you will never get fast temperature increases with a heatpump. Even if outside temperature is 45-50.

Are you saying you have a 3.5ton and 3400 sq. feet and your oversized? I definitely don't think your oversized if you have 3.5 tons for that sq. footage.

I get about a 26 degree temperature rise coming from my vents when its 50 degree's outside. I have a single stage 3-ton heatpump with 3.5 ton coil with txv. This temperature is a achieved after its been running a while. It takes some time to get this temperature rise. It doesn't happen after only running a few minutes.

If you have dual fuel, don't be afraid to let the natural gas be used to bring up temperatures fast. Thats what gas is good for. If you have a good t-stat you should be able to control all of this. What your t-stat controller?

I personally wouldn't bother with the 1st stage of your heatpump when in heating mode unless its 50 degrees outside or above.

john

Here is the matching AHRI match with performance/eff numbers.

3261198 Discontinued Systems INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA648A31 CNPV*4821A** 58MV(B,C)100-20 45500 11.00 15.00 47500 8.90 27800

A nice system, probably overkill with the 95% eff furnace for a relatively mild climate like Seattle. It is unlikely you are oversized at 4 tons for 3400 sq ft. I assume you have the Infinity controller. Correct?

First, the stop and go between the stages of this mdl heat pump is normal. It is a feature that I don't like but is the way this condenser was engineered.

So to your problem. Two issues stick out. I don't like setbacks like you have. Heat pumps are good at maintaining temperature but can be very slow to recover under certain circumstances. I do not recommend a setback more than three degrees. Extreme setbacks like you have can be false economy. I assume your furnace is locked out at a specific outside temperature. But the low supply temperature at 45+ degrees outside temperature is not normal. It should be in the low 90s at a minimum if not higher. This suggests that your refrigerant charge is not correct. You need a seasoned Carrier Infinity tech with charging charts to check this out. I am assuming ductwork has been looked at for obvious leaks/restrictions. Evap coil also should be inspected for any buildup. Return ductwork should also be inspected. Split levels are notorious for heating and cooling. You have adequate return?

I would get several supply temp readings at different locations in your home at different times of day(early, midday, afternoon, evening). Document this with time, location, and outside temp.

do this over several days, review, and post back. then you have the ammunition to call installing dealer and complain with facts.

IMO

Thank you for your responses. Your insights and guidance are exactly what I was hoping for. To answer some of your questions: the controller is an Infinity (rev B); I'm certain the duct work leaks, but since all of it is enclosed in interior space (no crawl space, exterior walls, or attic) the leaks stay within the home. I had the air return in the basement improved and added 3 more vents when the system was installed; it can really breath now. It has a 20x25x4 pleated filter that I change regularly. The unit is 4 tons, but manual J calcs indicate it should be 3.5 tons. So, it's slightly oversized. I don't think I explained the setback properly: at 5AM it goes from 63 to 65F, at 2PM it goes from 65 to 67F, and at 4PM it goes from 67 to 69F. I don't think I'm asking too much of the heat pump. Should I change this? I'm not an HVAC pro, so I've been referring (incorrectly?) to "balance point" what you refer to as "furnace lock-out".

@tigerdunes: I'll inspect the interior air coil, but since the system has always performed poorly, I suspect that a dirty coil would show up as degrading performance over time? When I contact the service tech I will be certain to insist that they verify the refrigerant charge. But most importantly, thank you for the guidance on the vent temperature experiments. With that data I'll know that they can't give me a "no problem found". I'll report back when this is resolved so that other home owners in similar situations will be better armed.

OK, I ran some tests and gathered temperature rise data. I placed a bead thermocouple on the cold side (air filter housing) and the hot side (in the duct, 4" after the coil) and recorded the temperature difference at various run times. The CFM data came from the Infinity "service" menu, so I don't know how accurate that is. I have 20+ data points in a spreadsheet, but here is a smaller representative sample.
Cold side temp/hot side temp/CFM/outdoor temperature (all high stage)
62.6/91.4/1118/45 :: 62.4/92.4/1204/52 :: 65.2/87.2/1400/40 :: 61.8/87.0/997/36
Low stage data
63.4/72.2/882/44 :: 60.2/66.8/627/36 :: 62.4/70.4/627/39
I ran across an HVAC handbook that gave a formula for heat output:
BTU/H=1.08*(TempHot - TempCold)*CFM. If that formula can be believed, I don't think my heat pump is doing too good :(
So, is this enough data to draw any conclusions?
Thanks,
John

The Infinity heat pumps are only available in whole ton increments. Therefore if you manual J calculation was 3.5 tons, then the 4 ton size is correct. The AC and HP should operate in the low stage during milder periods. You would have had to purchase a single stage condenser in order to get a 3.5 ton unit.

Has your furnace and condenser had maintainence service since it has been installed? Maybe you are low on refrigerant or perhaps you have some other set up problem. I don't own a heat pump so I can't offer specific advice.

What are you gas and electric rates? I am confident you electric rates are lower than mine, but the cost of natural gas continues to drop. You should evaluate your furnace lock out and HP lock out temperatures. The Carrier 58MVC furnace is very efficient. You should be operating the majority of the time during the cold winter months.

UPDATE: the problem has been resolved and I'm providing this update to aid other homeowners who may have similar performance problems. Special thanks to Tigerdunes who instructed me to record the temperature rise across the inside coil. That data made it much easier to convince the techs that there was a real problem. To recap, the HP put out about 70-75% of what it should in high stage and 30-35% in low stage. Initial thoughts were leaky suction valve in low stage part of compressor. It turned out that the piston on the outside unit (heat mode metering device) was never installed. I was surprised that it could put out any heat at all. The tech conferred with his peers and learned that debris in the piston chamber or a wrong size piston would give below spec performance as well. So, if your heat output seems low or your are power bills higher than you expected, then check the piston.

When you say "heat mode metering device" on the outdoor unit, are you referring to the TXV (thermostatic expansion valve)?

The condenser's TXV was not installed at the factory?

@garyg - No TXV. I did some checking on other Carrier/Bryant heat pumps and learned that none of those had heat mode TXVs. They all use the older piston technology as the metering device. In cooling mode, however, it seems that they all have TXVs.

ZG: I'm not sure I fully understand this, but that's ok. Are you saying that the system ran fine in cooling mode but was terrible in heating mode? And have you been running it since repaired and do you notice the difference?

Weedmiester - The behavior was that the heat pump was putting out the heat of a 2.5 ton, but is supposed to be a 4 ton. So, it was sort of working, making it hard to detect the problem, outside of high power bills. As far as the AC mode, it seems to be OK. I don't use the cooling mode much ( 52 hours for the last 2 summers total), so it's hard for me tell. Once the piston was installed, the heat output was much hotter, almost double the temperature rise. It works great now.
Some HPs use TXVs in heat mode. The Carrier (and Bryant) HNA & HPA series use a piston for heat mode. The piston looks sort of like a large acorn nut with a small hole down the center and acts like a venturi. When the refrigerant reverses, the piston slides back allowing the liquid refrigerant to pass around it (cooling mode). In heating mode, it slides forward, and the smooth dome seals against the narrowing throat of the refrigerant line, forcing the fluid through the small center hole, i.e. venturi.
The point I wanted to make is that if a home owner has a heat pump that performs poorly, they should consider inspecting the piston for the right size, if it's there, and even if there is debris preventing the smooth dome of the piston from making a proper seal. It's not always dirty coil or low refrigerant charge.