I'm still trying to figure that one out. I am having the same problem. I have replaced the blower motor, replaced vaccum lines, everything works. I have hot heat but not blowing enough out. I'm going to try to back flush it.
One.
It's called water heater. There isn't a reason to heat hot water
You should check your thermostat and maybe your water pump,catalitc converter, heater core, hoses might have holes in them or maybe low and colant
a bad water pump could cause low heat. The heater uses the coolant from the pump to generate heat.
There are two insulated heater elements that heat the water.
the heat output is reduced
Low water in the radiator will result in no heat. The water level is not sufficient to reach the heater core. The heater core will become cold.
More than likely you will not have heat being the water wont be circulating through the heater core , When the hot water passes through the heater coil the air passing through the heater coil makes heat blow out the vents when you have selected a heat setting on your controls.
If everything on your car ( thermostat, heater core, heat controls, water pump) has been changed and you are sure that it all works, check the water flow. A clog or an air bubble in the heat lines will cause coolant to not flow and have no heat output.
It is to heat water for some purposes.
A Heat Pump while more expensive to buy than a gas heater has much lower operating costs. It is also much cheaper to install requiring only an electrical connection instead of a gas supply line.
With no water no heat can be transferred through the heater coils.