Water Heaters - Apollo Model 5010

I'm new to this network and am looking for information on the Apollo model 5010 water heaters. It is my understanding that the water is recirculated to help heat the home. There seems to be a second pair of water pipes coming out of the side of the unit(s).

The upstairs unit went out, do I have to replace with a Apollo unit? What other things shoud I consider? I don't want to have to replace the upstairs heating unit as well.

Apollo water heaters are used for both Domestic hot water, and for hot water home heat. They have side taps or openings to allow the higher than normal Btu hot water to be moved to a coil in the attic normally. Air is blown across the coil and is used to heat the home. Apollo water heaters require a Mixing valve to temper the Domestic hot water to a Safe temperature for home owner use. It also requires a Loop kit for use with the attic coil unit where air is blown across the coils producing the heat for the home.
The coil unit in the attic does not have to be replaced with an Apollo coil, it can be any manufacturer that uses water for the coils, to produce heat. Apollo water heaters come with Btus (British Thermal Unit) ranging from 40,000 to 75,000 btu's, depending on the size gallons of the water tank.

Sincerely,
W Richardson/ Jimmy's Plumbing Supply