90% efficent furnace requires new ducts?
My first post, your thoughts welcome.
My mother in S. Cal. recently had her gas furnace replaced with a 90% efficient unit. The county inspector told her that since it is a 90% unit vs and 80% unit, the ducting also needs to be inspected by another inspector in order to get a final at additional expense.
The installer said that while on the books for a while, the county just started inforcing this requirement. He also said her ducting (the flexible insulated variety) in the attic is too brittle and will need to be replaced for another $2500. I can understand the plastic around the fiberglass getting brittle but so what! Anyway the furnace is delivering heat to the house just fine with the existing ducting.
Can anyone shed some light on this and why it would be necessary for a 90% furnace and not an 80% unit.
I’m quite sure the manufacturer doesn’t account for the additional potentia expense in inspections and duct replacement in their payback equations for the additional efficiency.
Is it even worth getting a final since the furnace has is fine?
I’m confident the installer is not scamming her.
Thanks for your input.
Replies
Welcome to Breaktime mmches.
Someone from S. Cal can answer your specific queries best. (specific location would be helpful, click on your name and add the info to the profile)
Sounds like a bunch of BS to me. If the existing 80% furnace puts out 50,000 BTU/hr, installing a 90% 45,000 BTU/hr furnace would have the same heat transfer thru the ducts.
Why are you SURE the installer is not scamming?? Or for that matter, the inspector not in cahoots with installers??
Cases like this it sure is time to read all the local codes, educate yourself, and DIY.
This is a good place to start.
Edited 1/27/2008 9:28 am ET by junkhound
The inspections may be for the metal flue piping (ducting)... not the ducting that carries the conditioned air.
When an appliance is removed from the venting system, the existing vent is usually too large. Condensation (corrodes the aluminum liner in type B vent) and cold stacking (prevents flow of exhaust, resulting in spillage at something like a natural draft water heater) can be problems.
In an effort to keep prices low to get a job (because consumers shop for the low price, or use detailed proposals to DIY) little important details are forgotten.
A *properly sized* 90% furnace will only save 10% compared to a *properly sized* 80% efficient furnace. Additional flue venting expenses need to be factored in to the ROI equations. A variable speed drive DC blower motor will save energy dollars year round for minimal extra cost- even on an 80% efficient model. Installing a 90+% furnace without the outdoor air intake pipe (or an 80% without a nearby combustion air pipe from outdoors) is a waste of time.
Keep in mind that future energy costs will not necessarily rise in a nice even and predictable manner.
Get the most efficient properly sized furnace you can afford, and make sure it is installed properly.
Those flex ducts are another thing used to keep initial costs low, but replacing them is inevitable and not cheap... or even possible depending on where they are buried. The builder made his money, though.
question, why must you provide outside air intake with 90%, or waste of money?
One of the benefits of a 90% furnace is the ability to use outdoor air for combustion easily because the connection is right there on the furnace.
(Some brands, like Goodman, keep their costs down by making the entire top part of the cabinet the combustion chamber, and there are big knockouts that need to be sealed to prevent the combustion air from being pulled from the home [easier] than the pipe [harder]. Other brands have a sealed burner box that is quieter and doesn't have that problem with air leakage)
Why use heated indoor air for combustion?
You need something like 13 cubic feet of air to burn one cubic foot of gas (roughly 1000 btu's), and if you do not have combustion air piped in from outdoors, then that air comes into your home uncontrolled through openings like windows and electrical boxes... which you feel as drafts.
Someone willing to spend the money to upgrade to a 90+% furnace, yet only installs an exhaust pipe is wasting their money.
The same rules apply to plain old 80% efficient furnaces (gas,oil, propane- doesn't matter) and things like clothes dryers (electric or gas because they take indoor air and send it outside).
Drafty homes cause people to turn up the thermostat to become more comfortable.
Edited 1/27/2008 10:19 am ET by danski0224
< *properly sized* 90% furnace will only save 10% compared to a *properly sized* 80% efficient furnace>
No, no no!
a 90% furnace is 12.5% more efficient than an 80% furnace!
Not that it matters here! ;-)
Forrest - straining at gnats
>>a 90% furnace is 12.5% more efficient than an 80% furnace!Assuming those figures bear any relationship with reality.
May your whole life become a response to the truth that you've always been loved, you are loved and you always will be loved" Rob Bell, Nooma, "Bullhorn"
"We Live" http://www.youtube.com/watch?v=7kuBgh0VCqI&mode=related&search
And Annie Ross's "Twisted" http://www.youtube.com/watch?v=8lqivrCIRGo&mode=related&search=
Oh yeah, I forgot that math lesson.... :)
CA has lots of strange energy codes. Some more logical than others.
One is that the ductwork needs to be tested on new construction to see that it does not have leaks. And I am sure some kind of requirement for insulation on ducts in unconditioned space.
Possibly that have extended some of this to equipment changes also.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
When you instal a 90% efficient furnace are you eligable for a rebate? Sometimes these things are tied together. You get the rebate, they make sure it is right.
I'm all for acountability if it improves things long term.
It's hard to say whether:
A) You've run afoul of bureaucratic regulations regarding ductwork being brought up to code on a furnace replacement.
B) The issue really centers on the flue pipes, and there's been some misunderstanding.
C) The installer is trying to rip off your mother.
Ductwork needed for a 90+ furnace is no different than for an 80% furnace -- air is air. It is important that the ductwork be sound, with minimal leakage into unconditioned space, and that there not be any serious restrictions (too small ducts, flex duct that has kinked, etc). There may also be concerns with regard to fire protection.
In any event, $2500 sounds like a heck of a lot for replacing some ductwork in the attic, though of course it's hard to say without knowing more about the specific situation. But certainly your concern and further attention are merited -- too often older folks get ripped off by this sort of thing.
Mmches,
Looks to me like it's when any furnace or air conditioner is replaced, not just when it's a 90% effiecient unit being installed.
From the California Energy Commision Website:
Beginning October 1, 2005, Title 24 of the Building Energy Efficiency Standards requires that ducts be tested for leaks when a central air conditioner or furnace is installed or replaced. Ducts that leak 15 percent or more must be repaired.
There are a few exceptions depending on your specific situation and location.
I'm suprised your mother's HVAC contractor isn't aware of this seeing as how it was a permitted job.
Check this link out for more information.
http://www.energy.ca.gov/title24/changeout/2005-08-02_NEW_DUCT_REQUIREMENTS.PDF
Thanks to all for your input.Some good ideas and suggestions. Some more info for those interested.This particular furnace install is in Ventura County.
Again, it was the county inspector that said the ductwork would not need to be inspected if the new unit had been an 80% verses 90% unit. That is the part that seemed strange to me. It would have made more sense if he had been talking about the flue gases as one of you suggested, but apparently that is not the case.From references and personal contacts I'm standing behind the idea that the installer is honest and reputable and his comment was backed up by the county inspector and manufacturer that they only just recently started enforcing this provision. The suggestion that this maybe a requirement linked to energy rebate is a good one, although I suspect that it is "slightly" less promoted information i.e. Get $250 back on a more efficient unit, but it might cost you an extra $2000.I should have more info shortly. Thanks to all.
It may be that the inspector regards an 80% unit to be a direct replacement, but a 90% unit is an upgrade, and therefore requires that everything be brought up to code. If so, though, that's a lousy interpretation of the rules, since it's often cheaper to install a 90 than to maintain the chimney for an 80.Are you sure the inspector said the ductwork needs to be replaced, or is that what the installer said the inspector said?$2500 still sounds like an awful lot for redoing some flex ductwork.
If your view never changes you're following the wrong leader
Good thought on the replacement vs upgrade, see the link below.
The inspector didn't say the ductwork needs to be replaced, he just said it needs to be inspected, by some other department at additional expense, in order to get a final. The installer said that it wouldn't pass as it is too brittle....in the attic in S. Cal 24 yrs old, I can understand the plastic outside the fiberglass is probably shot. I just wonder if the internal material maybe just fine and even when replaced how does the installer actually test for leaks and if they can, why wouldn't they do that first so they actually know if they make a difference before and after. The link from panicmechanic was helpfulhttp://www.energy.ca.gov/title24/changeout/2005-08-02_NEW_DUCT_REQUIREMENTS.PDF
Mmches,
Here's another link that goes into much more detail about changing out HVAC equipment since 10-1-05.
If you scroll down to page 5 it states that there are no requirements for duct sealing during a furnace or A/C change out in climate zones 1, and 3-8.
I believe Ventura county is in zone 6.
Hope this helps.
Thanks, but your link did not come through.
Try this one:
http://www.energy.ca.gov/2005publications/CEC-400-2005-046/CEC-400-2005-046.PDF
PMThanks for the great link,I'll fill you in when I know moremmches
They won't test before, as they will only be looking to see if it passes whatever their standards are. Now you could request a test before, to see if they meet the standard, but you might have to pay twice, or pay some type of "re-inspection" fee if it doesn't pass the first time and you have to call for a re-inspection.And in this situation, that may make sense. You don't KNOW that they won't pass. Perhaps if you can get a hold of the the standards, you can do a test yourself. I have no idea what is involved, but I imagine you have to seal all the registers off and somehow attach a gizmo that measures input and leakage.
Mostly these things are calculated values and then the actuals are measured agianst them. Static duct pressure is used to extrapolate cfm in most commercial application. There are also actual devices to measure output cfm at each diffuser location, which is additive and compared to the rated output of the ahu, minus losses figured for transitions and friction.
We use to have a couple of guys and the equipment to do all that. Most of them retired and the equipment was lost or retired with them :)
The simplest way to test, after a visual inspection, is a smoke puffer or a simple incense stick. Course they only work for the duct works that you can get too. The ones in chases and wall just become a swag after you see what the others are doing.
Split outer sheath can lead to leakage.My in-laws had flexible duct whose outer sheath became brittle. I only found out because they complained that after a bigger furnace/AC unit was installed, one register had no air coming out. When I looked in the attic I found a section of flexible insulated plastic duct split open and blowing a substantial flow of conditioned air into the attic.
BruceT
bigger furnace/AC unit was installed
That by itself will "unseal" some duct work.
Don't get me started about oversizing a new unit cause the old one can't keep up any more.
Don't wanna rant, don't wanna rant, don't wanna......,
Out of curiosity now, how would someone go about testing the air leakage from a duct system? I'd love to be able to at least ball park that before rocking my current renovation (Pro [20%] DIY [80%] HVAC work, btw)
TIA."It depends on the situation..."
all i know is that i live in NYS and we don't have anywhere near the requirements that your state does. Don't people in cal. have common sense? It seems you have an awful lot of needless laws on the books.
Leaky ductwork has been found to cause cancer in labratory rats.
those damn laboratory rats.
But probably only in California rats. Thank goodness I'm not a rat.
Not sure. I had never heard of it in residential before this thread started.
I imagine it is a lot like a blower door test on a much smaller scale.
I don't know if this is the only way, but a Duct Blaster is one way.It is a door blower type of system.http://www.energyconservatory.com/products/products2.htm
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.