Heat Pumps

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LocoKen

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General question here. The sizes of heat pumps are characterized by the tonnage, correct? And if so, what amperage rating would you use for a 4 ton HP?

How low/high do the tonnage ratings go and how do you determine the circuit conductor size if you don't know how big the HP will be if only the furnace is installed? Thanks! :)
 
The heat pump info is on the unit. You must use the nameplate ratings.

I usually call the heating contractor and find out the specs from them. I want to know max fuse or CB and min circuit ampacity.
 
Sorry, I forgot to add that the HP is not on site yet, but the Heating/AC guy left a note saying the HP is 4 ton.
 
LocoKen said:
Sorry, I forgot to add that the HP is not on site yet, but the Heating/AC guy left a note saying the HP is 4 ton.
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Ask that, from now on, he leaves a note specifying the minimum circuit ampacity and maximum over-current protection (and if it only says "fuse").
 
Heat

Heat

:D
LocoKen said:
General question here. The sizes of heat pumps are characterized by the tonnage, correct? And if so, what amperage rating would you use for a 4 ton HP?

How low/high do the tonnage ratings go and how do you determine the circuit conductor size if you don't know how big the HP will be if only the furnace is installed? Thanks! :)
Click to expand...


If you don't have all the spec's but you know the tonage, I use this rule of thumb for calc's. 1 ton = 12000 BTU

1 watt= 3.412 BTU


ex. 4 tons x 12000 BTU = 48000 BTU


48000 div by 3.412 = 14068 watts

14068 div by 240v = 58.6 amps

Its not a percise science but it will get you into the ball park.
 
Number 1 rule don't ever believe what the HVAC guy tells you.
I remember the HVAC guy given us spec and then when the unit came it was not the same.
If you can Wait till the unit is there is my best advice.
 
We don't run conductors until we get the info in writing.

If the HVAC company does not provide it the job waits.


Number 1 rule don't ever believe what the HVAC guy tells you.
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LOL, that is why we ask for it in writing. :)

One time I got the info in writting...480, 3 phase 30 amps.

The unit showed up as 208 3 phase 60 amps.

We got a nice extra to redo what we had already done and the HVAC company had to pick up the bill.:D
 
iwire said:
LOL, that is why we ask for it in writing. :)

One time I got the info in writting...480, 3 phase 30 amps.

The unit showed up as 208 3 phase 60 amps.

We got a nice extra to redo what we had already done and the HVAC company had to pick up the bill.:D
Click to expand...

AH!!!! Don't ya just love it when that happens.
The best one is when the unit come in and they said sorry we could not get the one spec.
 
fc said:
The best one is when the unit come in and they said sorry we could not get the one spec.
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That was basically the answer, they had decided to ship the right unit to another job and then could not get another in time.

They tried to blame the GC for this......it did not work.:D
 
So from what you are saying, the heat pump and disconnect would be rated 60a. which probably would make the start-up current around 50+ amps but the heat pump would probably run at a lower amperage, no?
 
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