# Thread: Backup electric strip heat question

1. Regular Guest
Join Date
Apr 2003
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43
Is there a set amount of KW back up electric strip heat per ton of Heat Pump? Is 15 KW strip heat enough for a 3 ton heat pump? (5 KW per ton)

2. Grumpy Old Man
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Apr 2003
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3. There's a possibilty that's right.... could be way off too.

4. Professional Member
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Apr 2006
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plenty...be sure and check available power at panel... 15k is a lot of amp draw w/heatpump

5. Do a load cal, and find out if thats enough to heat your house without the heat pump.

You might need 17 kw without the HP running.

6. Professional Member*
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Nov 2004
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SW FL
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## General Explantion of Electric Heat Strip Sizing

Originally posted by jrcase
Is there a set amount of KW back up electric strip heat per ton of Heat Pump? Is 15 KW strip heat enough for a 3 ton heat pump? (5 KW per ton)
Generally,
kW needed =
Total Heat Load - the reduced Heat Pump capacity at dsign temp ( 0'F to 35'F) depending on North or South U.S.

3 Ton ... ~36,000 BTUh Total
_______.. ~36,000 BTUh at 47'F
_______.. ~20,000 BTUh at 17'F
_______.. ~14,000 BTUh at 10'F ( ??)

For example, IF heating load for 2,000 S.F. residence is 50,000 BTUh at 10'F design temperature, a heat strip would need to provide 36,000 BTUh (50K -14K)
or 10kW ( 1 kw = 3,412 BTUh)

If your winter design temperature is 30'F (several Southern U.S. states), the heat pump would provide
~28,000 BTUh and residence may only need 37,000 BTUh
total heating capacity. Therefore, a 5 kW ( 17,000 BTU) heat strip would be MORE THAN sufficient to meet the 9,000 BTUh demand.

7. Size the strip to carry the full load, incase the OD unit goes out when its near design, if your design is below 30.

8. Regular Guest
Join Date
Apr 2003
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43
Thanks a million for all the replies. One more question. Do the heat strips only come in 5K increments? (5KW, 10KW, 15KW, ect.)Say I only need 7.5 KW, do I have to step up to 10KW or can I get 7.5KW?

9. Grumpy Old Man
Join Date
Apr 2003
Posts
6,383
Originally posted by jrcase
Say I only need 7.5 KW, do I have to step up to 10KW or can I get 7.5KW?
Check with your distributor for each manufactures available options:

5, 7.5 and 10 nominal KW models available with lug terminals

5, 7.5, 10, 15, 20, 25 and 30 nominal KW models available
with Circuit Breakers

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