dual fuel heat pump vs standard gas furnace and ac systems

15 years ago

I have been considering various types of systems, primarily dual fuel heat pump with gas backup furnaces, and have two general questions. After very helpful comments from comentators here on specific systems quotes, I decided to investigate further the merits of dual fuel systems versus other setups. I know that I do want a gas furnace in the package, whether as a backup with a hp or in combination with an air conditioning unit.

1. I have received information from several sources that studies suggest heat pumps last for about 12 yrs. versus 15 years for equipment in standard setups (I assume this would be for furnace a/c combinations). Is this information relatively accurate? I believe a study was cited but do not have the citation.

2. I am "cold natured" so in addition to efficiency and eveness of temperature, I am especially concerned about the quality of heat and also the rapidity with which my house will "warm up". I also like to feel the warm air. My understanding is that the air temp. at the vent for a hp while heating is 80 to 90 degrees and may not feel warm (some "cold natured" people have commented that they never felt "warm" with heat pump heat). In contrast with a gas furnace the temp. coming from the vent is higher, and the air feels warmer. Is that correct?

3. Regarding gas furnaces that achieve efficiency by running at a lower speed (fan speed I assume), would the lower speed affect the feeling of warmth or the rapidity with which the air heats? Would this differ between variable speed units that vary speeds with temperature and two stage or single stage units that are pre set to run at lower speeds most or all of the time?

4. I also understand that the dual fuel heat pumps are generally more expensive at purchase than comparable (brand, rated efficiency etc.) gas furnace/standard ac combinations. I also understand that the potential advantage of the dual fuel heat pumps would be in running cost savings when the heat pumps are providing heat above 40 % and the magnitude of those savings (if any) depend on the cost of natural gas relative to electricity.

Is my understanding generally correct?

Sorry if I am belaboring all of this. The experts on the forum have been so very helpful, and thank you for your patience.

Regards, Beth

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Comments (2)

tigerdunes
15 years ago
beth

answers going down your list....

1.length of life can vary depending on use, environment, yearly PMs, and quality of original install

I personally believe 15 yrs min is a good target for good equipment and believe me there are some real junk HVAC on the market

2.you can not compare today's HPs against those 10 yrs and older. as different as night and day especially in the area of supply temp. Supply temp on a properly charged HP should easily be in low 90s depending on outside temperature.

one reason I put in a dual fuel system was because while I liked the idea of operating savings of electric vs nat gas, I was somewhat skeptical of the acceptibility by myself and family as far as comfort. No problem. it is fine. In fact, I wish I had gone with an air handler rather than backup var speed furnace. This past season I used about 60 therms of nat gas for heating as the heat pump did the primary heating.

3.I really think you are confused on question 3. Temperature is temperature regardless of the speed it is delivered. On today's high eff furnaces that are two stg (newest mdls can have three stgs) models with var speed blowers, the heat that is delivered is what I call soft, quiet, gentile heat as opposed to the conventional furnaces that deliver very hot noisy heat. The temperature from the high eff var speed condensing furnaces while higher than today's high eff heat pumps is lower than the hot blast of non condensing furnaces. You may get some debate on this subject but based on my measurements that statement is correct.

4.There is no such thing as a dual fuel heat pump. A heat pump with backup furnace(as opposed to an air handler with heat strip backup) is called a dual fuel or hybrid application. The operating savings depends on the price of electricity and price of nat gas as well as the efficiency of equipment for a high eff heat pump and nat gas furnace. A heat pump provides AC just the same as an AC condenser.

I believe I have given you the fuel comparison calculator in your previous thread which offers an accurate indication of possible savings.

I really believe you are overthinking your situation.

These are the minimum specs I would use for HP selection.
15 SEER, 12 EER, 9 HSPF
full BTUs in both heating and cooling mode
matching var speed air handler or var speed furnace
scroll compressor preferred
electronic demand defrost
thermostat that controls blower speed like the HW VisionPro IAQ

IMO
agfworth
11 years ago
I bought a dual fuel heat pump system in 2006, and I've been pleased with overall performance. I'm in the Athens, GA area, so my gas usage for winter heat has been extremely low. I was more interested in efficient air conditioning; summer is when my bills are highest.

I did a lot of research about the options but NOT about the brands. I've had trouble with my Bryant system. Seems that the condenser in the model I bought was very poor. When I had more problems recently, I asked many very knowledgeable property owners (one owns multiple rental properties) for recommendations; the brand recommendation was consistent: Trane.

Here's what happened with the Bryant equipment.

The condenser failed after two years. The equipment was still under warranty, so I got a new condenser at no charge. Installing the replacement, however, cost over $700.

This summer (six years since the system was installed, four years since the condenser was replaced) the condenser failed again. This time, my dealer was able to use a Bryant program, to replace the entire external unit with an upgraded unit. I had to pay about $1200 for the new equipment (full cost about $6,000), and it comes with a new 10-year warranty. The installation was simpler and cost $300.

I am more confident playing $1500+ for a different unit, with a condenser from a different manufacturer, than paying $$700+ to replace the condenser with another condenser from the same manufacturer (not Bryant, a supplier to Bryant).

I would prefer getting a Trane unit, but that would be much more expensive. This new unit from Bryant may be reliable, but I am uneasy after my experience with their equipment.

The installation cost of replacing the condenser after two years wiped out any savings that the system provided.
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dual fuel heat pump vs standard gas furnace and ac systems

Comments (2)

tigerdunes

agfworth

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