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Old 07-24-2010, 10:58 AM   #1
San Antonio Area
 
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Coverting to Heat Pump


Background: I currently have a Ruud Achiever 12,(R22) 4t 15 years old, with a 80% propane furnace. It works very well cooling my 2700 sf home in the San Antonio area. However I probably will need to replace the unit sometime in the near future. I am considering going with a heat pump, but keeping the propane furnace for backup heat. I have run the numbers and I would save about $450, a year in heating costs, maybe more if propane continues to rise as it has the last couple of years. Our current electrical rate is .097kwh, average propane costs, $2.65 gal. (1610 heating days a year) Question: Will I need to replace the indoor ecoil., it is rated at 48K.? What else should I be considering, different type of thermostat?, I currently have a Robertshaw digital programmable unit. Will the line set need to be replaced? I recently located my blower data sheet, the motor is 3/4 hp, 4 speed. Here is some of the stats. using .7 ESP, ( I used a higher ESP, because I believe few systems run at .5) High sp., 1910, Med. High Sp 1720, Med. Lo sp 1425. Will there be enough CFM to support a HP, 4 tons? Any help you can give would be appreciated. BTW, manual J say I have 43708 BTUH heat loss. Gary

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Old 07-24-2010, 11:51 AM   #2
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Coverting to Heat Pump


Replace the coil at the same time as changing to a HP for a matched set. You get the designed performance. Will need a HP thermostat and enough wires to run it. Line sets can stay if they are the correct size and flushed out.

Have the furnace heat exchanger tested for cracks. You have plenty of blower but at 15 years old it could have expensive problems in the very near future. Furnace inspection IMO is not a DIY project.

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Old 07-24-2010, 01:17 PM   #3
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Coverting to Heat Pump


Thanks Marty,
Where do I find the coil info. to make sure it is a matched set.? I understand there is web site ASHRAE?? I think, but cannot find any info on matching coils.

Gary
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Old 07-24-2010, 02:55 PM   #4
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Coverting to Heat Pump


http://www.ahridirectory.org/ahridir...ultSearch.aspx

Enter the brand and model number of the heat pump and the matching coils will show up

Last edited by Marty S.; 07-24-2010 at 02:58 PM.
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Old 07-24-2010, 04:16 PM   #5
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Coverting to Heat Pump


Yes, replace indoor coil at same time.
You'll need a dual fuel thermostat.
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Old 08-06-2010, 07:32 AM   #6
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Coverting to Heat Pump


One more question, will I need to change out the contol board inside the air handler to accommodate the dual fuel system? The current board is a United Tech 62-24084-01 HSI & remote sense (whatever that means). Furnace model ugph-10ebrjr., 100k btu.
Thanks
Gary
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Old 08-06-2010, 07:36 AM   #7
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Coverting to Heat Pump


No. The furnace control board has no bearing on the dual fuel set up. The dual fuel thermostat will take care of all switch over/outdoor temp lock outs.
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Old 08-06-2010, 07:41 AM   #8
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Thanks for your quick reply,

Can you recommend a thermostat, digital, does not have to be programmable and have all the bells and whistles, just something basic? Looking at Honeywell 3000 or 4000 pro, or maybe a White Rodgers, or Robertshaw.
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Old 08-06-2010, 07:52 AM   #9
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Coverting to Heat Pump


I prefer the Honeywell IAQ with outdoor sensor for dual fuel. It is a higher end thermostat. But it is better at controlling dual fuel then many other thermostat. The 300 and 4000 would require an additional dual fuel control. The IAQ doesn't.

The IAQ can be set as as a setback thermostat, or not to be setback. It gives you the ability to time in the gas heat, or only use gas heat when the outdoor temp is below X degrees. Or to set ti to bring in the gas heat if the indoor temp droops by 2 degrees, and the outdoor temp is between heat pump lock out and gas furnace lock out temp.

EG: Heat pump lock out set to 30, gas furnace lock out set to 40. Outdoor temp is 35, and the thermostat is set for 70, and the indoor temp drops to 68. It will switch over to the gas furnace.

This can happen on extremely windy days. or on a day when someone is bringing i a large amount of groceries.

The Honeywell TH 8320 can also do dual fuel, with its optional outdoor sensor. But isn't as adjustable on how it controls the dual fuel system.

Whoile the IAQ(YTH9421) thermostat is expensive. It is worth the money, because of how well it can control dual fuel.

I'm not real well versed o n White Rodger thermostats. But they have a few models that can also control dual fuel. Just not as well, as the IAQ.

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