I've worked on lots of cars so one would think this would be a piece of cake, however there are some things that don't add up with this issue.
Bought the car from a Honda dealer, a one owner with 85K miles on it. I drive 25 miles to work and the heater gets quite warm but not hot. Had the dealer ck it while in for it's first free oil change, they said all was normal.
Yet I think not. I live in SW Michigan and now it's getting cold, in the 20's. After the gauge shows the car is warmed up, the heat works, but doesn't get hot enough. Unlike all other cars I've worked on the thermostat is not on the top of the engine? Instead it's mounted on the bottom radiator hose near the lower part of the engine. The section on the engine side gets hot, yet on the side towards the radiator the hose is dead cold, no circulation happening. Yet the engine gets hot enough to kick on the cooling fans, and the coolant circulating through the heater hoses at the firewall seem quite hot, It appears the thermostat is stuck closed, so you would think the engine would get hotter than normal, but I don't know what the circulation path is to the heater. I.e. does minimal coolant flow through it until the thermostat opens then it gets full flow. Second since the thermostat doesn't appear to be opening, why doesn't the engine overheat, I've drove it though the summer with the a/c on and the gauge never showed hotter that slightly below half way. Thanks for any tips or insight you can offer.
Update: Removed the thermostat and boiled it, it does open and close at what appears to be the correct temps according to the service manual. Could the fans be kicking on prematurely or does this engine ever have issue with air trapped in the cooling system?

 

You're getting hot water to the heater core but not getting heating. Most likely the problem is the air mix motor/s are not working. Suggest inspecting air mix motor movements (driver's and pax) as temperature setting is changed.

If these are working correctly, smooth movement as temp setting is changed, then heater core may have a blockage preventing adequate flow through the heater core. This would require a reverse flush to clear. See youtube video by ChrisFix on flushing heater core.

Not sure what to make of lower radiator hose staying cold w/ normal operating temperature. Very low coolant flow might have this effect. Mercifully I don't have a lot of experience w/ very low outside temps.

good luck