Potential rewiring for heat pump

dag63November 5, 2010

I am looking into replacing an old heating/AC unit (electric, but not heat pump) with a new 3 ton heat pump. The current unit has 60 amps dedicated to it and there is no empty space on the panel. My understanding is that with heat pumps, the outside condenser and the inside air handler need more than 60 amps combined to run when it is sufficiently cold outside (because of the heat strips in the air handler).

The outside unit is on the opposite side of the house from the panel, with the air handler in the middle. The unit is on the first floor of a two-story house. My first estimate for the upgrade was $2500+, which includes adding a subpanel for at least 2 - 30 amp breakers and running new lines from the box to the air handler and then to the outside unit.

First, is my understanding/explanation correct? Second, if so, is this all necessary or are there other options? Third, if it's necessary does the bid sound reasonable?

Thanks for any advice on this.

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smithy123

i personally would install a 100a breaker in the main panel and install a squareD qo 100a 6 space panel next to the inside unit. the $2500 seems rediculous, i gave my neighbor 2,000 to replace her service.

    Bookmark   November 5, 2010 at 3:36PM
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brickeyee

Depending in the age of the panel you may be able to use reduced size breakers to gain more circuits in the same panel space.

Four full size breakers are replaced with two half size providing four circuits, and the two slots can then be used for a 240 V two pole.

    Bookmark   November 5, 2010 at 4:29PM
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smithy123

i beleive a line of sight disconnect as well as a gfi within 25' (probably gfi because plumbers tend to pull grounds in my area) is required. i also reccomend square d, but as long as you do not have federal pacific, zinsco/sylvania gte you are ok.

    Bookmark   November 5, 2010 at 4:50PM
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dag63

Thanks smithy and brickeyee.

I think the panel issue is the least of the problems (or at least less costly). The biggest cost issue is getting the additional power from the panel to the heat pump units without any crawl space to work with. After checking back with the electrician on some of the specs, his bid is down to $1800. I have at least one or two other bids to get.

    Bookmark   November 5, 2010 at 5:43PM
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dag63

I guess the bottomline question is: can you run a 3 ton heat pump on one 60 amp breaker? If so, how does it work? What is the max heat strips (10kw?)?

    Bookmark   November 5, 2010 at 6:25PM
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smithy123

i personally would install a 100a breaker in the main panel and install a squareD qo 100a 6 space panel next to the inside unit. the $2500 seems rediculous, i gave my neighbor 2,000 to replace her service.

    Bookmark   November 5, 2010 at 7:14PM
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pharkus

I personally would install a shotgun in smithy's monitor, powered by an ITE Pushmatic breaker.

Repeat posts seem annoying. I gave my elementary-school spelling teacher nothing to teach me how to spell "ridiculous"

On a more serious note...

Anybody seen these evil contraptions? The whole design has a "there's no way this thing is legal" feel to it, and yet, somehow, they are... if Fisher-Price made electrical equipment . . .

Anyway, if they weren't such cheeeeeeeeseball inventions, one of these would seem a reasonable proposal.

    Bookmark   November 5, 2010 at 7:37PM
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Ron Natalie

Are you talking about two pole tandems? While the reach around handle tie looks like a kludge, there's nothing electrically or mechanically wrong with it.

    Bookmark   November 5, 2010 at 11:36PM
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weedmeister

Remember that the HP and the blower are two different things. The HP (outside condensor) may be 40 or 50a. The inside blower may be 50 or 60a depending on the size of the heat strips (without heat strips it will be much less).

Have you thought about running the line to the outside unit from the panel around the outside of the house? That's just one circuit, not two.

    Bookmark   November 6, 2010 at 12:43AM
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pharkus

Yes, I'm talking about 2-pole tandems.

I've only ever seen two. Both of them, I was able to turn off one pole without the other pole turning off. That "reach around tie" doesn't work very well.

Irrelevant I suppose, but it just makes it feel cheesy.

I saw some old double breakers with the handles in line with each other, like, end-to-end, rather than side-by-side... They looked very QO, but I wasn't tearing apart the painted-over-multiple-times panel in the middle of a concert just to see what company made it. :) Eitherhow, I would think this would be a MUCH better design on which to base a 2-pole double.

    Bookmark   November 6, 2010 at 3:47AM
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smithy123

sorry about the double post, it was an accident. I have seen a QO quad in a wiring book from back in the 2000's, like 2001 or around there. i think it was wiring simplified.

    Bookmark   November 6, 2010 at 8:29AM
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Ron Natalie

QO makes the ones similar to the ones you mention. I sort of like the GE skinnies. They make two pole skinnies, they straddle the bottom of one position and the top of the next.

--

But getting back to the subject. Did your read your manual? 60A would, based on off the cuff research, be fine for the 3 ton pump itself. You may need another breaker for the resistance "emergency" heat. The air handler typically doesn't draw much at all but usually is run on a second circuit as the blower and control logic is sometimes only 120V. You will need a maintenance disconnect but there's no requirement for GFCI anywhere. You will need to make sure the breakers for the pump are HACR rated, but most big dual poles are these days anyhow.

$2500 sounds egregious to put in a subpanel. I paid less than that to replace my entire main panel with a bigger oen.

    Bookmark   November 6, 2010 at 8:36AM
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smithy123

my friend's nec reference book said one was needed, but they may just mean the outside.

    Bookmark   November 6, 2010 at 11:43AM
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brickeyee

The outside disconnect does not need any over-current device, just a disconnect.

They are commonly placed very cloe to the unit and used also to change from NM (or other in house wiring methods) to an outdoor wiring method to feed the condenser.

You can purchase a 'whip' of outdoor flex, conductors, and cable connectors to match most residential units at any supply house.

    Bookmark   November 6, 2010 at 1:10PM
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Ron Natalie

Inside, outside, upstairs, downstairs, it doesn't matter. A heat pump does not require nor is it advisable to put it on a GFCI.

You have to read the words in the code, not just look at the pictures in your buddy's coloring book.

    Bookmark   November 6, 2010 at 4:12PM
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smithy123

no, i meant a gfi protected receptacle within 25' of hvac equipment.

    Bookmark   November 6, 2010 at 5:54PM
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Ron Natalie

No such requirement. If you're not going to actually read or at least learn about the code, why bother posting?

    Bookmark   November 7, 2010 at 2:45PM
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smithy123

i do not have the nec, but i want it.

    Bookmark   November 7, 2010 at 4:30PM
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hexus

"i do not have the nec, but i want it."

I want to have a Ferrari, but I don't go around posting like I know everything about them.

You're an embarrassment to the electrical trade in most of your responses.

    Bookmark   November 7, 2010 at 5:01PM
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pharkus

Again, smithy, send me an email via the link on the profile page . . .

    Bookmark   November 7, 2010 at 6:39PM
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smithy123

im learning.

    Bookmark   November 7, 2010 at 7:54PM
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pharkus

smithy, I have something you want, but it needs to be done privately, NOT here in the forum.

YOU are not able to be reached privately, so you need to contact me.

    Bookmark   November 7, 2010 at 9:13PM
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Ron Natalie

The public library has NEC's around here. I've got some older versions of the handbook (essentially the code with some extra description and annotations) I can probably part with. I've switched to using the online NECPLUS a while back because I can get multiple versions of the code conveniently without lugging around the big code books (the two states I'm working in are NOT on the same version of the code (and I've been studying the 2011 one in advance of that being adopted).

I believe there's a separate nfpa site that gives you and older version of the code (better than nothing) with a really ugly interface to read it (different than the much nicer necplus pay service).

    Bookmark   November 8, 2010 at 8:00AM
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smithy123

alright, pharkus, i emailed you.

    Bookmark   November 8, 2010 at 4:01PM
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