A/C Electrical in a old home

[Clovis]

I hope someone can help answering a question to which I have been given different answers to by licensed electricians.

I live in Texas. My house has old electrical installation from the 50s which include a fuse main panel and a smaller breaker sub-panel. None of the electrical system has ground - the neutral is bonded to the plumbing. The a/c was replaced in the early 90s and now needs to be replaced again (both compressor and furnace). The conduit going to the 3 ton unit has two cables in it (240 - both hot) and although there is a ground cable between the disconnect and the compressor, obviously it isn't connected to anything on the disconnect. The a/c is connected to the sub-panel on 2 x 40 amp breakers. My a/c guy told me that I would need to have some electrical work done before replacing my units.

When faced with HVAC replacement in houses that have a grandfathered no-ground electrical system, what kind of electrical work generally has to be done in order for it to be safe? One electrician told me I need the main panel replaced, ground installation, rewire of several rooms in the house, etc... but that would mean doing a considerable amount of rewiring in order to meet code and would cost more than the a/c replacement! I know that this kind of work can be dependent on local code (and/or inspector), but even then I have gotten conflicting opinions from at least three home inspectors as to what is acceptable.

Any opinions - or descriptions of what you have seen as acceptable in a case like this - would be welcome.

Thanks,

C

[hvacvegas]

Ground rod for the A/C.

Rest of the house is up to you.

[motoguy128]

Just for safety, is worth it to replace the fused disconnect and sub panel with a modern panel, with proper ground rod. Then you can slowly start up grading other circuits inge future and do this like put major appliances on dedicated circuits. I did this in my home. It wasn't cheap, but I had 2 sub to remove and put in a commercial grade 40 space panel since it's a larger house.... and isolated circuits to the furnace, refrigerator, microwave, dishwasher, and entertainment system.


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[oldblue]

If all new panel is out of the question due to cost. I'd go ahead and run two ground rods and bond them to the fuse panel. Then run a new circuit to the A/C that way you wont be wasting money on the ground rod just for the A/C. You'll have a grounding system for the new electric panel ready to go. If cost is a major issue ground rod just for a/c will work but could have some added resistance to ground over a properly bonded panel.

I'd also talk with a local electrical inspector not a home inspector to see what he would approve.

[Clovis]

Thanks for your replies, really appreciated.

After some further digging, it seems that the norm around here would be a new panel, ground and new wiring for a/c, plus GFCI to kitchen, bathroom and garage with new wiring to those.

However, there is yet another "upgrade" that will need to be done. There are no return ducts to the furnace - the grilles around the house are open to the crawl space underneath (this is pier-and-beam) and the blower intake is open to the crawl space as well. From what I have read, return ducts should be installed while we are at it as it will save considerable cooling costs. At least a complete rewiring doesn't seem to be mandatory. Will be getting bids next week for electrical and a/c, including the duct work.

I read there are some new flexible ducts that can be installed much more easily than the usual (metal?) ones. One of the a/c guys I talked to about the return ducts recommends against using those in the crawl space as he says critters tend to chew on it. Has that been your experience?

Any suggestions as far as SEER is concerned? The old unit is a 3 ton, house is just over 1600 sq. feet. No tree shading, old insulation in the attic (windows are double-pane). Even when the old unit was working right, it would run almost continuously when the outside temp got above 100 or so, but I think if I have return ducts installed it will work much more efficiently. I guess with SEER rating, what you pay is what you get, right?

Thanks again,

C

[vstech]

no returns in crawl space? Critters chew on them? but not the supplies? what is this guy recommending? there are a LOT of homes with returns in the crawlspace... (yours is the first I've heard of that has an open return in the crawl...)

as for the electrical, since the a/c does not require a neutral, putting a ground rod near the equipment, and bonding the disconnect to that would be a step in the right direction, running a solid #4 cable from that to the main panel ground rod, and into the main panel is better still. Best of course, is total rewiring of the entire house.

[wahoo]

Ideally you should use metal duct or pipes to connect this return air. You can't use the dirt crawlspace as a return for numerous reasons, the least of which is efficiency. I'd simply add a ground rod to the AC unit. If you use flex, then you'll need to make sure this crawl is not open to rodents or critters as they'll chew thru the pipe. If possible, I'd use metal duct.

[Clovis]

no returns in crawl space? Critters chew on them? but not the supplies? what is this guy recommending? there are a LOT of homes with returns in the crawlspace... (yours is the first I've heard of that has an open return in the crawl...)

as for the electrical, since the a/c does not require a neutral, putting a ground rod near the equipment, and bonding the disconnect to that would be a step in the right direction, running a solid #4 cable from that to the main panel ground rod, and into the main panel is better still. Best of course, is total rewiring of the entire house.

This guy recommended a metal return to a floor grille somewhere in the house. Problem is, that could cause pressure imbalances in other rooms, from what I have read. There is at least one other large thread on this board about open returns to crawl spaces. Several people here said it isn't unusual for houses of this era (before we knew about radon, etc...)

Each room has a return air grille (open to the crawl space) except the bathroom and den, but the den doesn't have a door and is next to the living room, which has several grilles. Seems to me the best solution would be to have sealed ducts connecting those grilles back to the furnace, after doing the proper calculations. The crawl space is well sealed, never had critter problems down there - so will ask for bids on doing returns from all the rooms in both flexible and metal. Wish I could do some of this duct work myself but I had a bad injury to my arm and cannot even handle a screwdriver very well...

Two companies wants to re-evaluate the entire a/c system, including the attic ducts. Of course, that would be the "proper" way to do everything right, but I am sure the cost will be quite astronomical.

On the electrical, I think I am set on redoing the master panel/garage/bathrooms/kitchen for now - that will already cost a ton but better safe than sorry on the electrical. Some of the old wires look good, but some are cracking when handled. The electrician will do a full inspection on the wiring in the attic next week. If we have to replace them all - plus ducts, a/c, etc... - it will be time for a H.I. loan.