1988 Manufactured Home Needs New Furnace and Water Heater

Manufactured housing has special requirements for their fossil fuel burning appliances. the combustion air for the burner MUST come from outside of the enclosure. There are no oil fired boilers that make DHW that fit that criteria. However there are several oil and gas fired appliances designed for space heating that should be an exact fit for the duct opening where the old oil fired furnace was removed. There are also gas fired water heaters designed for manufactured housing. (Now we are talking about single wide and double wide one story manufactured housing where you leave the wheels under the actual building.)

If you are talking about Modular Homes that are built off site then 2 to 6 pieces are delivered to the site and a crane puts the pieces in place,on a prebuilt foundation, that is a different story. Modular houses and Manufactured houses are two different animals.

Nordyne has some options for you. Miller was a very popular furnace choice for manufactured housing in my service area. https://literature.nortekhvac.com/Miller/Gas_Furnace

Um… well, I wouldn't have said Sullivan County was particularly far north, nor particularly cold — being well south of much of the State. Your design temperature is plus 3 F, and that is warm enough that a good high performance cold temperature heat pump should work. Mitsubishi hyper-heat units claim to work well down to - 5 F, for instance. So don't assume that a heat pump wouldn't be suitable.

On your question 1 — a lot of people can't do arithmetic. With oil for you at $4 per gallon, the LP would have to be less than $2.70 per gallon to get the same heat for the same price. LP doesn't have the heating value per gallon that oil does.

1. I also agree with Jamie. If you have Natural Gas and compare it to your highest fuel oil bill they got in the winter, there may be a savings. However some folks look at a 2 to 3 months supply of fuel oil at $600.00 all at once and then compare it the the natural gas bill that comes in monthly and see that the highest bill is never over $200.00 (or something like that) and jump up and down to say that gas is cheaper. OR, someone who took out a 70 year old coal converted to an oil heater that operates at 60% or less efficiency, and compare that bill to a brand new medium to high efficiency gas heater and say that it saved them lots of money. But that is with Natural Gas. LP Gas is delivered just like Oil, from a truck. and the amount of energy measured in BTUs for a gallon of LP Gas (91,000 BTU) is a lot less than the amount of energy in a gallon of fuel oil (138,000 BTU). So when you have a choice between Oil and LP Gas of the same efficiency, Pick the oil heater.
2. A tankless gas water heater will cost less to operate than the electric tank water heater you removed.
3. YES you connect the package unit to the same ductwork. you use a collar made specially for mobile home duct work that prevents back draft thru the outdoor unit, from the furnace inside that will operate in the winter. You must also install a special damper made to be placed under the new furnace to prevent back draft in the summer. If you get a package unit that does both heating and cooling then you don't need that damper because you eliminate the inside furnace and just cover over the furnace opening with a sheet of metal and some mastic, then insulate over it.  That is how you get the extra space inside.
4. Package unit is most definitely a DIY job.  The unit comes pre-wired and set up so you do not need to bother with refrigerants and for the most part, if it is already set up for LP Gas, then you can probably plug and play.  I would have a professional from your gas company come and check your work to see that the flame is burning properly with combustion instruments.  If you need to use a conversion kit to change the unit from Natural gas to LP gas, then you definitely need to call the gas supplier to do the start-up.  You also want to save the Natural Gas parts from the conversion.  You never know where that package unit is going to end up and if there is natural gas, you want that for sure. 

I don't know of any combination units fired by LP for heat and also providing AC — at least not all-in-one type things.

Your furnace cycle times tell you a lot more about the insulation in those mobile homes — which is probably pretty close to non-existent (at least the ones I've encountered were a little weak on insulation…) than they do about the furnace efficiency.

How cold does it get in the coldest months? If it doesn't get much below 10 F above, have you thought about possibly installing a heat pump? Might require a wiring upgrade… but it would give you AC as well as heat, and depending on your electric rates would be competitive to run. More expensive to buy.

1,000 square foot? I'm guessing a 70 by 12? The size furnace you need depends as much on where you are located (how cold it gets) as anything else.

One thing to consider: mobile home furnaces, in general, are slightly to significantly to a furnace for a regular house. It needs to fit in the space provided — which is usually pretty cramped — and still be serviceable. Most mobile homes (not all) also use a downflow furnace design, rather than upflow or horizontal which is more common in a stick built house, and may need more powerful blowers. Furnaces designed for the purpose, however, are easy enough to get.

Without knowing your heating requirements and how the present furnace is installed and ducted I can't get much farther for you.

Here is a standard manufactured home double wide duct system

I have added the package unit and the flex duct connections to the supply and the return.

A single wide duct system is about the same except you just connect the supply to the bottom of the single trunk duct near the old furnace location.