IS DUAL FUEL HYBRID (heat pump + gas) STILL REQUIRED?

On June 29, 2023, Steve Miller asked for input on whether dual fuel heating systems are still needed in NJ, considering newest technology high efficiency cold climate heat pumps.   He provided the following statement:. 
Dual fuel – heat pump plus backup fossil fuel furnace - is often still being proposed by HVAC installers in cold climate states like NJ.   The alternatives might be:

• Weatherize the building, to reduce the heat loss- makes it easier to find a suitable cold climate heat pump
• Locate a cold climate heat pump that can supply nearly the entire heat load (BTUs per hour) at the design temp. Design temp- (typically near 10 degrees F in NJ) is the regional lowest temp (99% of the time), when heat pump + auxiliary heat output is equal to the heat loss for a particular building,  This temperature would also be called the balance point)

For additional heat in case temps drop below design temp for a particular building, options might be:

• Install larger sized electric strip heating, instead of gas, for required heat on exceptionally cold nights (this is a system design decision based on tradeoffs in emissions, energy efficiency, and cost)
• Maybe residents would not know or care there is an overnight small drop in home temp, because the deficiency is  quickly corrected  the next morning. 
  This was tested in a Maine trial this last winter, where backup heat was disconnected in trial customers.  Preliminary results revealed few or no complaints.
• Also, 17K customers in upstate NYState were equipped with a heat pump with no backup. Followup revealed 20 complaints (of various types) (~0.1%) Source: Matt Christie, Director, TRM Advanced Residential Building Decarbonization, Feb 15, 2024 "Heat Pump Technology and Market Primer" video 12:30 to end; slides & comments

REPLIES to the above question "Is Dual fuel required?"
Chris Wisniewski, Principal, Integrate Comfort Systems (866) – 749-6331 ext. 701 chris@icshvac.com  6/30/2023

• Yes, especially crucial in very old and poorly insulated buildings. May not be as big a factor for post 1990 construction
• Yes – depends on what your definition of “economical” is. For us the electrification of a systems heating home means you have to have a dependable and reliable system – I think most agree that heating is crucial in our climate and its not just there for comfort like AC – your home could get destroyed if you don’t provide heating. So choosing “economical” equipment may be a weak link for the long term. We only use Mitsubishi cold weather heat pumps that have a track record of performing and reliability. We have used others that do not have the same track record. The systems I would not say fall into the “economical” category – they are the standard of the industry
• There are many factors to this, but in a perfect design you do not need additional sources of heat. A cold weather heat pump can manage all of the temperature ranges we experience in NJ. However you can use any supplemental source that makes sense:
• Electric heat – perfect for small capacity gaps and perhaps infrequent use – it has a low upfront cost
• Hybrid setup using a gas furnace – this is great when the heating needs of a home are great and perhaps one heat pump does not have the full capacity to heat the house. You get the best of both world – there is still a huge benefit to probably running the heat pump  50-70% of the winter

William Amann, President, M&E Engineers, 7/6/2023
Here are two of many technical concerns

• There is an inherent delta between heating BTUH’s and Cooling BTUH’s for many buildings because the winter Delta T (70-0) and summer Delta T (95-75) are so different. The right-sized heating system can be over-sized for cooling.
• Strip heating is typically controlled by a local thermostat so it may operate a lot (occupant may not be aware), and not just when the outside temps are real cold.

July 12, 2023 Video: Dual Fuel Heating Systems - Advantage or Compromise?; Slides panel discussion hosted by Electrify Now;:

Panel speakers listed below: