I haven't had to use backup heat yet but I have determined I have 2  20kw backup heat strips with a 5 ton
geothermal heat pump, seems to be a overkill, just how much backup is needed to support a 1500 sq ft home ?

Are you sure you have two at 20 KW? That could require 4 pairs (8 total) 50 AMP breakers. Is that what you have?

I have 4 50amp circuit breakers, actually two each two section 50's. I was surprised by this, i have two seperate runs of wire in romex. seems to be a lot of backup power, is all this really necessary ?

Do you have one more circuit supplying power for the heat pump?

I am wondering if one of the two is for the heat pump and one for the strip heat.

Nope, it shouldn't be necessary, but I bet it can warm up your house pretty quick.

Just venting, but I hear people saying they have too much resistant heat, it doesn't matter, if you run 40kw for 30 minutes or 20kw for an hour it's still 20kwh total. More resistant heat won't use more power, it will just use it quickly and heat up the space more quickly, but in the end a kwh is a kwh or a BTU is a BTU.

So it shouldn’t hurt anything to have that much, just overkill and if an element (or three) ever burns out your still fine.

Thanks Brock, I suspected the same, however was really surprised when I started counting the 50's and checking the wiring. There
are two seperate wireing blocks attached to the back of the unit for wiring to the unit, a total of 4 blocks, one for the geo, one for the
water heater and two for the heat strips.
I have been told it was setup so that it would only come on if I selected it manually. thats a good thing, would hate to see that meter
spin with it runnning.

2 pairs of 50s would supply only 20 kW of backup, not 2 x 20.

20 Kw is just under 70,000 Btuh, perhaps enough to meet your home's entire heating load.

Yes, the meter will fly if 20kw all come on.

I just had a 4 ton WF Envision dual stage GSHP installed this month with a 10KW emergency strip.  The specs called for a 60A circuit for the heat pump and a separate 60A for the emergency strip.  Home size is 3100 sq ft of finished space but some is below grade.

The old outdoor air coil was on an existing 60A circuit so we reused that one and had another new one installed.

I would disagree when its used as supplemental heat
My thinking being
lets say for round number during aux call your heat pump is supplying 40kbtuh and you restance coil is 40kbtuh
lets also say your cop is 4 and 1 giving you a actual cop 2.5
system cycling quickly
now lets say your getting 40kbtuh from hp and 10 kbtuh from aux
giving you cop around 3.5
now your system is running much longer and overall more eff

I know if this situation comes up rarely and you want enough aux heat to keep up if the system fails but its my humble opinoin it does matter and should require some thought

Could be wrong though tend to be allot

Sounds like you have 2 double wide 50 amp breakers or 2 230vX50a circuits. One would support your 5 ton heat pump and the other a 10K aux. If you have a 3rd 50 amp (double wide breaker) then you might have a 20K aux which would likely have 4 sets of coils (5K ea.).
How many sf is your house again?
J

joe we have 1500 sq ft home and indeed there are two double wide 50 amp breakers, curious though with the terminations on the back of the geo being marked strip heat and there are two seperate blocks. I will take a picture tommorow and post. there is a seperate block marked geo, I guess that along with the packing slip that showed two 20kw heater coils led me to think there were two
installed. but as mentioned earlier one 20kw heat strip should provide enough btu for our house.

How long has your installer been in geo? 20K is big as is 5 ton, I don't think he has much faith in his product (unless i'm missing something).
J

geo fan,

You're right, could be wrong!

True is that with a smaller aux you get a higher system CoP. But in your calcs, for the first example total btuh out / total btuh in is 80 Kbtuh / 50 kbuh = 1.6 overall CoP. In your second example, system CoP is 50 kbtuh / 20 kbtuh = 2.5.

Regards, Masoud

I like round numbers for examples
(shhh Im realy bad at math)

Wow 20 KW backup heat! If were comparing Backup KW's, I only have 5 KWs, I feeling a little self consious right about now.... Actually I have Zero since the AUX heat is disabled currently. My goal was to be able to heat the house enough to keep the pipes from freezing in case the water pump quit. This way I would have something until the water pump was fixed. i could use space heaters for room I wanted additional heating in.  

  

Do you have KW envy?

Wow.. 5 tons for 1500 sqft... did you guys run manual j? Is there a large hole in the wall?

I wonder too. I have less than 2000 SF and our geo installed 3 ton

1500 SF home in Fairbanks, AK?

True true and true.  I wasn't taking in to consideration that a larger resistance bank would eat quicker in to the COP if it came on automatically.  I was thinking straight KWH.