2 stage AC or heat pump?

[troyport]

This spring, had a new modulation propane furnace installed, using my central AC system that has been in place since 1999. So far, I just love the new furnace! And the installer addressed some air flow restriction issues on my return line so the AC worked better this summer. But, the AC system had a few minor breakdowns over the summer, due to age. I am thinking about replacing the AC system early this spring, to avoid a total failure right when I need it most.
The cost difference between a 2-stage AC and a 2-stage heat pump is not that much, and I am seriously considering going with the heat pump to have a hybrid heating system, which I think will pay off considering the cost of propane! Question is this: My old AC was just a nice bare-bones workhorse.. simple contactor that fired up the compressor and condenser fan.. Not a lot of stuff to break. A heat pump would be more complicated.. therefore more stuff to fail. So my question is long term should I go for the heat pump or just an AC system? Thanks, Mike

[ga-hvac-tech]

First: We really need to know where you live; city/state or close to a larger city/state is fine. Climate conditions are important to your question. Example: In northern climates where AC is only a mos or so... 2 stage AC (16 or 18 or 20 SEER) is not worth it. However in an 'oven climate' like Phoenix it is definitely worth it. Contrary to some sales folks opinion , higher than 16 SEER AC in my area (Atlanta), it is hard to re-coup one's investment. If you are approaching this for the heat value more than the cooling value; then using 2 stage equipment and over sizing one step (AC adequate in low stage) will give you more heat capacity to a lower outdoor temp. For folks reading this thread; he already has a VS drive furnace (the modulating furnace); one should ALWAYS have a VS drive furnace or air handler when approaching higher efficiency equipment.

Since you are restricted to LP gas for heating, setting up a dual-fuel system is a good idea... LP is expensive and LP furnaces tend to need more maintenance... LP is a dirty fuel and causes issues with equipment. The less time running that LP furnace, the better on both issues.

Might want to remember a HP runs year round; so normal wear on components will shorten its life compared to straight AC. Two stage equipment is not that complicated, however it does require more maintenance (cleaning and filter changes). I would recommend a media style air filter if you do not already have one. Also, you will need some form of DF (dual-fuel) controller; lots of high end thermostats can handle this issue.

Post your location... we can help more knowing the climate.

[BaldLoonie]

With propane heat, I'd certainly be thinking of a heat pump. Personally I'd stay a good single stage.

[motoguy128]

With propane heat, I'd certainly be thinking of a heat pump. Personally I'd stay a good single stage.

+1. IF you have propane, dual fuel all the way for sure. The effciency of heat pumps is actually slightly lower in 1st stage, so you don't gain much with 2 stage. 2 stage is more for comfort and effciency in cooling than heating.

[George2]

With propane heat, I'd certainly be thinking of a heat pump. Personally I'd stay a good single stage.

I agree with B.L., EXCEPT, I would go with the 2-stage H/P. No offense, B.L.!

[wahoo]

+2, I've got a single stage 14 SEER HP on our office 95% LP furnace. Works fine. With the variable speed gas you can probably get 15 SEER in single stage HP. Lots less complex controls in a single speed HP. Check with your electrical supplier for special pricing on electricity if have a HP. Ours discounts it @40% during winter with HP.

[troyport]

Thanks for the replies... I live in rural NE Ohio.. The AC is in use probably 3 months out of the year, but it is needed, we get some brutal humidity! I wasn't sure if I was allowed to mention brand names, but I have a 96% 80K modulating furnace, I had the big filter installed with it (something like 6" thick?) and the t-stat is the best one I could get, full-communicating so once I have this AC/HP in place I can tell it when to lock out the propane, etc.. I really like the system. BTW, on a really hot sunny humid day (like 98 deg) with the kids going in and out of the house the 3-ton AC will run almost continuously, so I think that is just about the correct size. Thanks!

[ga-hvac-tech]

THX for the location... helps.

Two stage comes in even ton sizes... so a 3 ton will be around 2 ton low... and a 4 ton will be around 2-3/4 ton low.

If you have a communicating T-stat from the same manufacturer of the furnace, you are most of the way towards a really nice system. Personally, I would go ahead with 16 SEER 2 stage HP, and would go with 4 tons. On the AC side low will cover most of your needs, with the high available for a really HOT day or load (think party with doors never closing). You would get the added HP capacity for the winter, with some reserve AC for the summer. And the VS drive furnace with its dehumidification cycle will cover mild over-capacity of AC. Note you probably will need a new lineset (copper tubes) from the inside to the outside. Have the HVAC guy look at the ductwork to be sure it will handle the 4 tons of airflow. Sometimes I mount a 5 ton coil with a 4 ton HP (did that a few weeks ago) in your situation... tends help the HP and the AC dehum cycle also (some would disagree with dehum, works on my installs).

Just curious, what brand of equipment?

Hope this helps.

[troyport]

goodman.. with the comfortnet.

[motoguy128]

How many of those have you installed? How have they performed? The heating performance of their heat pumps are very good without having to massively oversize indoor coils

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[Quantumstate]

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[ga-hvac-tech]

How many of those have you installed? How have they performed? The heating performance of their heat pumps are very good without having to massively oversize indoor coils

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Might want to look at the spec books printed by the manufacturers... Specific matches and specific ratings (AHRI stuff). You will find oversized coils perform better in many matches, especially in high SEER/EER equipment matches.

And on the technical side, think with me for a minute: In AC mode, you have a larger coil outside and a smaller coil inside. When you go to HP mode, you are reversing the usage of those coils... thus forcing the indoor coil to release a LOT of heat. HP's are a lot more sensitive to charge in heat mode than AC mode... for this very reason... they cannot give off the heat inside... thus they go out on high head pressure. Older HP's used an accumulator to store some of the refrigerant in heating cycle, now they use a charge compensator. Now how to resolve this... simple... larger coil inside.

To answer your question... generally unless it is a slum lord install... I ALWAYS use a slightly larger coil inside. Most are 3 ton coil for a 2.5 ton HP... works just fine. Better to have a TXV at both ends BTW.

[ga-hvac-tech]

How about with Trane? For a dual-fuel system with 3 ton HP would it be useful to go with a 4 ton coil?

Need access to the AHRI matches. If your contractor does not even know what those are.... well what are the chances of a quality install? Remember: Installation is more important than brand of equipment.