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Running hvac on generator

Posted by cindywhitall (My Page) on
Sun, Nov 4, 12 at 19:16

I'm getting a portable generator and was wondering about hooking it to my hvac. I have read many methods of hooking it up, transfer switch, interlock and considered installing an outlet near the breaker box and a plug on the furnace wire. I don't know if installing a plug would void any warranties, and I know some towns it is against code.

The plug would be my ideal solution as we didn't even lose power in the Sandy storm and I think the switches is $ I don't need to spend since I don't mind extension cords. Trying to keep costs down. Also, the smaller unit is more efficient on gas per Watts.

My question is mainly on the circuitry of the furnace. (2-stage carrier). Generators don't put out "clean" power from what I've read. How much of a risk is it to the hvac to hook a portable generator to it? I am content with the wood fireplace (which is not tons of heat, but better than none) and some electric blankets. I'm trying to get the smaller generator (3500W) so it can also be used for tailgating and stuff as we may never need it for power failure. I don't even want to consider hooking up the furnace if I could blow the electronics and my 10 yr warranty.

We'd run the fridge, flourescent lights, tv, modem/cable box. other things as needed, for which we could shut fridge off for a few hours. Fridge not really needed if it's really cold!

I might also post this in electrical forum.


Follow-Up Postings:

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RE: Running hvac on generator

You take a risk of damaging the electronics if you connect the furnace to a cheap portable generator. You may void your warranty if the HVAC tech figures out what you have done.

A generator with a built in inverter has a much cleaner output. These are more expensive but worth it if you are considering doing this.


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RE: Running hvac on generator

Mike, that's what I was afraid of. You live in NJ so you know we don't normally get bad outages, except nearer the coast. Are you in toms river? How did you make out?

I have lived in this house over 16 years with never an outage that lasted even 12 hours. My sister down near exit 38 on ac expressway lost hers for 3 days last year and this year.

Based on my experience a portable generator is all I will buy. I will just take my chances with space heat and elec blankets....if I had an old furnace I might risk the generator,but not my brand new one. Thanks for confirming my suspicion.It's too bad because my whole furnace would use less elec than a space heater!


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RE: Running hvac on generator

I live near Princeton. I had no power for 38 hours. I have friends in the next town who had no power for 4 days.

This is the first time I have ever seen a prolonged outage in NJ where the temperature was below 50 degrees. This was a very unusual experience. I would not worry about powering the furnace with a generator.


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RE: Running hvac on generator

That's good, 38 is tolerable, though probably the most I'd ever want to deal with. We had bought a 5000w unit that we didn't need, so we took it to my parents who DID need it, though only for a day. They bought it from me (it was new) when they realized it was a good idea after all. Since we didn't even lose power I decided to downgrade my replacement to the 3500.

They are going to look into a transfer switch. I will mention the possible problems with hvac, but their house is about 12-13 yrs old, old enough to risk hurting the furnace in a very cold time. They are in their 70's, but dad will not leave his house in a power failure. (paranoid of thieves even when there is NOT a failure!

Aside from the warranty, the unit could be repaired if there was a problem from the dirty power, couldn't it?

Hopefully this next storm doesn't cause anybody further damage. Thanks for your advice. You usually have good responses to posters on this site.


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RE: Running hvac on generator

Yes the furnace can be repaired.

I am also reading generators do not maintain a 60Hz frequency. The AC motors in blowers rely on the frequency being correct. If not they will spin too fast or too slow and cause further damage.


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RE: Running hvac on generator

My daughter in Bridgewater is STILL without power. She had a similar outage some years back (don't remember date).

We've also had prolonged outages (during IRENE, and others). here in Camden County (even with underground wiring).

V


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RE: Running hvac on generator

If you're buying a portable generator, spend the money and buy a Honda. There really is no substitute. Yes, you can spend the same money and have two crappy generators for the same amount you will spend on the Honda, but I can tell you that ours is 30 years old and still going strong. And yes, it will power the blower motor of a gas fired forced air system with no problems. That is VERY nice when we lose power from the ice storms! I only wish I could say that that is not a frequent occurrence here, but we get more ice than snow.


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RE: Running hvac on generator

V, I'm in Camden County also, Gloucester Twsp. Guess we were just lucky in my area. Heard Voorhees had some bad outages.

Until it happens to you it is really hard to spend the $. I must live in a really lucky area so I'm just going with having something less expensive and less quality than Honda that is hopefully better than nothing. I have read everywhere that Honda is the best, but never in my life have I ever said "boy I sure wish I had a generator", except for hubby going to the Eagles once a year.


My brother lives 6 miles away and my parents live 50. I'm gambling that at least one of them is reachable and has power if mine goes out for too long. 16+ years in this house with no prolonged outage. 5 years in a townhouse with no problems either. I'm gambling and spending the extra $ on a TV that I know I will use (but not with my cheap B&S generator!). I also know that if the big outage happens someday I will kick myself!

Would this work on a furnace (assuming it had a power cord)?
Power Bright 12 Volt DC to AC 900 Watt Power Inverter (home depot item # 202539660.) Would it be safer than a generator for power to a furnace? I know the car would have to be on....but it seems like it could be a useful gadget for short outages where you don't need to fire up the whole big generator, maybe to run the cable modem or charge something up. Or to take a laptop on a long car ride. The furnace would only have to run from time to time, not continously.


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RE: Running hvac on generator

As I said in another thread below,

"I did not lose power during Sandy, but it caused me to dust off my research into portable generators in part due to the problems many folks are having trying to buy gasoline to keep their generators running.

I do not have natural gas available, so I've decided I will buy a portable generator that uses propane as fuel. Propane will not likely be as difficult to buy as gasoline during a prolonged power outage.

In that you have natural gas, a simple valve and fitting can be added to your piping and you'll have a safe, inexpensive fuel source for your generator. Unless you lose gas, you'll be good for the duration of the outage.

These propane, or propane/NG, or Tri Fuel (propane or NG or gasoline) are all readily available."


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RE: Running hvac on generator

A 900w inverter is nowhere big enough to drive an HVAC motor.


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RE: Running hvac on generator

weedmeister said, "A 900w inverter is nowhere big enough to drive an HVAC motor."

Kohler, in sizing a whole house generator, suggests that for a furnace fan 750 Watts is a nominal running power requirement and 2000 Watts is a nominal Starting requirement.

They, of course, want you to get the actual data for your particular furnace.


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RE: Running hvac on generator

after seeing weed's post I looked around and it does seem to be around 800. Obviously they will all be different depending on size and model. I can find out for sure I bet if I go read the panel inside my furnace where it probably says...I have a 4-ton a/c so I guess my blower is on the bigger usage side.

The problem is accounting for starting watts which can be around 2000w. The blower will be turning on and off and we won't be able to control when that is happening, so we'd have to account for the whole starting wattage the entire time it's hooked up. That's how it seems to me anyway. That would really cut into what else could be run off a generator in the 3500-5500 which is what I was looking at for a portable.

For my purposes I will stick with space heaters and fireplace. I can more easily control the space heater even though it is high watt usage. I can simply shut off some other things until we get more comfortable. I'm not expecting total comfort, just to not be an icicle. Those of us with newer units also need to be more careful what we hook up to them.

Thanks for all the input. I hope others find it useful.


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RE: Running hvac on generator

For three days I ran two of my outdoor mini-split units*, a refrigerator and a chest freezer on a 6500 Watt genset. I only ran one of two indoor units on each of the mini-split systems. I kept an ear on it even though my calculations showed It should work. I never heard it bog down. It probably would running other connected indoor unit doubling the load. I was thinking of trying it, but about then the power came back on so I started to moth-ball the equipment and clean up around the property. I did have another 5000 Watt genset available.

* 18,000 BTU, RLA 10.1A, FLA LRA 15A and 22,000 BTU, RLA 11A, LRA 15A respectively.


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RE: Running hvac on generator

I thought about getting a generator some years back and decided I'd rather spend the money, if and when necessary, on motel rooms. It was the right decision for me, I'm many dollars ahead.

Everyone seems to get very annoyed at the few around who do have generators. I'm not sure why, but they seem to always get them going within 5 minutes of the power going down, even though it's often down for less than an hour. Maybe they welcome the chance to use them? And I know for some, they welcome the chance to p!ss people off. Just like the jokers who ride Harleys down the street late at night.


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RE: Running hvac on generator

Moving to a hotel is the ideal, except in the event that there are no hotel rooms available. Hotels filled up around here almost immediately. The closest hotel I could find was in eastern PA, which was just too long a commute to work.

Also, for those of us with pets, it can be difficult to not only find a hotel, but to find one that accepts dogs.

We were out for 7 days in October 2011. This year it was 8 days. That's why I'm on this forum reading generator threads.


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RE: Running hvac on generator

You also have consider those people who rely on electricity to run their sump pumps and heat their homes. For some people no electricity means a flooded basement and/or frozen pipes.


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RE: Running hvac on generator

In my case, I would readily leave town with the power off if not for my freezer. Giving up the freezer is not an option. I would significantly change my lifestyle for the worse.

With all the tall trees around my house, it is scary to be there with wind from storms. I've taken down two tall pines that could cut the house in half, but the neighbors still have one. I want to get automatic backup soon so I don't have to be there.


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RE: Running hvac on generator

" I've taken down two tall pines that could cut the house in half..."

And likely increased the wind loading on the other trees still remaining.

Nothing like a hole in the tree canopy to catch wind and pick off the trees at the edge of the hole one by one.


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RE: Running hvac on generator

Yea, I considered that facet. By taking down the two in my back yard, I reduced the likelihood of a tree hit on at least 7 significant buildings. Only two are mine. My neighbors are smiling more. I don't know why people are so short-sighted to plant these monsters on residential property.


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RE: Running hvac on generator

Mike, I'd commented that it was the right decision for me. I don't have a basement or sub-freezing temps to deal with, I understand everyone faces different circumstances.

Many people here have second homes in mountain ski areas several hours away. The ones I've been to (and rented) were all plumbed in such a way to allow for easy draining of the pipes - I guess I figured that was commonly done where sub-zero winter weather was a regular feature. Maybe not, but I'd think it would be easy enough to add to an existing house (and cheaper than buying a generator)


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RE: Running hvac on generator

When El Derecho came through Maryland in early July of this year I lost ~$600 in frozen and refrigerated goods. With hindsight, a couple of hundred invested in a generator would have been a pretty wise investment.


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