumps usually have a two stage thermostat. A temp drop kicks on the heat pump and it heats the house. If it can't keep up and the temp drops some more, usually 2-3 degrees, the electric heating coils stage on and off as required to supply heat. I say stage because my unit had three sets of coils. One would come on and supply heat. If that wasn't enough and the temp stayed low, the second and third set of coils would come on as required.

It wasn't unusual for the unit to run almost all the time if the air temp was in the single or two digit range.

It's possible that you might have a burned out coil or coils. Or it could be a thermostat or sequencing switch failure. With the heating coils activated, the air from your vents should be significantly warmer than when they are not activated.

Call a HVAC guy to check it out.
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  #8  
Old 01-18-2005, 01:05 PM
AWB AWB is offline
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Quote:
Originally Posted by Q.E.D.
Don't some heat pumps have low-wattage resistive evaporator coil defrosters? I seem to recall reading about this someplace, but I'm havign some trouble finding anything definitive online.
We recently replaced our HP because the defrost mode didn't work. (The outside coils got coated with ice overnight.) What we were told is that when the HP detects that it's getting iced up, it runs in cooling mode (like when we used it in the summer). This transfers heat from inside to out to defrost the coils. Then it goes back to heating mode. (Our old HP didn't work for summer cooling, so lack of this function frosted up our coils real quick. I spent about a week of nights with my wife's hair dryers and a heat sealing gun trying to expose enough coils to get us through the night until we could get the new HP.)
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  #9  
Old 01-18-2005, 01:28 PM
larsenmtl larsenmtl is offline
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Quote:
Originally Posted by GaryM
Call a HVAC guy to check it out.
Like a good boy, I actually had the unit inspected and serviced at the beginning of the winter. Everything checked out ok, then. Of course, with the EM heat on the air doesn't feel significanly warmer.

I'm curious that even with the auxillary emergency heat going, the unit still can't keep up. It's been really cold in Baltimore, something like 12 degrees last night and 20 degrees now.

I'm calling my home owners association now to see about having gas run from the street.

Thanks all.
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  #10  
Old 01-18-2005, 02:35 PM
spingears spingears is offline
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Quote:
Originally Posted by larsenmtl
Like a good boy, I actually had the unit inspected and serviced at the beginning of the winter. Everything checked out ok, then. Of course, with the EM heat on the air doesn't feel significanly warmer.I'm curious that even with the auxillary emergency heat going, the unit still can't keep up. It's been really cold in Baltimore, something like 12 degrees last night and 20 degrees now.I'm calling my home owners association now to see about having gas run from the street.Thanks all.
A heat pump does nothing with 12 or even 20 deg outside.

Your heat pump system is seriously deficient in original sizing/selection or it is defective.
There should be enough electric heat to keep the townhouse up to at least 68 deg. when the outside temp is down to the design value for MD.

The only time my heat pump systed didn/t/couldn/t keep up was when we had a very cold time for a few days of -20 deg. in TN. Used a large kerosene heater in one room, shut it off at bedtime and piled up the blankets!
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  #11  
Old 01-18-2005, 02:43 PM
Brutus Brutus is offline
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For the sake of the unitiated (me), what is a 'heat pump'? My house has a shiny new furnace, replete with fans and humidifiers and dehumidifiers and a bunch of captivating blue flames that look like candy. Where does a heat pump fit into that?
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  #12  
Old 01-18-2005, 03:11 PM
gotpasswords gotpasswords is offline
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Brutus - it doesn't. A heat pump is (in really basic terms) an air conditioner that can be switched to run in reverse - instead of pulling heat out of the house, in the winter, it pulls heat out of the outside air and moved it inside.

They're good in temperate climates - down to about 20 degrees or so, there's still a useful amount of heat to be squeezed out and used to heat a home. Decent in say, San Francisco, but not so good in Minnesota.

What you've got with the blue flames is a traditional gas furnace and maybe a standard air conditioner.
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  #13  
Old 01-18-2005, 03:48 PM
BubbaDog BubbaDog is offline
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Quote:
Originally Posted by gotpasswords
They're good in temperate climates - down to about 20 degrees or so, there's still a useful amount of heat to be squeezed out and used to heat a home. Decent in say, San Francisco, but not so good in Minnesota.
Actually, they can be designed to work in just about any climate. The big problem comes from the fact that the HP also acts as a summer air conditioner. If the HP is designed to pull heat a out of a very cold climate it will usually be too large for summer cooling. Oversizing an airconditioner can make the house uncomfortable in that it chills so quickly that it won't dry humid air. So instead of a dry cool home you have a cool musty one.

Some HPs use two-stage compressors so that the winter compressor can do more work than the summer.

In any case, it sounds like either the emergency (resistive) heating isn't working or the pump is way undersized. In either case it may be best to call in the technician.
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  #14  
Old 01-18-2005, 05:38 PM
Gorsnak Gorsnak is offline
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Quote:
Originally Posted by BubbaDog
Actually, they can be designed to work in just about any climate.
You aren't kidding. The current big thing in heating in these parts (Saskatchewan, land of -40) is "geothermal", which entails sinking several thousand feet of hose into the ground below the frost line and using it as a thermal mass on the other end of a two-way heat pump, giving you central heating and a/c both, all for far less energy than the usual gas furnace. A large senior's complex in town is having a system put in to the tune of a million bucks, but they expect it to pay for itself in energy savings in 8 years. More and more new homes are being built with it as well, though it costs rather more up front than a conventional unit.
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  #15  
Old 01-18-2005, 07:32 PM
beltbuckle beltbuckle is offline
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Heat pump owner checking in.

The "Emergency Heat" selection on a heat pump thermostat is a bit a misnomer. In my opinion it should be labeled "Aux. Heat Only", as that is typically what it does.

See, air-source heat pumps, when run in cool environments, don't pull enough heat from the air to heat the house. The thermostat detects when enough heat isn't being supplied, and kick on the aux. heat to meet the temperature requested. This happens periodically depending on the temperature and heat loss of your home.

For instance, right now it is about 28 degrees outside. The heat pump itself seems to do OK most of the time, but some of the time it is kicking on the aux heat (which in my situation is 2 x 20kW electric strips). If it gets colder, it calls on the aux heat even more.

In normal operation when the thermostat calls for the aux heat, it keeps the heat pump running as well, so you are getting some heat from the heat pump, which is supplemented by the aux heat. So both can be running at the same time.

In "Emergency Heat" mode, it just runs the aux heat, and the heat pump shuts off completley. So Emergency Heat mode is just running your aux heat.


There are a couple of situations I could imagine switching into Emergency mode:
  • It is so bitterly cold that your heat pump is pumping almost zero usable heat into the coils in your air handler -- thus it is just wasting electricity operating the heat pump compressor.
  • Something is wrong with your heat pump, and you wish to just use your aux heat to prevent damage to your heat pump.

So if your house can the temperature the thermostat calls for, either in normal or Emergency Heat mode, you have a problem with either the heat pump or the aux heat (which sounds like heat strips in your case). Since it is providing some heat, but you don't notice the air coming out of the registers being notably warmer, my bet is that something is wrong with your aux heat system.
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  #16  
Old 01-18-2005, 07:45 PM
beltbuckle beltbuckle is offline
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Sorry, let me rephrase my last paragraph:

So if your house can not meet the temperature the thermostat calls for, either in normal or Emergency Heat mode, you have one of the following problems:
  1. Heat pump is not operating properly
  2. Aux heat (electric stips in your case) are not operating properly
  3. Your heating system was improperly designed and not capable of providing enough heat to match the heat loss of your house
  4. Your thermostat is not wired properly, and is not calling for aux heat in reality.

If you notice the air from your registers is luke warm when just the heat pump is on, then your heat pump is probably working OK.

If the air is not noticably warmer when the aux heat comes on, then there is likely a problem with your heat strips or thermostat wiring.


To test this, put your thermostat is Emergency Heat mode. Is the air warm? if it is not warm, I think you have found your problem: either the heat strips are not functioning or the thermostat is not wired correctly.
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  #17  
Old 01-18-2005, 07:50 PM
beltbuckle beltbuckle is offline
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Quote:
Originally Posted by Gorsnak
You aren't kidding. The current big thing in heating in these parts (Saskatchewan, land of -40) is "geothermal", which entails sinking several thousand feet of hose into the ground below the frost line and using it as a thermal mass on the other end of a two-way heat pump, giving you central heating and a/c both, all for far less energy than the usual gas furnace. A large senior's complex in town is having a system put in to the tune of a million bucks, but they expect it to pay for itself in energy savings in 8 years. More and more new homes are being built with it as well, though it costs rather more up front than a conventional unit.

This is exactly correct. For those that don't know, there are different kinds of heat pumps
  • air source (cheapest and most common, but don't work well in cold climates)
  • ground source, which consist of coils installed in the ground, pulling the heat from the earth
  • water source - where the coils are run through a well or body of water pulling the heat out of the water
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  #18  
Old 01-19-2005, 05:09 AM
spingears spingears is offline
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An after thought:
Did/have you checked the fuse box?
There is usually a fuse box for the heat pump with a ~ 50 A. main fuse and two ~30 A. fuses for the electirc heater bank.
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  #19  
Old 01-19-2005, 09:06 AM
larsenmtl larsenmtl is offline
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Quote:
Originally Posted by beltbuckle
If the air is not noticably warmer when the aux heat comes on, then there is likely a problem with your heat strips or thermostat wiring.
It is not noticably warmer. It feels exactly the same as when it is off.

Quote:
Originally Posted by spingears
An after thought:
Did/have you checked the fuse box?
There is usually a fuse box for the heat pump with a ~ 50 A. main fuse and two ~30 A. fuses for the electirc heater bank.
This I did check, no tripped fuses.

I have a call in to my local HVAC techs. Thanks all.
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