Re: Tankless Water Heater
Just some thoughts ...
A couple of things that need to be verified when installing these systems are ...
1 - water flow and pressure
2 - gas flow and pressure.
Since this unit was installed in the summer no doubt it functioned well for a couple of reasons. The temperature of the incoming water is typically warmer than in the winter. As you know the colder the incoming water temperature and the greater the temperature rise of heating that water reduces the output from the unit. Simply it takes longer to warm cold water .... so the flow through the unit has to slow down.
The other reason it was working well during the summer was you weren't using gas for your heating system.
In your installation instruction manual it would describe the proceedure for testing to see if there is enough gas supply and checks for static and operation pressures.
As it will describe the sizing for the gas piping .... the 3/4 is the size of connection at the unit and would be the minimum size of piping ..... but that depends on how long a run of pipe. If it's 20 feet or shorter it should be fine.
However .... this is also dependant as to the supply to the home. In other words the total BTU demand from all gas appliances would have to be calculated along with the distance of run from the meter would determine the size of pipe from the meter.
Based on what you have described it sounds as though the size of pipe is undersized to supply all the BTU demand for all the gas appliances.
Depending on what your furnace input BTU and the input BTU of the water heater and any othe gas appliance may require a 1 inch line ..... depends.
As for cost efficiency ... the unit itself is in the neighborhood of 75-80% efficient while running. So ... around 20 cents for every dollar is going out the exhaust ..... which is better than a conventional tank type.
I would suspect during the winter it would probably be a little less saving since the unit has to run a little longer to output hotwater at a slower rate.
However .... because your system doesn't sound like it running properly you will probably see less saving until it's running properly.
Hope this helps.
"" an ounce of perception -- a pound of obscure "