Heat pump air temperature

amyspaetzle262October 28, 2005

I live in an all-electric home with a new Trane heat pump. I know the air a heat pump kicks out is considerably colder than what a gas furnace produces. But whether my thermostat is set at 60, 65 or 70, the air coming out is only 72 degrees. Even when the strip heat kicks in. Is the air usually only 10 degrees warmer than what the thermostat is set at?

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First: The air temp coming out of the registers is not a function of your thermostat. All the thermostat does is turn the unit on when heat is required, and turns it off when the setpoint temp is satisfied.

Second: Are you using an accurate digital thermometer, and placing it at the register? Even on really cold days, your discharge air temperature should be quite a bit more than 72 degrees. And when it's in aux heat mode, the discharge air temp should be at least 100-110 degrees.

If you really are discharging 72 degree air, then no - that's not normal. You need to have an hvac tech look at your unit. But first, make sure you have an accurate, working digital thermometer that you are using to check your discharge air.

    Bookmark   October 28, 2005 at 12:53PM
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Absolutely agree with Brad. Something is wrong here. What model do you have? Did your dealer perform a load calculation for sizing system? Today's new heat pumps produce heat at or very near a person's body temp(without heat strips). You should easily be receiving an air temp in the low to mid 90s. Your ductwork and its insulation properties should be checked. I would call my installer and have him also check unit particularly its charge, both liquid and suction.

Let us know what you find.

Good LucK!

    Bookmark   October 28, 2005 at 1:40PM
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One solution to your problem would be a variable blower motor controller such as the Fanhandler (see link below). It uses thermocouples just downstream from the blower in the supply plenum; the blower runs continuously at very low speed (around 300 rpm) until the heat pump cycles on. Then it ramps up the blower speed in response to temp rise in the supply air so it never blows cool air. I have had mine for a bit over 4 years with absolutely no problems.

Here is a link that might be useful: link to FanHandler site

    Bookmark   October 28, 2005 at 8:13PM
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OOPS!!! Disregard last post....I replied to the wrong thread..DUH!!

    Bookmark   October 28, 2005 at 8:19PM
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Hehehe Swing and a Miss!

I have a Trane XL12, and even on days when it's close to 32 deg. F I get air out of the vents that in the 100 to 105 range. Those are, of course, the vents closest to the unit. Farther away the air is a bit cooler.

    Bookmark   October 28, 2005 at 8:29PM
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A little update here...I have a Trane 2.5 T XL14i with a 3T variable speed air handler. I also forgot to mention I'm on a slab. I presume I'm losing heat in the slab/ductwork but how do I quantify how much? I called the installer (certified Trane installer) to make a service appt. and explained the air coming out is only 72 degrees. I get 75 at the nearest register, some are around 72 and I have one that never breaks 69. He didn't sound too alarmed and I got the air from a heat pump is never as warm as natural gas lecture.

    Bookmark   October 31, 2005 at 9:07AM
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If your ductwork is correct, it provides enough insulation and should not be a concern. Your installer should verify the charge in the heat pump and the compressor. In normal case the high-temp side should be at least in the high 90's.

    Bookmark   October 31, 2005 at 11:40AM
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Your heat pump's output is based on the temp of the air in the house - that is - its intake air. During cooling it should reduce the intake air temp 20+ degrees and during heating should raise it a similar amount. So, if your house temp was 50 degrees (burrrr) then the heat pump might only produce air that is 72 degrees. If your house was at 60, then output air is low/mid 80's and so on. If the heat strips kick on that should add some more - I'm guessing a bit but say 10-20 degrees more.

    Bookmark   October 31, 2005 at 10:53PM
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If your installer tries to feed you that line again, tell him to shove it in his pipe and come out and find out why your newly installed system isn't working the way it's supposed to.

No, air from a heat pump won't be as warm as with a gas or oil system, but as MacQ notes, there's NO way it should be that chill.

Don't take that brushoff for an answer. DEMAND satisfaction.

    Bookmark   November 1, 2005 at 12:30AM
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I have the same unit, 1.5yrs old. It puts out 85-95F, more when the strips are on.

Something is wrong with your unit. Or you're measuring the air at the inlet, not the outlet.

    Bookmark   November 1, 2005 at 7:24PM
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A little post service call update.
I was told the heat pump was a little over charged. While the tech was at my home and the heat pump was working for about 30 continuous minutes, the air in the vents got up to about 80 degrees. He said that was the best it would do until the aux. heat kicks in. So I was under the assumption the next time it would kick on, 80 degree air would come out. I was wrong. Outside temp was 38 this morning. Inside thermostat was set at 65...real inside temp was 63. The heat pump ran for about 10-15 minutes. The first few minutes I get the typical blast of 66 degrees and then maybe, maybe, it gets up to 73 or so. Never approaching the balmy 80 degree mark. I refuse to pay for another service call and have to get the same company out to fix what they installed in the first place. Any suggestions what could be wrong?

    Bookmark   November 10, 2005 at 9:03AM
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I stand by my post from Oct 28. I would write Trane a letter, with a copy to your dealer and even possibly the Trane wholeseller documenting the facts since the installation.Give them model and ser numbers. The Trane wholeseller usually has a residential specialist on their staff who might offer suggestions. You should be getting a supply air temp in the 90s,period without heat strip operating. You may have to get the address from your Trane Dealer.

Good LucK!

    Bookmark   November 10, 2005 at 10:21AM
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There is absolutely something wrong with this unit.

    Bookmark   November 11, 2005 at 12:11AM
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If your heating system is properly sized and properly ducted regardless of what type of heating system you have the output air should never be more than 10 to 15degF warmer than the room air.

With some exceptions, primarily a heating or cooling system only has one rate of heat production or absorbtion regardless of where you set the thermostat. The purpose is to insure an adequate circulation of the air during the heating or cooling cycle.

Heating and cooling duct systems are typically designed to provide two to three compete air exchanges per hourtherefore when designing the duct system you must begin by computing the total volume of the room in question.

Let us assume a room 10' x 10' with an 8' ceiling. The total volume of the room is:

10 x 10 x 8 = 800cu.ft.

If we desire 3 air exhanges per hour we must then move all the air in the room 3 times per hour or 800 x 3 = 2400cuft of air/hr.

Dividing 2400cuft/hr by 60 minutes per hr = 40cu.ft per minute. This will provide 3 air exchanges per hour, or we could say it takes 20minutes to move all the air.

Now less us consider the same room at 50degF and you set the thermostat to call for 70degF. During the first 20 minute period the air enters the heating unit at 50degF and is heated 10degF, thus the temperature at the duct will be 50+10=60degF. duing the second 20 minute period the 60 degF air again enters the HVAC unit and is heated an additional 10degF. 60 + 10= 70degF.

Once all the air in the room has been heated to the 70degF desired temperature the thermostat will turn the system off until the air cools and it is necessary to begin heating again.

If a heating system is improperly sized so that it blasts out hot air at greater than the 10 to 15 degf differntial you end up with severe stratification and drafts in the house.

    Bookmark   November 11, 2005 at 10:36AM
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My 12 year old heat pump, single digit SEER, with dirty coils, a slow leak, and probably in need of a filter change puts out air warmer than 72°.

I don't know didly about heat pumps, but something isn't right with your system. Hope you get it worked out.

    Bookmark   November 11, 2005 at 11:24AM
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Respectfully disagree with LazyPup example for typical residential installations. Using that theory it would take an extraordinary period of time to reach 70 degrees, which would be unexceptable to any home owner that I know.

As mentioned before a typical properly sized and operating heat pump will result in output temperatures in the 90's assuming that the house hasn't been allowed to cool to less than 60 degrees or so. The above assumes no auxiliary heat strips or other supplimental heating(dual fuel) being activitated which would raise the temperature output.

Your heat pump is not operating properly. Any one telling you different is lying to you. Even if the airhandler and heat pump were way undersized you would probably still get 90+ degrees at the vent...but with inadequate air flow volume (cfm's) of that 90+ degree air to properly heat your house.

As suggested before call the manufacturer and request that they get involved.

    Bookmark   November 11, 2005 at 1:23PM
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Heat pump temperature output is based on several factors, the outside temp is one of the most important. Outside temps in the mid 40's to 50's should result in a supply temp of mid 90's to mid 100's. Something is wrong with your unit. Found the following on a pro HVAC forum-----

Review specs ( BTU Capacity) to determine temperature rise at lower outside temperature.

BTUh = CFM x 1.08 * Temp Diff

Temp Diff = BTUh / ( CFM * 1.08)

3-ton at > 50'F outside might be
delta T = 30,000 BTU h / ( 1,200 CFM * 1.08) = 23'F

Inside Room Temp 72'F
_Air Supply Temp 95'F

___ Signficantly less when outside temp

    Bookmark   November 11, 2005 at 8:35PM
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O M G!!! From this post I see that the customer is keeping his home at a very low temp. he stated the house is set at 65 and room temp is at 63, when the system comes on. he (I have no idea which gender the poster is, I use he for my ease of typing) also mentions that it is 38degrees outside. with theese conditions I would think the system is putting out about 30 to 50% of it's rated capacity. under theese conditions a 63degree room will have air output temps of about 72 to 75 degrees. if he turns the thermostat another 2 degrees higher the auxilliary heat will kick in, and raise the temp another few degrees.
unless the temp in the home is kept at a higher temp, this is what the system is going to produce.
all you homeowners reporting higher temps, are not taking into consideration outside temps or inside temp setpoints.
it sounds normal to me.

    Bookmark   November 11, 2005 at 9:04PM
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vstech, Thanks much for bringing clarity to this thread. Your heat pump description was very helpful.

I have a question though about the heat strips. I was wondering why you would only expect her to get a few degrees of extra temp rise with them. Her location per "My Page" is Ohio. I would think she would need fairly powerful heat strips to augment her heat pump in that zone. It seems that even here in FL I get more than a couple extra degrees but I could be remembering wrong and I won't need heat for awhile yet so can't test it.

I don't really know that much about HVAC design. It just seems to me it gets cold in Ohio and she would need something other than a heat pump with little heat strips to keep her warm.

Would appreciate any light you can shed on this aspect. Thanks.

    Bookmark   November 14, 2005 at 3:29PM
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exactly, right,
in florida, the a/c load is much larger than the heat load, and the subsequent temp rise would be higher there. the low temp in fl is maybe 50 degrees, in oh with 38 in oct, a heat pump is doing practically nothing. it will be all strips, if the strip pack is not large, you will not get high rises. the customer mentioned it is a high eff system, so even if it is a large strip pack, they will be computer controlled, to keep the temp rise low to save $$$
if the heat strips are large, then the temp rise will be higher, when the strips kick in. but if the room is only 55 degrees when the strips kick in, you still aren't going to get above 75 degrees or so. the longer the unit runs and the colder the input air is, the computer will add in more and more resistance strips to the mix until the rise is sufficient to bring the room temp up to the setpoint. it does depend on the distance from register to the strips, where the ducts travel and the temp of the area where the ducts are. although if the unit is on a slab, I highly doubt the ducts are in the slab. also it depends on the volume of air in the unit. and air distribution. if a 20KW package is installed in a 5 ton heat pump, with 55degree air input, you are going to have some good heat coming out, but nothing like the 90 or 110 degree temps mentioned above.

    Bookmark   November 16, 2005 at 4:05PM
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Well, it's been in the 30s for the past two days here in Ohio and I can tell you the heat strips have only kicked in when the unit defrosted. It runs for about 20 minutes at a clip. House temp: 65 Air at register: 73 The cold air returns are all in the attic/ceiling and the ducts are in the slab.

    Bookmark   November 17, 2005 at 10:10AM
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With all due respect to the naysayers on this thread, your heat pump is not functioning like it should. Period! Again, you should be getting supply air temp in the 90s. Has your ductwork been thoroughly inspected?
My opinion.

    Bookmark   November 17, 2005 at 10:40AM
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TigerDunes...I am, I am. Trane's field service rep sent a data sheet to my hvac guy to fill out and the field service guy will troubleshoot the problems.
Regarding the ductwork...when I insulated up in the attic all appears normal. There were no tears and everything seemed firmly affixed. There were no dark marks in the insulation so I assumed no major air leaks.
The ductwork in the slab....who knows? But the supply air temp is pretty much the same around the house. Thanks for your input and I'll post the findings.

    Bookmark   November 17, 2005 at 12:22PM
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one thing to check, have a thermometor inserted at the air handler input and output points. immediatly before and after the air handler. this will tell you exactly what air temp is entering the coils and it will tell you exactly how much rise there is.
good luck

    Bookmark   November 17, 2005 at 6:10PM
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I finally turned my heating system on this evening.

When I did so, the outside temperature was 41 deg. F.

The interior temperature was 65 deg. F.

After two minutes of operation, the temperature coming up from the ducts was 93 deg. F., and the emergency/backup heat coils were NOT on.

    Bookmark   November 17, 2005 at 9:22PM
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This morning outside temperature was 33 degrees at my 1800 s.f. home in S.C. Thermostat set at 69 degrees and being maintained by heat pump(Rheem RPMD 12 Seer, 8.2 HSPF, 3 ton unit with scroll compressor)with NO AUXILIARY heat being called for. Temperature at vent nearest airhandler was 93 degrees.

Heat pump is indeed running longer to maintain set point... 15 minutes on 5 minutes off which indicates to me that I'm not too far off from the balance point at which auxiliary heat would be needed. Tomorrow it's supposed to get to 27 degrees as the low so I expect the auxiliary heat to be activiated.

    Bookmark   November 18, 2005 at 9:26AM
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November 11, 2005
Temperature Rise between register very near heat pump plenum and return air duct 6 feet from furnace

Measured Quantities. Heat Pump operation.
Location of measuring thermometers: Thermometer in hot air register immediately next to the furnace about 2 feet from plenum. Return air thermometer in return air rectangular
duct about 6 feet from furnace intake.
Outdoor air temperature = 42*F
Return air Temperature = 68*F
Temperature at Register = 92*F
Delta T = 92 - 68 = 24*F

Calculated Quantities. Heat pump operation.
2 ton Carrier 38YXA heat pump output at 42*F outdoor temperature = 22,000 BTUh
Furnace cfm setting for heat pump operation = 865 cfm
Delta T = (BTUh)/cfm x 1.08 = (22,000)/865 x 1.08 = 23.54 *F close enough to
measured delta T of 24*F.

Conclusion: The heat pump is working within specifications.

    Bookmark   November 18, 2005 at 11:18AM
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It got chilly enough here in FL last night to try my heat pump for heating. It's in good working order. Was mostly curious about the additional bump from the heat strips. The output temp was measured at a supply grill not far from the air handler.

Outdoor air temp: 55
Indoor air temp: 71
Supply air temp with no heat strips: 93
Temp increase with no heat strips: 22 (as expected)

Supply temp with heat strips: 104
Temp increase with heat strips: 33

Sadly, I don't recall the size of heat strips but in this case they add 11 degrees to the output temp. I would have thought Amy should have seen something closer to this when her heat strips kicked in.

    Bookmark   November 22, 2005 at 11:55AM
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To everyone with properly working heat pumps...I'm jealous. The Trane field tech sent a data sheet for my hvac guy to fill out on 11/17. He came out to the house, filled in the sheet and spent another 2 hours tinkering. After opening and closing my exterior doors (it was 30 degrees that day) the aux. heat came on and stayed on for another 40 minutes. The air temp at the registers finally made it to 90 degrees. The tech says, see, there's your 20 degree rise. You got to be kidding was my response. He said he would fax over the data sheet to Trane right away. Well, it's been almost a week and the Trane field rep never got the sheet and now he's on vacation until Dec. 1. The only bright spot to this whole ordeal is at least the air from the registers has boosted a little bit to 75-78 degrees.
Thanks all for your opinions/advice and formulas.

    Bookmark   November 22, 2005 at 12:46PM
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Amy: a small non-sequiter: are you a Schweitzer frau by your moniker?

    Bookmark   December 5, 2005 at 2:00AM
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I just had my 13 year old carrier unit replaced. They only replaced the outside unit, not the indoor air handler. The old unit was a 10 seer, the new one is a carrier that is 13 seer. The tech said he had to put an in-line filter on the smaller return line to the outside unit because he said the new unit flows faster and might knock loose some "gunk" form inside the indoor unit. I have noticed that it doesn't seem to get as hot as the old unit did. I wonder if the filter got clogged and thats why I'm having the same issue.............

    Bookmark   December 5, 2005 at 3:10PM
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I have gas heat in most of the house and have a large bedroom addition (450 sq ft)addition. This is our bed room. We like to sleep cold so turn the unit off at night. We also turn the unit off during the day when at work. When I got up this AM temp was 56 degrees in the room. Low in 20's outside. I have set the temp differential to 6 degrees to prevent the aux heat from coming on. It took almost 2 hours for temp to get to 68. When the room is cold, is it more economical to let the unit to run constantly by keeping set point max at 6 degrees or go ahead and let aux kick in and get temp up faster? Also my out put temp is 80-84 degrees when room is at 68. I have also been told it is best to leave set poin at 68 24/7 but that seems wrong because, as I use it it is only on week end days and early evenings and week nights briefly.

    Bookmark   December 10, 2005 at 6:31PM
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Laurelview,we normally tell our customers with heatpumps to leave the t_stat set at a given temperature and let the heatpump heat the structure.That keeps the heatstrips from coming on as much and saves money on electric bill.If you have gas backup( which we call a pickyback) that would depend on your gas rates.Our gas rates are very high here now, so electric heatpumps are cheaper.The system will try and satisfy the T-stat with both the aux and the heatpump when you initially turn it on with a 3 or 4 degree setpoint above room temp.Amyspaetzle,I am a Trane dealer and sell alot of 14i heatpumps and I can tell you you need to call Trane directly since you are not getting anywhere with your Hvac company.You most likely have a system that is improperly charged.They probably are not very well trained on the new 410a refrigerant.

    Bookmark   December 11, 2005 at 11:04PM
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Had a cool snap down here for a few days last week. Lows of 30°F one night and 33°F the next. The first night, I stopped in between jobs at around 7:30 PM, interior temp was about 63°F. Heat recovery to 70°F triggers at 12 AM. I don't know how much lower it got by then. I got home at 1:45 AM, the unit was still running, inside temp up to ~68°F. I was working in my detached garage for an hour or so, could hear the compressor running the entire time. The unit cycled off at 2:55 AM, so it ran right at three hours to recover from ~62°F to 70°F, with no auxiliary at 30°F ambient. Perfectly fine by me.

    Bookmark   December 13, 2005 at 7:32PM
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Last year, Nov/Dec 05, my son with a Trane heat pump began to have problems - failing to heat. The unit was 5.5 years old, just outside of warranty. In any case, it turned out to be the expansion valve on the condenser (outside unit). Once it was replaced, the unit worked fine. It did not take the tech very long to figure out the problem.

    Bookmark   October 24, 2006 at 2:16AM
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i have a 25000 btu package heat pump 2.5 tons, i have foam filled walls R38 in the walls and R52 in the attic, i can only get 11 degrees difference in my cooling temps, its 70 in my house using a digital thermometer and i can only get 59 degree air and its 98 outside my unit is a 14 sheer rheem bought 8 months ago, never has worked right to me but thats why im asking is 11 degree difference normal in a package unit, it does about the same in heat, and what may be the problem if its not normal. thanks gang

    Bookmark   August 11, 2007 at 5:29PM
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Things to keep in mind. Room temp, Thermostat setting, outside temp, how well house is insulated. With that being said, my heatpump blows about 95* air out of the register at 40* outside temp. Room temp is 72*. Below 30* it runs continually without aux heat kicking in. It is 25* outside right now and the air temp out of register is 82* with a room temp of 71*. Room temp is going down because the H.P is not able to keep up with the outside temp. Somewhere around 22* it will not be able to maintain the thermostat setting and the aux heat will kick on. I think I am doing pretty well. Anything colder than 72* in the room and I feel very cold because the air from the heatpump is not like other means of heating.

    Bookmark   December 5, 2008 at 12:00PM
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Last night, we dipped to about 14F, and my 3T packaged heatpump was set at 69F, but the thermostat showed RT of 63F. Aux heat was indicated to be on. After 1 hr, still no change in RT. This is typical as the aux system seems to come on regularly with no appreciable increase in register temp. Airflow through the ducts appears good, which IMO implies good sealing. Also, ducting is insulated.

To me it seems this unit is not working properly, mainly the aux system. Can anyone provide a description of what should be happening so that I can discuss it with the tech?


    Bookmark   December 22, 2008 at 8:38AM
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I, too, am having the same problem with a 16 seer 2 speed American Standard (same as a Trane)Heat pump. I have been arguing with the independent dealer for about a month and a half. I keep my house on 68 winter and summer. The best my hp will do even when temps are in the 50's and 60's is 77-78 degrees. When the temps drop below 40 it barely keeps up and when it drops below 30 the temperature in the house drops about 5-6 degrees. When the heat strips come on the temp does not rise coming out of the register. My father has a 10 year old 12 seer Trane that is putting out 95 degree air. My sister has a 15-20 year old unit that is putting out 100 degree air. We all live in the same county in upstate SC. They were getting those temps from their's when the outside temp was below 25F. I sure wish someone could get us an answer.

    Bookmark   December 23, 2010 at 1:38PM
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    Bookmark   January 16, 2011 at 11:41AM
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I am in the Washington DC Area looking at new HVAC system. People are telling me that the newest heat pumps will work and warm the place when the temperature gets down in the 20's. I thought they really couldn't do the heating job and need a backup system when the outside temperature got below 32 degrees. How low can they work now

    Bookmark   June 1, 2011 at 5:41AM
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My 2.5 ton three day old Rheem heat pump is not cooling. I live in Texas. I set the therostat at 75. The temperature inside continued to rise, reaching 80 degrees. It was 99 degrees outside. The temperature fell only after 7:00 p.m. I called technicians. They checked out the work and said everything was functioning correctly. They could find no reason as to why the unit will not cool. What can I do?

    Bookmark   June 3, 2011 at 8:29PM
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I had this same issue pretty much. Frigidaire 13 seet 4 ton unit.

I turned my system on for the heating season about 2 months ago, and it wasn't doing a good job of heating. I had the thermostat set at 63, and the house would go above 61, ever with it 48 degress outside. I had a different service company come out today, and the air temp out of my vents in my family room was only 65! He checked outside and he said I was slightly low on the r410a, and he filled it back, and I then had 95 degree heat out of my vents. I'm just worried why he had to fill it. Again, he said it wasn't that low, but that's what the problem was. I hope there isn't a small leak as it shouldn't drop at all in 3 years, right? It worked great over the summer.

    Bookmark   January 6, 2012 at 5:43PM
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