Dak

Not a fan of Lennox heat pumps and it's possible dual fuel may even be overkill for your area/climate.

However I don't think a high eff furnace is necessary because of the usual moderate climate.

I would go with the 80% two stg var speed SL280V furnace or similar of another brand. Link attached.

IMO

Here is a link that might be useful: Lennox SL 280v furnace

The US DOE has worksheets that can help you calculate relative costs with your current prices of energy.

normally I would say heat-pump (since a heatpump doesn't cosst much more than straight A/C), but since you don't like the comfort because its a leaky house I can understand getting the furnace.

Heatpumps don't do as well in leaky older homes.

Will you explain the logic behind this statement:

"Heatpumps don't do as well in leaky older homes."

No heating or cooling equipment will "do as well" in older or leaky homes as in well-sealed homes. Heat pumps are not unique in that respect.

True, no heating or cooling system does as well in a leaky home. However since more btu's are required to heat a leaky home, a heatpump may be running constantly to maintain desired temperatures in colder situations. It sounds like the original poster is experiencing this situation already. For them I recommend the gas-furnace for there leaky home.

A BTU is a BTU. It does not matter if it is generated from gas or from a heat pump. If a 50,000 BTU furnace is running constantly to heat a home so will a 50,000 BTU furnace. Why are you writing these misleading things?

Well furnaces are cheaper to oversize and also OP lives in an area where cooling dictates HP size. So the furnace may make more sense despite the fact that a BTU is a BTU.

Is this correct? A leaky house will require lots of cooling capacity. Since cooling dictates HP size in that climate, there will be excess heating capacity if the correct size HP is installed for cooling.

HP or gas, all other things being equal, should be chosen primarily on current and projected fuel costs. The latter will be hard to do. Is your crystal ball working?

Leaks matter a whole lot more in the cold. The ACH is higher in the cold and the delta T is a whole lot higher.

I guess I am stupid. I am still not seeing why BTUs change depending on temperature differential or ACH. Maybe someone can explain in simple terms.

A gas furnace will put out (lets say) 50,000 BTUs at whatever temperature the outside air is. 50k at 70f. 50k at 40F. 50k at 20F.

A HP will not do this. The lower the temperature, the lower the BTUs produced. At some point it cannot produce enough BTUs to heat the house. Leaky houses are worse in that the point is reached sooner.

Also it isn't that BTUs change but I'll give an example. A leaky construction might have a 5,000 btu heat gain in the summer but a 15,000 loss in the winter.

Best construction assumes .2 ACH in the summer and .3 in the winter. That is a 50% increase in air exchange. Then if in summer it is 90 degrees outside and 78 inside, that .2 ACH an hour will not gain that much heat. But have it be 30 degrees outside ... that is a lot of loss.

That is why it matters more for heating and then what weedmeister said.

I guess I misinterpreted, "Since cooling dictates HP size in that climate". I read it to mean that if the HP is capable of cooling the house, there will be more than enough capacity to the house. I guess what it really means is that the HP will be big enough to cool the house, but when it comes to heating, you might have to design in supplemental heat.

Have I been fooled? I thought that the best quality modern low temperature heat pumps can deliver upwards from 90% of their rated capacity at 5 F. What % of heating, at average winter Orlando lows (50 F), do "standard quality" heat pumps deliver at record lows (20 F) in Orlando?

It would be nice to hear back from OP dakflorida.

Because of OP's location and climate plus the fact that the cooling season can be long while the heating season is much shorter, I think an 80% eff two stg var speed furnace paired with a high eff AC condenser sgl or two stg is the best choice.

For the previous comment, AHRI HP directory lists heating BTUs at both 45 degree and 17 degree for all certified matching systems.Suggest you go to AHRI HP directory and look at some of the better HP models like Trane and Carrier to get an idea of both performance and efficiency. It's definitely not 90% of rated capacity at 5 deg fah.

IMO

I am surprised that there is such a concern about the cold season given that the poster lives in Orlando, FL. I would think the winters are moderate at worst and the 40 degree weather would not last for too long. While a heat pump may be less efficient during those few weeks of 40 degree weather, I expect that would be more than offset by its greater efficiency during the rest of the year, not to mention the cost savings relative to separate furnace and A/C units.

Here is a link that might be useful: HVAC Site