GENERATOR BUYING

grsthegreat · Apr 27, 2011

jenkinsph said:
That is how I look at it too. I don't see the need to run a 20kw genset for power outages, I get by with alot less.

A typical set of heat strips in an electric furnace will need 19.8kw, a standard electric water heater (40 gallon) is 4.5kw, add a few smaller appliances and lights to this and you are past 30kw. Removing the two heating loads of 24.3kw can make a huge difference in what is needed. The amount of fuel needed could be conserved too, lessening the chance of running out in the middle of a long power outage.

i guess it all depends on the surge allowance of the generator. my 4.5 ton heat pump pulls 120 amps at startup...mind you only for a second or 2, but it does. Also depends on amount and size of the supplemental heat strips. ive wired up 20KW heat strips on units here in Idaho.

jenkinsph · Apr 27, 2011

Gary,

It does help if your power outage issues are not in the dead of winter. There is a big difference between using a heat pump with a high seer rating of 16 to 20 (expressed in btu's / watt) and resistive heat strips for emergency heat with 3.4 btu's/watt. When running the compressor the efficientcy is much higher. I suspect the breaker you are looking at is for the outside condenser unit, I would also look at the indoor unit and it's breaker.

I think practicing some judgement about power management would still be a good idea, staggering the cooking and baking, take showers after the cooking is done. All can make a big difference in the size of the genset needed.

grsthegreat · Apr 27, 2011

jenkinsph said:
Gary,

It does help if your power outage issues are not in the dead of winter. There is a big difference between using a heat pump with a high seer rating of 16 to 20 (expressed in btu's / watt) and resistive heat strips for emergency heat with 3.4 btu's/watt. When running the compressor the efficientcy is much higher. I suspect the breaker you are looking at is for the outside condenser unit, I would also look at the indoor unit and it's breaker.

I think practicing some judgement about power management would still be a good idea, staggering the cooking and baking, take showers after the cooking is done. All can make a big difference in the size of the genset needed.

most 5ton heat pumps i have installed have a 50-60 amp for outdoors and twin 50 amp to the indoor strips. some have a 100 amp to the indoor units and the indoor units have a set of 50 amp breakers installed on the unit. A 50 amp breaker would only have a rating of 12,000 watts continuous load....and thats if you allow it to run at 100%. most electricians rate the circuit size to 80% for safety.

jenkinsph · Apr 27, 2011

grsthegreat said:
i guess it all depends on the surge allowance of the generator. my 4.5 ton heat pump pulls 120 amps at startup...mind you only for a second or 2, but it does. Also depends on amount and size of the supplemental heat strips. ive wired up 20KW heat strips on units here in Idaho.

My mainstay in business is hvac contracting, so I am familiar with the consumption of the various types of systems. This past winter was very unusual for southern New Mexico in that we broke sixty year records for low temperatures, got down to -26 overnight and -4 for the high temperature for a few days. Needless to say lots of frozen pipes and people without enough heat. All the plumbing and heating contractors are still trying to catch up around here. Some areas lost gas pressure the demand was so high.

jenkinsph · Apr 27, 2011

grsthegreat said:
most 5ton heat pumps i have installed have a 50-60 amp for outdoors and twin 50 amp to the indoor strips. some have a 100 amp to the indoor units and the indoor units have a set of 50 amp breakers installed on the unit. A 50 amp breaker would only have a rating of 12,000 watts continuous load....and thats if you allow it to run at 100%. most electricians rate the circuit size to 80% for safety.

That has been my experience too.
If I were setting up an emergency generator I would want to take into consideration winter heat loads.

Last time I worked a govt job in Idaho for BLM was in the dead of winter, lot colder than in my locale most winters.

Gary Fowler · Apr 28, 2011

I have some more info. I had a generator installer come out and take a look. It seems that I have to take at least 10KW load from the heat strips off the generator load. Those are on separate breakers from the AC load so that would put to total load up around what everyone has been saying. I apologize for doubting the experts here. I dont have the luxury of walking out and looking at the breaker box since I am 7000 miles away at the moment. I dont know if he is removing all of the heat strips but it would be at least one circuit. I wouldnt think we would need more than that in capacity since a cold day in Ark is 20F where as in Idaho it might -40F.
Anyone like to volunteer some typical installation cost for installing a 20Kw genset and 200 amp automatic transfer switch. I would be setting the genset myself and getting the gas company to hooked up propane line . This would be electrical side of the installation only. I have a price from the one installer and would like some info on what others have had to pay.