Heat pump/ furnace question

[techman]

That is normal. As it gets colder, the output capacity of the heat pump drops (some people think that the heat pump's efficiency drops in cold weather - it does drop somewhat, but the major issue is that the capacity, or amount of heat it can produce drops). Also the heat loss of the house gose up as it gets colder out.

If you graphed the heat loss of the house vs. temperature, and on the same graph plot the heat pump output vs. temperature, the 2 lines would cross at some temperature. This point is called the "balance point", which is where the heat pump can just maintain the house temperature. Below that outside temperature, additional heat is required to maintain the house's heat. High end heat pumps have a microprocessor controller that will have a settable balance point temperature. When it is above the balance point temperature outside, the aux heat is disabled (except in emergancy mode). This helps save money if you bump up the thermostat a few degrees, since the electric strip will not come on.

So if you are near or at the balance point, the heat pump may run continuously, without any auxiliary heat. A bit colder and the aux heat will start to cycle on a bit, and the heat pump will keep running. At this point the heat pump is still making cheap heat, but not enough of it.

A heat pump will make efficient heat to 0 or below, but at a decreasing capacity. Get below 0 and usually the amount of heat produced starts to equal the losses in the system, to not much net heat is generated. It will run without doing any harm, but not producing much heat. At that point the aux heat is providing most of the required heat.

paul

 

[Volfandt]

I don't want to repeat the correct info thats already been posted but I'll go on ahead and add some very experienced heatpump "user" observations /forums/images/graemlins/grin.gif

As has been said, emergency heat setting is really only used in an emergency type situation such as when the heatpump fails. When you run in EM your spinning your electric meter like crazy.
That said, there will be times when the thermostat will turn it on/off based on demand and a few other factors. It's best to let the thermostat control emergency heat in non-emergency situations.
From my observations, you don't want to vary your temp settings no more than 2 degrees. A heatpump works best in maintaining a temp as opposed to trying to catchup to it.
It is not abnormal for a heatpump to run continuously once the temps dip down in the 20's or lower. And even tho it's running quite a bit, it's still useing less electricity than strip heaters and/or your electric furnace.
Generally a heatpump only heats the air to alittle higher than your body temp of 98 degrees. That being the case, most folks think that it isn't producing heat when in fact it is. Step outside for a moment or two then come back in and place your hand over a register and you'll feel heat /forums/images/graemlins/grin.gif

There will be times when the thermostat will turn on the emergency heat to either catchup once the thermostat has been changed or maintain the inside temp when it gets very cold or when it goes into defrost mode. You can instantly tell as you'll feel the "heat" of those expensive heaters kicking in.

Defrost mode. When the temps drop down into the 30's the outside unit's coils will start to collect frost and ice up. This of course hinders it's ability to transfer heat so when the temps drop to a set point the unit will go into defrost mode. Basically it reverses the refrigerants flow away from the inside coils out to the outside coils and uses this hot refrigerant to defrost the outside coils. When this is occuring the outside fan will stop and all you'll hear is the ompressor running (or maoning away). After a few moments you'l start to see steam rising from the outside unit and a few moments later you'll see quite a bit of steam once the coolent flow is reversed back to heating mode and the outside fan kicks in. This is normal so don't be concerned. It may do this hourly or bi-hourly based upon outside temps.
Also when the unit is in defrost, your emergency heat/backup heat will come on to heat your house while the hot refrigerent is redirected outside to defrost the outside unit.

The best type of thermostat to have is an automatic setback.
I'll use mine as an example.
From 8am to 5pm M-F my thermostat is set to maintain 68 degrees. From 5pm to 11pm it's set to maintain 70. From 11pm to 5am it's set to 68 and from 5am to 8am it's at 70. It's also set to maintain 70 all day on Sat & Sun and drop to 68 at 11pm. You can definitely feel the difference between 68 and 70, my wife and daughter will tell you /forums/images/graemlins/grin.gif /forums/images/graemlins/grin.gif
It doesn't perform sudden changes either, it does a gradual change well before the time it's required to change the temp.
What all this does is to try and maintain a confortable inside temp at the lowest cost possible.

I've run heatpumps for 24 years now and I've been happy with their savings over other heating solutions.
My present setup is a dual fuel heatpump which uses natural gas as backup/emergency heat and I've programmed my heatpump not to even think about useing the furnace until the outside temps hit 25 degrees. So far it's kept the abode comfortable.
Good luck
Volfandt

 

[Code54]

OK - I was SOOOO off base it was not even funny. Thank you to everyone for the info. I got all concerned when I heard the heat pump running a bunch and flipped that switch to Emer - bad idea it appears - oh well at least the power company will be happy with me this month....
I was afraid I was "burning" the heat pump up with all the running - now I get it. How long do you expect to get out of a heat pump and is there anything I should do to maintain it?
Thanks again

 

[gator]

20 to 25 years at least, if maintained (depending on location of air handler).
Maintenance:
Keep outdoor unit clean, hose off at least twice a year, to include coils (wax, yes wax the entire unit with car wax, you'll be surprised how much longer you can make the outdoor unit last by doing this).
Use a high quality filter in your return duct(s). The typical fiberglass, 3 for $1.00 filters, as my college instructor use to say, will catch footballs, but anything smaller will end up on your coil, affecting effeciency. If you haven't had a complete check up (charge check, coils cleaned), schedule one for the early summer from a reputable company. One cleaning of indoor coils in addition to using a high efficiency filter is usually sufficient for a couple of years.
A ounce of prevention is worth a pound of cure (and money).

 

[Bird]

</font><font color="blue" class="small">( 20 to 25 years at least, if maintained (depending on location of air handler). )</font>

This has been a very informative thread for me. I learned a little from the guy I hired to check out this system before I bought the house, a little from other research on the web, and now from this thread. Glad to hear it has an expected long life (mine shows manufactured June 1999 and certainly "looks" almost new). But I wonder about that "depending on location of air handler". What makes the difference? Mine is the "split system", air handler in the attic, and not a dual fuel system. The house is total electric.

 

[Volfandt]

I forgot to address longevity. /forums/images/graemlins/grin.gif
Of the 3 heatpumps I've had,
The 1st was already in our 1st house. It was a Rheem package system that was about 5 yrs old, we lived there 7 yrs and it was working fine when we sold.
Problems, had to replace the outside fan.

The 2nd was a Sears spit system that we installed new. It lasted 17 yrs before it needed replacement. It may have lasted longer had we not have had to move the outside unit to accomodate expansion. Seems the problems started after that. (low bidder isn't always the best way to go....)
Problems, inside coil got stopped up due to debris in lines, replaced outside unit fan.

Present system is a Carrier dual fuel split system, it's 5 yrs old and going strong.

I use premium filters (approx $15 a wack, I have two filters) due to the Mrs's allergies.

Volfandts

 

[gator]

Bird,
The reason I said depending on location of air handler is because:
The air handler typically has 1/2" to 5/8" fiberglass bat glued the tin inside of coil and fan area. When the air handler is exposed to the outside warm moist air in summer, and cool moist air in winter, as in attics and under houses, the heat and cool cycles will cause condensate moisture to form on outside of air handler (the fiberglass bat insulation help , but doesn't prevent) the more humidity in air, the more condensate forms on air handler. After years of this, the paint chaulks and quits protecting, and metal and moisture = rust and corrosion. When I used to install them, we would have to wrap the old air handler we were removing from attic in visqueen, to contain it, as it crumpled pieces as we were removing it.
Now, if the air handler was in the house, such as a closet, this is a conditioned (heated/cooled) space, so the air surrounding the handler is not the same as the outside air, temp and moisture wise.
I hope this makes sense, that a air handler in a conditioned space (inside house, not attic) will normally outlast an air handler exposed to the outside air (attic, under house)

 

[geneP]

I have a Trane heat pump in my house. I had a switch installed in the outside unit to cut in the auxillary strips at a pre set outside temp. The strips run in conjunction with the heat pump. I'm in Mississippi so we don't have a lot of nights when the temps get below thirty, which is where I have my switch set.

 

[jwstewar]

You said that it didn't seem like it wasn't switching over to the "back-up" furnace. That could be true. When they first installed our first heat pump (6 years ago) they didn't install an outside thermostat. The heat pump would run and run and run and we would get colder and colder and colder inside as the temps went down. It never would kick the furnace in until it go 3 degrees below what we had it set at. The installed said, we kick it over to emergency heat. I said that I shouldn't have to be playing with the thermostat all of the time to change the settings every day based on the weather. Finally I raised enough of a stink they installed the outside thermostat. Things have been fine since (well except for the hail storm this year that destroyed the outside unit). I keep the outside thermostat set on 30. Anything above and the heat pump runs, below that and the propane furnace runs. We do not have any of the heat strips that heat strips that people are mentioning. When we were looking at replacing the outside unit this year, one of the companies wanted us to do away with the furnace and go to heat strips. I wasn't convinced that was the best way to go - needless to say they didn't get the job. /forums/images/graemlins/laugh.gif

 

[lrowe]

I could use some help understanding what is happening with our newly installed Trane dual fuel heat pump/gas furnace with variable speed fan. The unit has been installed for 4 days and has mostly run 'aux heat mode'. It appears to have difficulty raising the house temp three degrees (from 68 to 71). The unit runs most of the time. How can I tell if the Aux heat is using the gas furnace? /forums/images/graemlins/confused.gif Also, this morning was the first night the temp dropped below 30. When I woke up this morning, the house was cold (inside temp was 64 set to temp 79 and no fan was running). I set the thermostat control to emergency heat and was able to get the house warmed back up to 70 over the course of an hour. Does anyone know what could cause the system to drop to 64? /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif I have it set now to 'heat' and it appears to be working. I will call the installers on Monday however, I believe that they are not as well versed in getting these systems set up to work together and I have gotten conflicting info from the installer and the sales guy and don't know who to believe. The installer did have difficulty getting the gas furnace backup to work with the outdoor sensor and had to add a TA+ board. He told me i might need another board outside to control the system. The sales guy says i should just set the thermostat and the system will do the job. I'm frustrated because after spending a significant amount of money I feel like we should have just gotten a high efficiency gas furnace and called it a day. Did we make the wrong choice?