Hot water heater as source for "water furnace"

My son bought a new (to him) first house here in Virginia Beach. Have been helping him with various problems. I asked him how his heat pump was working.
He said it was not a H/P but an A/C. I asked him how he got his heat. He led me to the garage where his water heater has split output and input lines. One output runs through a circ pump. He said he was told that is his heat. My guess (didn't get up in the attic to see as that was not the problem of the day)
is that there is some sort of coil in his air handler and that is where the heat is coming from. My friendly Trane dealer says it is called a "water furnace" or "apollo" heat. Web search reveals those to be trade names, but mostly for ground source systems.
All in all, it looks expensive to operate and inefficient. Can anyone give me a SWAG on what this is and where I might get more info.
TIA
Roy

heat

Using a water heater as input for a heating system is an inexpensive installation, but can be expensive to operate unless the house is in an area that does not require a great deal of heat. Using a water heater that way will reduce its service life considerably, and the entire heating system has to be made with that heat source in mind, because unless it is a closed system corrosion will be a factor when using "fresh water" to circulate through the heating coils if the system was designed for use with a conventional boiler.

There are units out there like the Polaris which are high efficiency and designed to provide both hot water for heat (separate loop in heater) and residential / light commericial use.

Have a friend here in DE who is using one and very happy with the results. In fact I am also considering one for an expansion project.

Polaris hot water heaters

I have no axe to grind since I don't know/use the products, but in a google search it appears from the number of folks griping that the units use an igniter instead of pilot light to save fuel. It appears that the igniters fail at a fairly high rate and leave one with no heat/hot water at most inopportune times. So I can only suggest PEW that you do some checking before installing one in your project. Results sure scared me off.
However, I am having a problem finding other units that do the same thing from any of the usual water heater manufacturers

Thanks for the info. My friend has been pleased and has had it for close to 10 years. But, no hot water can be a real bummer, will have to check and see if they have the problem corrected.

Paul