Fear of (Dual) Fuel
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.
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.
Dont listen to that guy, he just doesn't know how to install a unit properly. Dual fuel units are great, you get the efficiency of a heat pump in mild weather and the efficiency and warmth of a gas furnace in colder weather. As far as a hp compressor lasting 10 yrs he obviously doesn't use correct installation practices bc it should last 18-20 yrs. we have customers with hp's that are 30+ yrs old, of course they don't make stuff like they used to though
As long as the duct system is sufficient for the size unit a variable speed blower motor will be fine. Make sure these contractors are using manual j load calc. Your new windows will reduce the size that your old system is and any other upgrades you have made. Get a blower door test done on your home to see how you can fix your house/duct system to accommodate a smaller unit. Less up front cost and less utilities with a smaller unit
Sounds like he isnt familiar with the newer systems and people usualy bash what they dont fully understand. Going with a heatpump when you are used to gas only heat you may notice that the air feels and is cooler coming out of the registers. However it is still heating your house correctly and at the point it cant handle the load the gas will come on. We have had customers new to heatpumps that complain the air is not hot enough and want to adjust aux heat (gas or electric) so it runs more, which negates the benefit of the heat pump. Mind the thermostat/home temp not air temp.
My company regularly services 20 and 30 year old heat pumps all the time, they should last just as long as a straight AC. He is somewhat correct that it will low out slightly cooler air than a furnace, but you can always change the temp at which the furnace kicks on instead of the heat pump and depending on size of heat pump vs heat load vs outdoor temps, I don't notice the air being cooler except maybe 5-10% of the time at most.
I would 100% go heat pump and that is what I use backed up by gas at my house. I agree with others this guy just does not know how to properly set a heat pump up so they bash a technology that is more efficient than AC and furnace.
I would definitely turn away from this indiviDUAL who may be afraid of his own skin.
Originally Posted by AZag
A customer can "operate" a dual fuel system if one can arrange for an annual service agreement, set a thermostat and pay the gas & electric bills.
A switchover point of about 34' F to gas furnace should be more than sufficient to keep you feeling Very Comfortable.
mid-December - January - February will have a few 100's hours of run time on the gas furnace.
But, the rest of the year would be very limited.
H.D.D. 3,400 Heating Degree Days
C.D.D. 2,000 Cooling Degree Days
The only discomfort I recognize here in this individual's LACK of experience in properly setting up hybrid systems.
How much are your electric and gas rates? Without knowing these it's impossible to determine if dual fuel makes sense or not. In our area it does NOT make sense since NG is so cheap compared to electricity. Our gas company builds the delivery charge into the $27/mo meter fee, but only charges 40 cents per therm of gas. Electric rates are 6 cents per KWH in winter for use that exceeds 600KWH per month. Dual fuel systems were popular 10yrs ago when gas prices jumped up, but now the people who own them just use gas. Once you feel the warmth of gas heat it's hard for most people to go back to using the heat pump.
You need to know the costs of fuel in your area to determine the balance point where your system goes from electric to gas. From what I've heard electric rates in the NE part of the country are very high compared to NG rates, so much so that natural gas dryers are used almost exclusively.
Heat pumps can last less time than straight a/c, the compressor will be running more often, and in harsh conditions. yes, there is more complexity to a heat pump... I find it hard to understand a tech that would have difficulty with that complexity though... yes, there is a lot more going on with a heat pump, or a 2 stage system, variable blowers also have their issues.
which is why it's most important to get a company that can install this equipment PROPERLY and SIZED CORRECTLY for your home.
that company, or possibly just that salesman is used to selling basic equipment, and is skiddish from problems of his installs... I'd simply remove his info from my list of candidates, maybe hire another few guys to quote the install, and make the decision from there.
our area of the country makes dual fuel a wonderful choice, great heat in mild weather with little hit on the wallet, and wonderful heat in bitter weather.
2 stage gives great dehumidification, and still handles the heavy heat of the summer... variable speed blowers make efficient use of the blower, and match perfectly the dual loads... and great filtration of the house with low costs...
I agree with all the naysayers who think the tech was giving you advice. If nothing else, dual fuel gives you choices. If there is anyone out there who can predict the costs of heating with natural gas vs electricity over the next 15-years or so, I'd like to meet that person so I can also advise my clients on the wisdom of installing dual fuel.
IMO, that's the only reason you'd need to exercise the option of dual fuel or not. As far as the comfort is concerned, since you're already getting a modulating gas furnace, you'll grow accustomed to the introduction of heat over the long term of time, rather than short bursts. This will improve comfort and you'll get the same results from a properly sized HP as you will from a properly sized furnace. Yes, the register air is a little cooler but the room is the same temperature either way. So don't fret about register temps unless you favorite easy chair is directly affected by one!
You stated that you've selected infinity equipment with a user interface. That makes the hydrid heat/dual fuel system integration as simple as it can get! Well, that is, for an educated technician. And the entire system, whether straight cooling only or dual fuel, comes with a 10-year parts warranty when registered within 60-days of installation. 2-Stage cooling equipment is, as you've accurately described, superior to a single stage system due to longer cooling cycles, which results in better humidity control in summer. It also uses less electricity when either heating or cooling on 1st stage. And yes, the dual fuel system is ecologically friendly as well, producing less pollution when the gas furnace runs. FYI, the HP used for Inifinity systems now is the Greenspeed HP, which can be sized more for heat and still be excellent for cooling with humidity control due it's ability to operate at greatly reduced capacities when necessary. I don't know about your area but in ours, a company cannot purchase that HP until they've been trained on it.
So in summary, I'd highly recommend finding a company that performs an accurate load analysis for proper equipment sizing and is comfortable with multi-stage or better yet, modulating cooling, dual fuel (hybrid heat), modulating heating, Infinity or Bryant Evolution (same products) products and you should enjoy great comfort.
Pay close attention to your third dealers statements in reference to air distribution to the top floor with two stage, and modulating furnace system not being able to deliver air to the top floor. This is one item that gets overlooked when two stage/modulating equipment is installed on existing systems.
Originally Posted by AZag
As fare as duel fuel in the Washington Metro area, it is a great choice, if installed and set up properly.
$1.15 / therm ... 100,000 BTU/Hr
Originally Posted by skippedover
$0.133 / kW-Hr ... 3,413 BTU/Hr
$3.90 / 100,000 BTU/Hr
_ / 3 COP say at > 32'F
__ $1.30 / 100,000 BTU/Hr
" THE WIZARD OF OZ"
may know the relative costs of Natural Gas vs electricty a decade or two out.
Sounds like that contractor doesn't really know much about dual fuel systems, or 2 stage systems.
Duel fuel is a nice option especially on mild days where you just need a little heat to knock off the chill .when it gets cold you can always just turn the tstat to emergency heat and it will run on the gas furnace only.