We got a call from a local home builder in Louisville, KY last week because one of their clients was complaining that their electric bill had spiked in the last 2-3 months. The house was just over a year old and was insulated and air-sealed very well when it was built (we did the HERS Rating on it), and the homeowners had not had any high utility bills until recently, so we assumed something had to have changed recently to cause this.
High electric bills in the summertime are most often the result of inefficient A/C systems, so we started off by taking a look at the HVAC system to see if there was a problem with airflow. Poor airflow due to clogged filters, A-coils, or other obstructions in the duct system can decrease the overall efficiency of the system and increase utility costs as a result.
The A-coil was clean, along with the blower wheel, so we checked airflow through some of the vents throughout the house just to make sure airflow wasn't the issue. The airflow was adequate, although we did find that the system needed more return-air openings added to help reduce the static pressure on the return-side of the duct system. Since there was no return-air vent located in the unfinished basement, this was the easiest and most logical place to add a return air vent, so this was our first recommendation.
While we were inspecting the A-coil in the basement, the electric water heater was right next to us and we noticed that it was ejecting hot water out through the temperature & pressure (T&P) relief valve at the top of the unit.
Temperature and pressure (T&P) relief valves used on residential water heaters are typically designed and manufactured to relieve pressure at 150 psig and on temperature at 210 degrees F. These valves protect the water heater from damage caused by excessive pressure and temperature by discharging the hot water within.
In normal operation of the water heater and T&P valve, no water should be discharged from the valve. A T&P valve that discharges is a sign that something is wrong inside the system and by discharging, the T&P valve is meeting its designed safety purpose. The causes of discharge can be thermal expansion, excess system pressure, low temperature relief, too high a setting on the water heater, or something in the water heater causing excess temperatures in the heater.
We asked the homeowner if they were running hot water anywhere while we were there and they said no. This was a clear indication to us that there was an issue with the water heater that needed to be investigated further by the plumber who installed it. If this water heater had been overheating consistently for the last couple months, this most certainly could be the main cause for the homeowner's spike in electric consumption.
Our final recommendation to the builder was to have the water heater fixed or replaced as needed, add more return-air openings in the basement, and check the refrigerant charge in the A/C system to make sure that wasn't also a contributing factor to the high bill complaint.