Heat Pump With Natural Gas Hot Air Heater

Hello to the group.

My daughter who lives in southern New Jersey uses an AC and a natual gas, hot air heater. Both the AC and heater are approching 20 years old and will probably need to be replaced shortly.

I suggested she replace the AC and the natual gas, hot air heater at the same time with a Carrier, infinity, hybrid heatpump and matching natual gas heater. I understand the Infinity controller will manage which unit will heat or cool the house dependent on outside temperature and other factors.

I believe the typical electric heat strips associated with heatpumps would be omitted from the hybrid heat pump system and the gas heater would replace the heat strips with the natural gas, hot air heater to back up the heatpump when the outside temperture drops below a predetermined temperature.

Based on my experience with an Infinty heatpump in North/Central Florida, where Winter temperatures can drop into the low 30's, I believe a hybrid heatpump would handle 80 to 85 percent of my daughter's heating requirements leaving only the coldest days for the natural gas heater to heat her1750 sq foot, two story, well insulated town house which has only two walls exposed to the outside.

My daughter has interviewed two NJ AC contractors and they both seemed very reluctent to install the hybrid system I described above.

Both contractors told her that such a setup is only used in Florida and would never work in Southern New Jersey

I live in North/Central Florida and use an Infinity heatpump with a three stage auxilary electric heatstrip installed in the air handler.

I have friends who live in a nearby community, who have an AC and use a gas, hot air heater instead of heat strips for backup.

I don't understand why a hybrid heatpump with a matching natual gas, hot air back-up heater is not a viable alternative in the sourthern part of New Jersey.

Any and all comments are welcome. Bill.

 

We call those gas packs where I'm from, to distinguish them from heat pumps. They work fine in Middle Tennessee, and here in Northern Virginia. In fact, the colder it gets the better they are, compared to a standard heat pump, with its electric back-up heat.

 

Nashkat1 told it like it is. A Gas packaged unit should work great for her. The only difference is that the Northern temps are much more frequently below 40 degrees where a air exchange heat pump becomes ineffiicient. She will be on the gas heat much more often than you experience in Florida, but she should still benefit from a heat pump in the milder days. What she DOES NOT want is her backup heat to be electric heat strips, they can devastate your heating budget in a short time. We have a neighbor who, during a cold snap of three week duration last season, had his electric backup heat strips come on almost every run of the machine. His $1100 monthly electric bill taught him the lesson about heat strips. She needs to talk to a Carrier dealer with experience about this package. I also do not understand why an installer would balk at this install.

 

Hi thanks for the prompt, and informative replies. This it the first I have heard of Heat Packs.

After checking the Internet to learn more about Heat Packs, I don't believe a Heat Pack will work because a Heat Pack which includes a gas heater and and a heatpump are located outside in one unit and requires access to the duct work inside the house.

The AC condenser at my daughter's town house is located outside. However, the gas, hot air heater is located on the first floor in the center of the house so there is no practical way to access the ductwork from outside.

I found this statemant on the Carrier web site. "Carrier heat pumps are central air conditioners that can also heat your whole home. Paired with a gas furnace, they offer energy-use options and extra heating options…we call this combination Hybrid Heat."

So, based on the Carrier's comments, I guess Carrier believes a split system, using a heatpump and a separate gas furnace in place of an electric strip as backup heat for lower temperatures, is a viable option.

Hybrid systems have been around for awhile, so I was really taken back when two NJ AC contactors attempted to convince my daugher not to install a hybrid system with the justification that they only work in Florida. Something is not adding up.

I Think I will call the AC contractor who installed my Inifnity heatpump in Florida a year ago and see what he has to say.

Thanks again for your comments and introducing me to Heat Packs.

Bill


Bill

 

Dual fuel is a very good option in cold areas with a reasonable electricity rate.

[{{A heatpump with electric backup is only a good choice if the price of electricity is under 6 cents per kwh or there's no gas available.}}}

In dual fuel setups, the furnace takes over completely when the heatpump can no longer keep up (A dual fuel thermostat and outdoor temp sensor take care of the changeover); wheres, heat strips in all electric systems only provide supplemental heat.

The temperature at which heatpumps can not keep up any more is called balance point, which is function of the heat loss (of the house) and the size of the heatpump. In most applications, the balance point is between 25 and 40 degrees.

The capacity of a heatpump matches its cooling capacity at 47F; the colder it gets, the less heat they put out.. Contrary to the info posted in this thread, modern heatpumps don't "become inefficient" at 40F - they can provide heat very efficiently down to 17F or lower.Capacity is the limiting factor much more so than efficiency.


In order to determine if dual fuel is a good investment, the following information is required...

- The cost premium of a heatpump (...and associated controls) over the equivalent a/c
- The total cost of electricity (including distribution and taxes)
- The total cost of natural gas (keep in mind that the price of gas is very volatile)
- Heat gain and loss of the house (load calculation required)
- The balance point - calculated based on the size of heatpump required and heat loss of the house
- Average number of days per season above the balance point

In general, if only 4 weeks per year are above the balance point (in the spring and fall when heating costs are low to begin with), dual fuel isn't worth while.

Never ask a contractor to do something that he's not comfortable with. If your daughter decides to get a heatpump and furnace, she should use a contractor who has successfully installed many dual fuel systems .

In florida it makes sense to install heatpumps with electric backup since it rarely drops below freezing there.

Dual fuel gives the best of both worlds; the efficiency (and less intense heat) of a heatpump in mild weather, and the capacity of a furnace below the balance point.

 

Your daughter has one of the most common heating and cooling systems: A central gas furnace with an outdoor condenser and compressor connected to a heat exchange coil located in the supply plenum of the furnace, with the blower and ductwork serving both heating and cooling.

Some points you may want to share with your daughter:

• The best approach is almost always to replace all three system components at once, with equipment from one manufacturer and one contractor;
• Have the would-be contractors specify the BTUs of their proposed furnace, and the calculation it was based on. She should look for proposals that suggest a unit slightly larger than her existing one;
• The highest-efficiency furnaces look and sound sexy but are seldom a good investment - unless she is planning to completely redo the doors, windows and insulation in her house;
• The outside unit that is the best fit will probably be slightly larger than the one it is replacing - by 1/2 ton or so;
• The heat exchange coil should be matched in capacity to the condenser;
• Keep an eye on the ease of replacing the filter, and on a clear path to drain for the condensate off the heat exchange coil;
• If she includes a 7-day,4-event programmable thermostat in the upgrade, and makes sure that it is tied to power and only uses batteries as backup, and if she carefully thinks through programming it, she can have a wake-up call and a bedtime prompt as extra benefits, she can expect some significant utility bill reductions, and she can basically have a set-it-and-forget-it system.

 

I contacted my Florida AC installer today. We chatted for approximately 45 minutes about Carrier, Infinity, hybrid systems.
He was shocked that two AC dealers in Southern New Jersey would be hesident to installed a Hybrid heatpump system.
He said there are two ways for my daughter to go.
She could have an Infinty heatpump installed along with an Infinity gas heater. The gas heater would take the place of the electric heat strips in an air handler. The system would be managed by an Infinity Controller which would orgistrate the heat pump, gas hot air heater and the AC seemlessly.
He continued that a better way to go would be spend a little more money and purchase a heatpump that Carrier just introduced. It is an Inhanced Infinity heatpump with Green Speed Intelligence. He said the new Green Speed heat pump is so efficient it will heat her house down to single digit outside temperatures without the assistance of a backup heater. It does this by running the variable speed, scroll compressor at a higher then normal speed. He said Carrier has Green Speed heat pumps running in Indiana that are heating homes without the assistence of a back up system during the entire Winter. He continued, the nozzle temperature of the GP units is typically 128 degrees F. Much higher then a typical heatpump.
He suggested the best way for my daughter to go is to install an Infinity, Green Speed heat pump with a mid (80%) efficientcy Infinty gas heater. The gas heater will be used so infrequently, the pay-back period on a high ultra-efficiant gas heater would be too long.
Important things to consider. Duct work static pressure should be preferably 0.5"wc but no higher then 0.7"wc. It should be measured before the installation begins.
Because the copper refrigerent tubes cannot be replaced, it must be determined if the existing tubing size is compatable with the 3 ton Infinity heat pump.
I am certain the Green Speed unit will be expensive but Carrier usually offers a substantial rebate on high end equipment in the Spring and Fall. Plus, there is a $500 FIT credit available.
The energy savings are estimated to be in the range of 50% considering she will be replacing a 20 year old, 10 seer AC unit and 20 year old natual gas, hot air heater.
So now the problem is to figure out how to perswade my Florida AC dealer (a GREAT guy who runs a GREAT company with compentent and friendly technicians who are willing to talk to me for 45 minutes on the phone knowing there was nothing in it for them), to travel to New Jersey to install a new hybrid heatpump for my daughter. Bill

 

Storage water heaters are only around 60% efficient give or take 5%.

It's in her best interest to replace the air handler and hydronic coil with a normal furnace.

That's incorrect on several levels.

The higher the heat loss of the house is, the more money a high efficiency furnace will save.

If the house has no insulation and needs 100 000 BTUs of heat per hour on the coldest night of the year...

A mid efficiency 80% eff furnace would need to burn 125 000 BTUs/hr worth of gas to provide the heat required. (that's 25000 BTUs per hour right up the chimney - equivalent to wasting the heat produced by five electric space heaters running on high)

A basic 90% efficient furnace would need to burn 111 000 btus/hr worth of gas to provide the heat required.

A top of the line 95% unit would only need around 105 200 btu/hr worth of gas to provide the heat required.

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For the record, the only difference between a mid and high efficiency furnaces is that 90%+ models have a secondary heat exchanger. (well, along with the ability to use outdoor air for combustion) The controls, electrical and mechanical parts are basically the same - in fact, the circuit board is often identical.

The price premium for a basic high eff furnace is only $500-$1000; hence, the return on investment in a colder climate can be well excess of 15% per year.

There are more expensive models available which have 2+ stages of heat, high eff variable speed blower motors, etc but they cost more to purchase and repair.

In Canada, mid eff units aren't even available any more, and if they were - very few people would buy them.

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Heat loss should always be reduced if possible prior to installing a new furnace for sizing purposes, be it mid or high efficiency. New windows, doors, and wall insulation may not be a good investment, but air sealing and adding attic insulation can have a decent return on investment.

 

Sounds like you have an excellent contractor - most probably don't even know what static pressure is.

The greenspeed I believe is top of the line (as is the infinity furnace), so the total installed cost with a furnace could be well in excess of $10k. The cost of future repairs could be very high as well.

A careful cost benefit analysis should be done to determine what type of equipment should be installed.

 

I'm in NE Indiana and install hybrid (dual fuel) systems all the time. Dont get stuck on just carrier contractors/systems. It matters much less about brand as it does proper installation. In my previous home (5 yrs old) our HP (13 seer) balance point was 15F. It all depends on the home and equipment sizing and installation as to how a system will perform.

Green speed HP's are salty! The technology is so new that carrier can charge a hefty premium for those systems.

I would never replace a furnace in NJ without upgrading the efficiency to 95% if using a NG furnace. They are not much more expensive than mid eff units. We don't even offer mid eff units unless there is an installation complication or the furnace is in a location where freezing temps will occur.

 

nvactechfw Forum Topic Moderator.

At what efficiency level does a natural gas furnace require an outside air feed for combustion? My daughter's natual gas furnace is on the first floor of a two story townhouse with no convenient way to access the outside. So, it may not be possible to go with a high efficiency furnace that requires an outside air feed. There is a combustion vent pipe that is routed to the attic that may provide access to the outside through the attic. I will have to investigate that possiblity.

Unlike Northern New Jersey and New York, southern New Jersey (near the Del. border) typically has mild Winters. That is not to say it doesn't get cold but usually not for long periods of time. They do have a fair amount of gray, overcast, damp periods with temperatures typically in the high 20's and low 30's. Recently, the Summers have been in the mid 90's with some days in the triple figures.

Approximately two years ago, I replaced a Trane HP at my home in Florida. Because I had 16 years of trouble free service from Trane, I started getting estimates to replace my HP from local Trane dealers, not even considering other manufacturers.

About that time I started asking questions on this Fourm. Because of the advice I received from Forum members, I decided it would be prudent to interview other HP manufacturers. I was impressed with one Carrier Dealer (I interviewed 3) who went into my attic to inspect the duct work then used a magnahelic gage to measure the pressure in the ductwork with my HP running.

After that, it was pretty much a matter of comparing Carrier Infnity with other units.

I was open to other manufacturers but after at least six interviews it came down to Carrier and Trane. After spending many hours comparing the two units, it became apparent to me, at that time, Carrier seemed to be is at the top of their game.

One turn off was the fact that the top of the line Trane HP was using two compressors and Carrier was using a two stage compressor that could change speed on the fly.

The hard part was deciding on a dealer. I decided to consider only factory autorized dealers who used factory trained technicians. Most large dealers in this area are big operations who do a lot of new development type installations. Some of the big dealers examined my duct work but only Summa A/C & Heat located in Eustis, Florida took the time to answer all my questions and actually measure the air duct pressure. The "salesman" seemed more like a technician then a salesman and I related to that probably because he could answer my more technical questions about both the equipment and the installation. And in addition, gave me the best quote and handled all the rebate forms.

After living with the new Infinity HP for nearly two years, I am extemely happy with the Carrier Infinity HP and the dealer I selected. He is not the largerst dealer in the area but as far as I am concerned he is the most competent. He paid attention to detail, was willing to take the time to explain what he was doing and why he was doing it and left nothing to chance. I am certain other dealers would have considered me a pain in the ass but I never got that feeling with this dealer.

Bill

 

Most 90%+ efficient furnaces can pull combustion air from outside, but pulling air from inside is optional.

It's always better to use outdoor air for combustion.

All 90%+ models vent through 2-3" plastic pipes, so if there's no way to run new venting, she'll have to get a mid efficiency model.


How much does electricity cost in her area?

 

I am not certain how much she is paying for electricity but I will try to find out. Bill

 

I wonder if is would be possible to run the PVC vent and intake air PVC tubing inside the existing insulated flue pipe which runs to the attic and thru the roof? Bill

 

This is a really great thread, my HP is 12 yrs old, keeping this for future reference My house has NG currently being used for HW and Fireplace. Seems like a great option.

 

A couple of thoughts:

Ductless mini-split heat pumps are now availabe with temperature cut off points well below 18 degrees Fahrenheit. What is the temperature cut of point for a cold climate air source heat pump these days? If the cut-off point is really low she may be better off to go all electric.

She will pay at $20 per month just to have a gas hook-up at her house. If she does not have any other gas appliance in her home she can save $240 per year to shut off the gas connection to her home.

Auxilliary heat - is there any additional heat source in the home?

System cost. A gas furnace and a separate airconditioner will be the most expensive option to install. The heat pump system with electric the least expensive to install. The hybrid gas/electric will be on the upper side in expenses.

System choice. There should be savings if she bought the equipment (whatever she wants) from a wholesaler direct. I have bought Goodman furnaces before. It is a DIY brand. The equipment works well and she can save up to 30% on equipment cost. There is so little difference in quality between manufacturers these days that it really should not matter. She could buy the system online and get someone to install it locally. If there is not a time rush she can get a great deal.

In general I have not seen that much in additional savings by having a gas/electric system installed. If there are significant periods during the year....let's say 2-4 week time periods at a time with extremely cold temperature.....it may make sense. If it is just a few days here and there....not sure whether it pencils to have a hybrid system.

 

I agree with you hvactechfw - don't get stuck on a manufacturer. Choose the best system set-up and get a good installation.

Your Florida AC dealer won't be licensed to do an installation in New Jersey. ;-) Nice try.