Question
I have just recently installed my own irrigation system and every time it is on i have noticed that there is lack of hot water in the house. i have checked to see if the supply to the zone valve box is warm but it seems to be running cold water. i tied in the irrigation supply on the cold line coming down toward the hot water tank. I am wondering if maybe i should install a checkvalve downstream of the tee to the irrigation toward the the hot water heater. i have a feeling it draws hot water through the cold supply from the top of the tank

Answer
Hey Gus, more than likely what is happening, is that the sprinkler system is drawing a tremendous amount of water from the water feeding the water tank. In turn, the lack of pressure is due to the fact, that the sprinklers are using alot of water. It would be better to tie into the system somewhere either right before it enters the house, or soon after it enters the house. Even if the system is tied in at one of these points, a sprinkler  system will still drop your pressure in the house when it is running. Good luck and have a great day.