Quote Originally Posted by AZag View Post
We are planning to replace our HVAC system and I have been talking to contractors and reading this (newly discovered, excellent) forum. After getting quotes from three reputable local firms, I find myself faced with a dilemma which I hope the pros on HVAC-Talk can help me resolve.

Here goes.

My house is in the Washington DC metro area. It is 36 years old, has two stories above ground plus a walk-out basement, and is approximately 3500 sq ft (excluding the basement which has no supply or return vents). We recently had all the windows replaced with double pane (which made a noticeable difference even with our very old inefficient system).

The furnace, evaporator coil and blower are in the basement. The a/c compressor is outside. We will retain this configuration with the new system

We’ve narrowed it down to two possibilities. They are as follows:

1) Carrier Infinity 58CVA 110-1-20, 24ANB7-48

2) Carrier Infinity 58CVA 110-1-20, 25HNB6-48

The thermostat would be the Infinity Control in both instances.

As you can see, the second combination is a “Dual Fuel” or hybrid setup; this is where it gets dodgy.

The first two contractors said that while a standard split system (#1) would certainly suffice, the hybrid (#2) would be much more efficient and would wind up saving us money over the life of the system. The difference in price between the two systems was not all that much (I know, no prices); both contractors said that it could pay for itself in just a few years.

Now I’ve read plenty of praise right here on HVAC-Talk for both the Infinity line and for Dual Fuel. I was ready to make my decision, then came the third quote.

This guy comes in and says: Hybrid? No way. He wouldn’t install it if we asked him. Why? To begin with, the heat pump runs in both cooling and heating seasons so it won’t last as long as a conventional A/C compressor and therefore doesn’t pay for itself in saved energy costs because we’ll wind up replacing it much sooner. He said ten years max, as opposed to at least fifteen for the straight A/C.
Further: we won’t be comfortable in the winter with the heat pump because it doesn’t heat the air as hot as a gas furnace. In a house as big as ours the air blowing from the registers (especially those farthest from the blower) will feel cool to the touch. This will supposedly cause us to raise the temperature at which the gas furnace kicks in, thereby reducing efficiency and defeating the purpose of the hybrid.
He said he had installed such systems in the past and had too many complaints, even had to replace some units because customers were uncomfortable. He also said that the heat pumps were more troublesome than the straight A/C compressors, and that in general, hybrid systems were harder for homeowners to operate and were also more troublesome because of their greater complexity.

But wait, there’s more. The third contractor also nixed system #1. The 58CVA was OK, but that two stage air conditioner? Fuggeddaboudit.

But, but, but, I thought a two stage compressor was more efficient, it saves energy and money and helps save the planet and dehumidifies and cools your house to boot, no?

No. The two stage unit with variable speed blower is no good for my house. With the blower way down in the basement, the A/C won’t have enough oomph to push the cool air up to the top floor when running on the first stage / low fan speed. We won’t be comfortable, so deep six the 24ANB7-48 and go with a 24ACC6-48.

So there’s my dilemma.

This guy scared the *&@% out of me. And what’s worse, he works for the company that has been servicing our old system for the past three years.

Yikes! Does he know something no one else does? His analysis goes against everything I’ve heard and read (including here on HVAC-Talk). But maybe I’ve heard wrong. Maybe I haven’t read enough.

What to do? Where to turn?

Asking a whole cadre of experts all at once seemed like a good place to start, so here I am on HVAC-Talk.

Any and all advice would be greatly appreciated, and I thank in advance all who take the time to respond.
I haven't heard of heat pumps going out sooner than AC systems. I would definitely go with the variable speed fan and two stage compressor. If the compressor is only single stage then you are usually the full power of the compressor on all days while the compressor is designed for the hottest day. Two stage just makes sense, less power usage when the demand is lower. Variable speed fans that are properly sized using Manual D to overcome static pressure loss will work just as fine as those constant speed fans in air delivery. You get the added perk of allowing the fan run at lesser speeds and therefore use lessor energy.

Hybrid systems also allow you to adjust between gas and heat pump, so you get the biggest bang for your buck. If natural gas is cheap (as in right now), use more natural gas... in the future if electricity is cheaper... use electricity. The system is adjustable.

Like any system I would make sure you are getting that load calculation and duct pressure loss analysis. Also, if you want to control humidity, you also need a thermostat that can handle that too.