Why do heat pumps suck ass when it gets below 30 degrees outside?

[SCRUBDASHRUB]

It just blows cold out from the vents; hubby turned off the furnace last night b/c of it. It was cold as a witch's tit in a brass bra this morning. Brr...!!

[short bus president]

1. It's 16 here tonight, and my heat pump's cranking out hot air.

Very expensively, but it's cranking out hot air. ;-)

[Spinzonner]

2. Aint much heat to 'pump' from outside

http://energyoutlet.com/res/heatpump/balancepoint.html

And you seem to have an inordinate knowledge of Wiccan foundation garments

[gristy]

4. A great link

that answers the question. I'm impressed!

[clydefrand]

3. Cold ground; cold air is the way I understand those dudes.

And by golly, it's cold enough to freeze the balls off a brass monkey today here in the good old red state of Virginy...except some people might be blue in these here hills.

[SCRUBDASHRUB]

12. I'm in VA, too.

[No Mandate Here.]

5. Don't go out and look at your electric meter

It is spinning so fast it will be a blur. You are heating with resistance elements. Imagine about three of the burners on an electric stove bright red. Depending upon how big the house is, that's what's heating you right now.

Air to air heat pumps are pretty efficient the rest of the time.

[SlackJawedYokel]

6. Also depends on the type of heat pump

IIRC, there is a more expensive type that has pipes that go deep underground to extract heat from the earth(further down you go the warmer it gets).
Most cheapo heat pumps don't do this but compensate by putting regular old electric heating coils somewhere in the system.
If you're lucky.

A house I lived in didn't even have that and we had to keep the fireplace well fed to keep warm.
Sucked.

Cletus

[48pan]

7. Something about differential temperatures...

between the ground and the air. Up north, heat pumps don't work worth a damn. The air is cold. The ground is cold. The heat pump sucks.

[skygazer]

8. Is it an oil furnace?

If it is, oil can gel in the lines when it gets very cold. I always mixed a 5 gallon can of kerosene into the tank in very cold weather. It thins it - recommended to me by a furnace tech. Put it in, give it a bit, and bleed the lines.

[SCRUBDASHRUB]

14. Electric.

[Sporadicus]

9. Most Heat Pumps Have Electric Heating Elements for Supplemental Heating

when the temperature drops below about 20°F. You may want to get that checked out soon. You won't like it when the electric meter spins like a top when they kick in, but it's better than freezing!

[fairfaxvadem]

10. Most of them are pretty crappy.

At least, around here in Northern Virginia. Every person I know who had one were basically never warm if we had a cold winter. Maybe really new ones are better.

But, they were really popular to install during the 80s in particular around here. When I went to buy my townhouse I knew there was no way I'd want to heat 3 levels with a heat pump, but when my realtor eliminated heat pump from my geographic and price range in the MLS search, my choices went down by over half! I was shocked.

But, I have a new gas furnace and what a difference over the 17 year old system I replaced...

[OffWithTheirHeads]

11. If your really interested, here is the five minute version

Physics 1A. Water (at sea level) boils at 212 degrees F. At this temp, water can not absorb any more heat without changing state. It changes from a liquid to a gas, ie. steam. The only way to make water hotter than 212 F. is to put it under pressure like in a pressure cooker. The refrigerant in your heat pump or air conditioner acts much the same way. It boils at something like -68F.

The outdoor side of your heat pump contains this refrigerant. When air conditioning is called for, it puts the refrigerant under pressure until it turns into a liquid state. It is then sent to the indoor portion of the system (called a coil but basically just a glorified radiator) where the pressure suddenly drops. As the pressure drops, the refrigerant changes from a liquid to a gas and starts to absorb heat. The hot air from inside is blown across the coil and the heat is removed from it. The refrigerant, now in gas form, is then sent to the outdoor unit where it goes through a big coil (radiator) and a big fan removes the heat and sends it into the out door atmosphere. The refrigerant then goes to a compressor which puts it under pressure and turns it back into a liquid and the process starts all over again.

When you ask a heat pump to produce heat instead of cold, the process is basically reversed. It takes heat from the outside and releases it inside. Unfortunately, when it gets below about 40F. outside, there just isn't much heat to take so they don't work well. In most cases, the fix for this is supplemental electric resistance heat, (ie. electric strip heat) built into the system that kicks on when the heat pump can't keep up with the demand. The bad news is that this is really expensive to use cause it is nothing more than an electric heater and your meter is spinning like a top when it is running.

The bottom line is that heat pumps suck. They seemed like a good idea when we were all supposed to have free electricity but since that hasn't happened and isn't likely to, if you can switch to gas or oil or propane, do it.

In case you haven't figured it out yet, this is what I do for a living.
Good luck

[SCRUBDASHRUB]

13. Thanks for the info. Very informative.

I'd love to convert to natural gas, but I don't think the City will run a gas line (not sure what the deal is; maybe a certain # of residents need to agree of some crap). We do have a fire place that runs on propane gas, so that helps. I guess it's flannel sheets and cuddlin' when it's cold like this. Brrrrrrrrrrr...

[OffWithTheirHeads]

16. If you already have propane, you can convert!

The initial investment ain't cheap but if you are going to be there for more than a few years it will pencil out. If you need more info,
PM me and I will share what I know.

[DrGonzoLives]

15. Too much of a load

They just can't keep up - it's actually less energy intensive to cool than heat - there's generally less of a temperature difference between the outside and the set.

Of course, your heat pump may have broken down as well - it should be blowing at least warm air in.

[deadparrot]

17. My cat curls up on the registers and soaks up all the heat. nt

[jmowreader]

18. How old's the heat pump?

If it's one of the first ones, it may be a single-stage heat pump--which only has the heat pump system. Your resistive elements could be broken, if you have a multistage heat pump. Or your thermostat could be shot.

The newer multistage heat pumps have electric elements. They also require a multipart thermostat. This thing has to run the heat pump, run the resistive elements, determine when the heat pump alone isn't sufficient, balance the heat pump with the resistive elements...there is a reason why multistage heat pump thermostats cost $100.