converted school house terrible to heat

i so need help
i own a 1800 school house that ive converted into my home.ive added a upstairs ,new windows did outside siding with 1" insulation and house wrap behind the siding , installed a new high efficient furnace but my home is terrible to heat.i have no basement 18"crawl space would be accurate could the heat or cold be coming from the floor and if so how can i fix it 18"is not hardley room to get down there .also my heating duct pipes run under there and it seems that by the time it gets from my furnace to my furthest room its cooled down a lot can these be insulated and how. please help

I do not know who suggested scorched heating but the did not do you any favors.

Keeping it simple think of heating like electricity.. what is a good conductor of electric is normally great for heating copper great / Air a good insulator NOT good for heating

Hydronic cast iron or standing radiators give amazing heat and hold the heat a lot longer then air.

Lots of games can be played with hot water such as non electric zone valves to fine tune the areas you want more to keep warmer /cooler.

Good luck

Under slab heating is not a great idea as you may one day decide to carpet the area or in case a pipe should fail like many "state of the art" heating systems did the home owner is up the creek trying to get someone to make good for these failures.

Greetings autoblitz, welcome to the Forum !

Have a good Day !
S.W.

In short, your floor is cooling your house. With an 18" crawl space underneath the wood, there are undoubtedly foundation vents which (as designed) allow the nice warm winter air to circulate underneath all day and night. If you haven't installed fiberglass batting in the gaps between the floor joists, you are only doing your utility bill a disservice. I'm assuming there is no moisture barrier in any part of the homes floor. You can take the fiberglass (R19+) and stuff it along the joists. the kraft 'backed' is prefferable since it's easy to staple in w/ a air/electric stapler. then run a moisture barrier along either the ground, or the the joists, and you will have created a vastly more effective air 'envelope' who's efficiency will be much better. good luck! and have fun crawling around w/ the creepy crawlys under the house...