Stacked HP and NH4 furnace.
Did an unconventional installation for reduction of total energy bills at son’s house a few years ago. Stacked 4 T HP indoor unit on top existing gas furnace, 2 separate and independent thermostats and power circuits, side by side 120/240 Vac power switches for selection on wall by units in garage. Used 2 separate switches as son is smart enough to have either one or the other (20 F is the gas furnace manual switching point) engaged but not both. Totally separate systems, separate 24 Vac transformers, tstats, circut breakers, etc; but same duct system. Downflow setup, gas down from HP. (PS – I’ll not get into scenarios where I told son to let BOTH operate)
Son is selling home: Query?: Should I install a 3 pole DT switch for the AH to gas furnace switchover in place of the (labeled as to operation) 2 manual switches now? What codes cover this if any? No concept of how dumb homeowners can be, except for bus segment horror stories on BT<G>
Replies
What stage of selling is he in and what kind of market?
Something "strange" like that (not that I would not do the same thing) might through off a sale.
The cleanest way to solve this would be to get one of the high end thermostats, such as the Honeywell Vision pro's that have optional outside sensors and can be programs to handle this.
But those are a lot more expensive than a SPDT switch.
Thanks for the reply Bill, I respect your opinion in these matters above all others.
Seattle market, very HOT. Son 'upgrading' to similar house on more acreage. Asking price for their present house is 2X what they paid 4 years ago, house they have a contingent offer on sold for less than 1/2 5 years ago of what they offered. 7-800K region.
The "strange" part is what caused me to remove the homebuilt logic/uP circuits (did not mentin in orig post) and relays and outdoor sensor that switched systems automatically (using the same Honeywell 7 day programable 'furnace only' tstat) and putting in the 2 simple switches (did not have a 3PDT switch on hand). System probably would have been unserviceable by a nominal technician even with the schematics (was it you who once used the 'inspector gadget" phrase?) due to relative complexity when fully automatic - needed weather condition and fuel price inputs(at machine language level) yearly or whenever price structure changed.
Talked to the son's realtor about it today and she thought is was straightforward with just the 2 switches and would be a selling point having dual fuel capability as nat gas is going to break $1 therm here and climate and elec rates are ideal for HP (4700 sq ft house). Payback at 92 cents/therm for adding the stacked HP/AC (not counting my labor) was under a year.
I'm glad I'll be dead whenever house I'm in now is sold, as there are custom circuit interties between HP, fireplace, FP circulating water, HW heater, probably parallel GSPH next year, custom whole house lighting control (RR relays, non-standard switches), 3 ring-loop multibreaker circuits to 5 outbuildings, 12 simplex pushbutton door locks with combo reset keys removed, etc. etc.