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HVAC Issues: Furnace and A/C compatability

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May 21, 2013, 05:42 PM
HVAC Issues: Furnace and A/C compatability
My A/C unit hasn't worked for several years. There was a slow Freon leak, which I was told by servicemen was just too hard to find so I ended up just topping it off every year, until one day that just didn't work any more.

Other than some parts for the A/C, the HVAC system is 40 years old, including the furnace. Although the furnace isn't efficient, it still runs.

When I met with an HVAC contractor to discuss replacement of the A/C components, I was told the entire system had to be replaced...furnace, ductwork, etc. I thought he was trying to scam me, as he then quoted about $8K for the system.

Question now though is whether or not this could be true? Ignoring the issue of the 40 year old furnace (which obviously raises the cost I'll pay), can I get a new air conditioner without having to change out the furnace, or are there some compatability issues to be addressed?

If I do have to get a new furnace, does the existing ductwork have to be replaced? (The furnace is a gas furnace).

Any other information you need to know to answer?

Thanks for any suggestions.

This message has been edited. Last edited by: GardenSprite,
May 21, 2013, 06:35 PM
You definitely need to get the new A/C and furnace as a matched set. Trying to match one to another that is that old is a waste of time (and money)

You may need to replace ductwork but this is much less likely. Some old ducted sytems (coal furnace, oil furnace) were set up with a central location that emits heat, with many return air vents scattered around the house - this is backwards for what works best in a modern system. Still, unless the ducts have physically deteriorated they should be able to be used. Then, it becomes an issue as to how efficient the ducts may be.

The bad news: $8K for a new system is not that much out of line. Actually, if they quoted that price for the new heat & A/C unit plus ductwork, it's quite reasonable.

The good news: Compared to a 40 year old system, a new, high efficiency system will not only be MUCH more comfortable, it will actually pay for itself in just a few years (like 3 to 5). That's how much lower your monthly utility bills will be. Your old unit was only about 60% efficient when it was brand new. After 40 years, it's likely operating at about a 35% efficiency rating. Compare to the new unit, which will be somewhere about 97% efficient. That directly translates to having your utility bills cost less than half what they are now.

One other thing to consider especially if your cash-flow is not great: Many utilities offer low interest loans for upgrading to high-efficiency units.

May 21, 2013, 07:01 PM
Jaybee, thanks for the answer, even if it wasn't what I was expected or had hoped for.

I'm not unaware that such an old furnace is a money sieve, but that's a lot of money to shell out at once.

I'm not sure what the first furnace was but it was centrally located as is the current furnace and has ductwork that spans out in various directions to each of the rooms.

So that I understand what's best for a modern unit, how would the ductwork be configured or reconfigured? It seems logical that it would beentrally located to lead each room. Guess I'm a little bit confused on this issue.

And how can it be determined whether the ductwork is efficient enough to stay or be replaced?

The $8k was for everything, including a new electronic air filter. Actually this was a few years ago; the issue arises every summer when the temperature soars and it's uncomfortable w/o AC. One of the primary reasons I haven't done anything is b/c I didn't plan to stay in this house and expected to be gone by now.

Thanks for the information.

This message has been edited. Last edited by: GardenSprite,
May 22, 2013, 01:58 PM
unless you had a gravity furnace, and they pretty much gave up on that stuff in the 50s, you will have a central duct trunk with branches to the rooms... if the installer back then was properly trained. our place is. almost all are close enough.

older (50s/60s) duct systems will also generally have dampers installed so the field workers can compensate for the lack of engineering in the system.

the use of computer plans is so ubiquitous now that anything a franchised dealer of HVAC is going to do is going to be inherently balanced as new work. the techs have good duct flow gauges that will allow them to fire up your existing system (even in fan only mode) and read the airflow at each supply register. from there, they can work backwards and determine if your ductwork is efficient enough, or whether they have to punch a few holes and pull new ducting in some areas.

where any extra cost is going to come in is in any ducting rework.

bonus, bonus! ==> we have passed May 12th, or whatever the cutoff was, and any new gas equipment installed has to by law be over 90% efficient. other fuels, there are some exceptions, but you can nudge 80 percent either way on oil. if I had your furnace efficiency as Jaybee estimated from the crud buildup inside of 30% in my Minnesota heating zone, I would cut my fuel usage 2/3, winter to winter comparison. that's $800 a year in my case.

the a/c probably rises from a 6 or 8 SEER to a 14 or 16 SEER efficiency, so you will see just under half the a/c cost saved per comparable season (the power to turn the fan stays pretty constant, so it's not a straight half-off savings.)

it's worth doing. our next replacement would go from oil to gas, so I also have a tank removal and a gas line install, so it will be equal cost for 5-8 years, and then savings from that point on.

if you move... the old HVAC at replacement point will cost you at least $5000 in your home sales price. the newest equipment might get you a grand or two extra in the bottom line. it's close enough to break-even that if you spend one more year there, the increased ability to sell quickly to somebody who has no more money for upgrades (meaning everybody -1) is also a plus.

( resale: you have to disclose in MN, at least, if you have buried fuel tanks. they could leak any time after 30 years, and that's a nasty remediation process, and costly. you are money and hassle ahead to pump out and remove the tank, the $1200-1500 is another $5000 ROI.)

inability to finance it is the only reason I could see for not doing the replacement.

This message has been edited. Last edited by: swschrad,

sig: if this is a new economy, how come they still want my old-fashioned money?
May 22, 2013, 07:04 PM
Swschrad, thanks for the information.

If I understand correctly, the ductwork would be tested before/at installation to determine what adjustments and/or new ductwork may or may not be needed? So a total cost estimate is dependent on these tests? I assume the ductflow issue would also be dependent on dust and gunk buildup in the ductwork?

Sorry to be so obtuse; my brain is a bit slow today.

I do remember those old gravity furnaces and the oil ones as well. We had a big tank outside the kitchen window for oil storage. And to take you back even farther, we had a coal fired furnace in the first house I lived in. Storing all that coal was really messy. I remember all the coal dust flying when the delivery truck poured the coal in the storage area in the basement.

I did some quick break-even calculations based solely on the savings. If that were the primary consideration it wouldn't be worth the cost.

But there are the other intangibles as well, including the desire to sell quickly and to dimish the moisture buildup from lack of workable A/C. Given that the adjacent land (and possibly my property) used to be swampy, the moisture issue is almost as important as the sale issue.

There's a lot of cheap housing competition in some areas of SE Michigan. So I need whatever edge I can get.

The financing will be in place shortly after Memorial Day, so I'll start getting estimates now.

Anything else you might want to suggest, in terms of good, best, better furnaces and A/C units? I do want an electronic air filter, or are those standard?

On the issue of buried tanks: I don't know if Michigan has such a disclosure requirement, but I have no indication that there are any buried tanks on my property.

When I worked in commercial real estate financing and development, environmental assessments were always done for acquisitions. You're right that remediation is messy and costly. It can also be and frequently was a deal killer. And brownfield cleanups can be even worse.

Thanks again to both of you for your help.

This message has been edited. Last edited by: GardenSprite,
May 22, 2013, 07:46 PM
duct insulation 40 years ago isn't what it is today. chances are that there are numerous leaks as well. I think that if you keep the ductwork you now have, you will have a nicely air conditioned / heated attic, though even if you have a system with a high E.E.R. its going to lose it to the attic
May 22, 2013, 09:41 PM
old duct work can be salvaged...
IF its not all rusted ou. the leaks can be stopped by using a duct sealnt we call "pookey"

it comes in gallon buckets at your plumbing/ac supply house
after painting the duct with pookie, it can be re-insulated

this may save you some bucks. i have noticed that as of lately the duct that is used in residential is far enferier to the old duct used
they use flex duct on everything, the old duct is REAL metal duct i would rather refurbish it than replace it with a lesser product
ask the ac guy to give you a price on refurbish the old as compaired to replACEing*****?v=vn7bkncf1_E
May 23, 2013, 09:07 AM
Nona and Frodo, thanks for the tips and advice. Seems like the ductwork is going to be a big issue.

I have some research to do on the issues you raised and probably will be back with more questions but just wanted to thank you for your time and replies.

(I also wanted to push down 5 spam posts right in a row.)

This message has been edited. Last edited by: GardenSprite,
May 23, 2013, 11:59 AM
latex duct sealer is availiable in some home centers as well, I found what amounts to 1+ quart pails at Menards. duct leaks in round ductwork are easily fixed with the aluminum duct tape. the C-channel stuff in rectangular ducts can be fixed with the lighter latex or the heavier-bodied material Frodo referred to. you could hold an airplane together with his stuff.

galvanized ductwork is basically a spec-80 material if you don't have it holding water. monkeys supervised by the apprentices' kids working on branches might twist and mangle some of the 90 elbows, as I found in my house when the basement ceiling came down. you just go and get a new 90 at the center, push it into the hole, reach in and bend the tabs over, take up the slack in the round duct joint to joint to slip it over the new ell, and straighten everything up, wipe off, and tape up.

oh, and ductwork... every time you work with it, you get cut. keep it to a minimum, get some good double-layer canvas gloves or some leather-bottomed gloves, and keep your eye protection on.

This message has been edited. Last edited by: swschrad,

sig: if this is a new economy, how come they still want my old-fashioned money?
May 23, 2013, 02:54 PM
the alumimum duct tape refered to is some good stuff
i use it.
but i have noticed that it will come off in the attic heat. is nothing good anymore. so put a screw thru it
then pookie over it.*****?v=vn7bkncf1_E
May 23, 2013, 03:13 PM
Swschrad and Frodo,

Thanks for the updates. I took a look at the ductwork in the basement. From the outside, it looks to be in decent condition, other than one register which is loose. As I recall, I remember accidentally damaging it when I opened it to let the a/c help remove the humidity from the basement.

I didn't see any rust, but I assume that's not an indication of what's inside?

Swschrad...did you take down the basement ceiling as part of your ongoing remodeling efforts, or was this some kind of accident?

I do have the heavy duty gloves, a present from my father who's worked with metal for years. Although they're clumsy, sometimes I use them to maintain the raspberry patch. Thanks for the warning.

Frodo, there's only one duct in the attic as far as I can tell. The house is a 1.5 story bungalow, with the cold air return ductwork behind the kneewall. Hot air vent ductwork must be in the floor.

At least that's not too much crawling around in cramped spaces to deal with.

I didn't get very far with my research this morning. Frodo's garden question tempted me away as I'd rather write about gardening.

Back with more questions, later.

Thanks again to all of you for sharing your experience and knowledge.
May 23, 2013, 03:25 PM
DeBasement ceiling... part of it fell as a result of a pipe corrosion issue. have written about this before, a dumbkopf putting in the plumbing rested the copper pipes on iron nails while installing it.

which is not unheard of as a crutch.

leaving them up as the pipe hangars is a guarantee that there will be electrolytic corrosion and the pipe will be eaten through. surprised and shocked that after 40 years, the other 10 nails didn't damage the pipe elsewhere. that's all fixed.

the big issue with DeBasement was that the foundation cretins used 12 inch block all around the house... until they got to the east side, driveway/garage. there they inexplicably switched to 8 inch thick block from the breezeway out to the corner, on the driveway side.

transitioning at ground level.

the hack fix they put in failed after maybe 30 years or so, and we had water running all along under the paving into the 4 inch gap and into the basement.

so we had to gut it to the blocks after finding and fixing the leak (4 months of monsoon rains started the day I corrected that issue, and not a drop of water, so I think it's OK) and redo it all. mold on all the drywall for starters.

I still have two blinds to hang Frown

sig: if this is a new economy, how come they still want my old-fashioned money?
May 23, 2013, 03:32 PM
Was this screw-up in the original construction? How did it ever pass inspection?

Sorry to learn that you've had such troubles. I was expecting an amusing story about redoing the basement to add a root cellar, ham radio office or something more positive.

What an ordeal.
May 23, 2013, 03:43 PM
original construction.

attic: good.

main floor: good.

basement: for some silly reason, after the framers were gone, it appears the apprentices' kids did the basement with 2-buck panelling and orange shag carpet. found 8 feet of Romex pushed up in the ceiling by a gen-2 added closet, with the dangling end open-spliced to 2 feet of wire to an outlet. all the basement floor pour had raw edges at the block walls, centipede entry, etc. a/c feed wire at 240 volts skinned from being pulled against the duct work, had to reinsulate that and staple some up. one 5-inch heating duct elbow was twisted almost out of the main run and damaged.

have found nothing like that mess anywhere else in the house.

everything in DeBasement is now redone to best practices at or over code, except I can't get the wife to agree to "splurge" on replacing the FPE entrance panel. I've already replaced 8 breakers in that thing. at least a master electrician and I went through it, the panel and busses are good.

The Joys of Home Ownership (tm)

sig: if this is a new economy, how come they still want my old-fashioned money?
May 23, 2013, 03:49 PM
Frodo: alum duct tape. yeah, our first furnace inspection in the place, during which we found the fuel oil going into the floor drain was from a failing pump, they checked for CO at the exhaust run. put aluminum tape over the duct. well, shuck my corn and toss hairs on my hat, what do you know, it won't stick on exhaust heat, either!

it does hold on everything else under normal use.

cloth "duct tape" doesn't stay on anything, unless you want to get it off.

new ducting is a couple gauges thinner than the old stuff, so it needs more hangars. better also have the Xs bent into it, or it will vibrate.

This message has been edited. Last edited by: swschrad,

sig: if this is a new economy, how come they still want my old-fashioned money?
May 25, 2013, 04:22 AM
Originally posted by swschrad:

cloth "duct tape" doesn't stay on anything, unless you want to get it off.

how true, how true !!! pookie it !

mech. co. i worked for, ALL new hires did nothing but pookie duct work the first week. terrible job
see if they could hang or not*****?v=vn7bkncf1_E
May 25, 2013, 10:30 AM
Quick question on the ductwork: assuming that mine can be upgraded with the methods discussed here, should this be done before, during or after installation of the new furance? I'm assuming that the ductwork would be tested for leaks, efficiency, etc. and determination made then whether it can stay or has to go? Then the patches can be added, or maybe even after installation of the furnace and A/C unit.

I need to get this all straight before I get estimates so I'm not led down the more expensive path.

May 25, 2013, 01:33 PM
it shoiuld all be done at the same time, should be done at the same time. but to be honest with you.residenial ac guys dont test the duct. its usually only commercial companies that test duct because its in division 1500 of the specs
if its in your contract. witness the test. dont take there word for it. they cap off all registers
and pressurise the system. 24 hr no leak test
put it in writing!!

in my humble opinon...get a trane unit. and get it a 1/2 or 1 ton bigger than they say. do not let them install duct board as your duct work. insist on metal duct work. insulated on the outside, NOT the inside. breds germs. and only let them use flex duct on the last 5' to hook up the register. flex causes friction, which causes turbalance, loss of air flow
some companies will run it all out of flex and make the plemium out of duct board. no no no!!!

if you can afford it. put in the contract to have them BALANCE the system when finished. that means: if your puts out 10000 cfm and you have 20 registers
you should have 500 cfm per register
and ..a louver on a register is NOT a balance damper
a louver is to direct the flow where you want it
a balance damper is a seperate peice of duct work
a balance hood, looks like an upside down trash can with a digital read out. its held over a register and measures the cfm output. do not let them try the old
feel that cold air? its balanced, trick

mix yourself up a spray bottle of soapy water, when they get done and put the freon in the system squirt the joints with the soapy water. wait 5 min. look at pipe if bubbly leak. better to find it now than latter
after the warranty

do not give them a dime till you are completly satisified. he can get mad all he wants. walk the whole system and look at details. then enjoy

This message has been edited. Last edited by: Frodo,*****?v=vn7bkncf1_E
May 25, 2013, 06:28 PM
Frodo, I understand what you're saying and you are absolutely right. BUT, I don't think you can get any A/C company to do what you say in a residential unit. They will just tell you to find another contractor, and of course none are interested. All they want to do is install a a/c unit and air handler and get out as quickly as possible
Here in Florida, you cant even get them to go in an attic during the summer unless you really pay a premium price, if at all.
I have been trying to get someone to check my ducts for leaks, and fix any that are found, I'm willing to pay whatever is necessary, but I can't even get them to return phone calls or e mail once I tell them what I want. Maybe something will change winter time.

This message has been edited. Last edited by: nona,
May 25, 2013, 11:12 PM
call a mecanaical contractor. not joes ac and heat
splain to them what you want. a commercial out fit is used to it. worth a shot.
i cant stand to see a house ducted in that BS fiber board and flex duct. its shoddy workmen ship
and i wont have it... in 20 years it will be leak city. you cant clean it. and mice love it*****?v=vn7bkncf1_E