I've got a few related questions that have been driving me mad. (my wallet too)

A few notes- The house is mostly gas. No programmable thermostat or double pane glass.

My heat at night is set below 68 (usually around 65) and it seems to run all the time with very short breaks. I put my hand to the vent when it turned on and it was NOT blowing "hot" air. Not cold but coolish/warm?
We change our filters about every 45 days. We have heavy drapes, insulated our leaky outlets, added ceiling vent deflectors, close off rooms and run ceiling fans clockwise on low... we seem to be doing everything possible other than the high ticket items but the heat at 65 comes on every 5-10 minutes and blows coolish air.
The odd thing is... If we crank it to say 71 or 73.. the rooms get warm indeed. Thought no matter what the setting..it should always blow the same temp of air???

Any help is appreciated!
Sorry it's so long. :)

My thoughts hear is, since the house is so poorly insulated and the thermostat is set at 65/68, that when the forced air blows, it takes longer to heat up the house because the ducts were colder on the initial start up. The forced air takes longer to heat a colder duct than a pre warmed duct. That's why it seems to run better at 71/73. The duct starts warmer and seems to run shorter to feel that heat change quicker.

To get a better picture of that think of the car and how long the initial length to heat it up. Warm the car and drive it for some time. Park let the air in the car really cool down and restart it. It heat quicker because the dash etc is warmer on the re heat even though it dropped in air temp. The car heater didn't have to heat the heat ducts because the had a life of there own and became a warm rock overnight

Heating colder furniture and floors takes a lot longer than if they were warmer on the start.
The base temp of 65/68 just warms up the house air and the solids materials are dense and the stat kicks off before the cold environment the duct started in

The bottom line hear is insulate the ducts better. Check ducts for air leaks in the basement that can loose the heat before it get to you.

A low ticket Item that can be done is steps is insulate the attic or what ever is above the ceiling with Unfaced Insulation. While you are up there check to see if the insul is faced the wrong way with the vapor barrier facing you as you look from above and it should be on the warm side against ceiling below you. Don't add more insul directly over a vapor barrier

How to Inspect Building Interiors and Building Insulation/Ventilation

How to Inspect Building Interiors and Building Insulation/Ventilation

Signed 21 Boat

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My heat at night is set below 68 (usually around 65) and it seems to run all the time with very short breaks. I put my hand to the vent when it turned on and it was NOT blowing "hot" air. Not cold but coolish/warm?

If you want to test the temperature of your air discharge and be accurate you need to take the return air temp and the supply air temp and subtract the return from supply. That will give you a ruff heat rise across the furnace heat exchanger.

close off rooms

Your system was designed to operate properly with all registers and return air paths open. You can close off registers but that can throw off the proper operation of the furnace.

but the heat at 65 comes on every 5-10 minutes and blows coolish air.

The main question is how long does the furnace operate. This is called duty cycle. On gas this figure is ruffly 6 times per hour or 6 cycles per hour.

The odd thing is...If we crank it to say 71 or 73..the rooms get warm indeed. Thought no matter what the setting..it should always blow the same temp of air???

The longer the furnace run time the warmer the room will get and the warmer the discharge temp will be. Remember the relationship I explained before?

((If you want to test the temperature of your air discharge and be accurate you need to take the return air temp and the supply air temp and subtract the return from supply. That will give you a ruff heat rise across the furnace heat exchanger.))

The differential between of the supply and return will stay the same on a properly running furnace. The differential between the supply and return (the spread of the temperature) is the critical factor.