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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8164
Experience:  Furnace, A/C and heat pump specialist.
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Have 29 yr old Carrier refer system. Mercury thermostat

Customer Question

Have 29 yr old Carrier refer system. Mercury thermostat replaced w/Emerson blue easy set 1H/1C. Elec bill went from $93 to $155. Told therm is in dead space so paid $700 for Honerwell FocusPro TH6320R wireless. Elect bill went up to $202. Wall mount Emerso still measures temps due to batteries. Wireless and wall mount are only 1-2 degrees difference. System is turned off at night and not necessary until afternoon. Readings are 79 a 80 on thermostats. Early morning wireless is usually 78, wall mount 79. Never had these high electric bills with old thermostat, now more than doubled. System is in good condition and is service by same company in the fall and spring. What might be causing this situation? Thanks
JA: Just to clarify, do you think this is a larger HVAC problem, or something specific to the thermostat?
Customer: Something with thermostat. Highest bill with old therm was $110 several years ago. Therm was replaced last fall so Sept bill was $121, October bill was $76 which is very high for October the weather drastically cools so don't usually use ac very often during that month. This all started when thermostat was replaced. Was told thermostat is in a dead space, after 29 years in the house, never had these extreme elect bills until thermostat was replaced then was told since thermostat is in dead space and system is on the ground they weren't able to move the thermostat so pushed for a wireless which increased the bill even more,
JA: Do you plan on doing the work yourself?
Customer: What work?
JA: Anything else we should know to help you best?
Customer: Not at this point. Pls read that Emerson wall mount replaced carrier wall mont but the bill went way up so now paid $700 for the Honeywell wireless which now electric bill has more than doubled from when we had the old Carrier thermostat.
Submitted: 11 months ago.
Category: HVAC
Expert:  airheatman replied 11 months ago.

The issue is most likely nothing to do with thermostat.Probably coincidental.

The problem is your unit is old and therefore has lost efficiency. A 29 year old system could be compared to a 29 year old car.

Just as an engine, your compressor has valves that wear over the years.The unit is having to work twice as hard today to produce the capacity that it did 29 years ago.

Along with the age comes loss of actual capacity.In other words when new, it might produce a full 3 tons 36000 btus (3 ton example).After all these years capacity is loss due to wear and now produces only say 32,000 btus which requires it to work harder and run longer.

If you have further questions, please let me know.

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