Heating Duct Problem

[Nords]

If you go sheet metal duct instead, you will have to buy a lot of fittings, do a lot of cutting, sheet-metal screwing, taping, etc. Then, you will have to insulate the outside of the metal duct, with care to make the outer vapor barrier continuous.

One duct company said that code requires that those be sheet metal and not flex duct.
I considered replacing it, but we simply do not use the furnace. I run it 10 minutes per month so that it won't feel neglected.

Sounds like you're stuck with either not using the furnace (and ignoring the mice noises/damage) or doing the right thing with metal ducting.

In the perhaps unlikely event that you sold the place, the inspector would point out that the crawl-space ducts didn't conform to code-- and you'd end up replacing them in a hurry or giving the buyer a retail-price discount. Maybe this is an opportunity to leisurely replace the flex ducts with metal, on your schedule and whenever you feel like working on it, and especially if you can get a good deal on sales or Craigslist "contractor extras". Replacing existing ductwork seems to be well within the capability of a homeowner with your skills & available time, although this time of year might be sucky weather to do it.

Besides a metal duct tastes yucky to field mice and rats.

Speaking of taste and mice-- your refrigerator water line and dishwasher supply lines are made of metal... right?

 

[TromboneAl]

Yes, good advice, Nords, and I've gone through the same thought process. Here are the counter-arguments:

First, we've gone for ten years without having this problem. So it's not definite that I'll just have to do this again in a year or so.

Second, I didn't find any evidence that the mice actually chewed holes in the ducts. I'll be able to check more definitively when they pressurize the system during cleaning, but my current hypothesis is that the mice come into the garage, then get into the ducts via the furnace. I trapped the two mice in the garage next to the furnace. If that hypothesis is correct, metal ducts won't solve anything. Also, increases in efficiency aren't worth it because we don't use the furnace.

Third, I could put in the metal ducting myself, and I'd enjoy the problem solving and learning experience, but it's just too damned cramped down there. Here's a picture:



That's why my plan is to clean the ducts, mouse-proof the house more, and watch and trap.

 

[samclem]

If I were going to keep flex duct down there, I'd be really tempted to buy some replacement flex duct (less than $100) and hire a handyman-type to install it. It would be less expensive than cleaning, the "problem duct" would be cleaner, and the job would be a lot less expensive (maybe an hour of his time = $50). If I were going to invest $500, I might consider paying that same guy to spread 4 mil plastic over the soil under my entire crawlspace and do a good job of sealing it to the crawlspace walls and around the supports. That would go a long way toward reducing moisture in the air of the home and moisture damage to the joists/supports/subfloor. Hey, at least the next time you go down there it would be easier to slide around on your back and you'd get less dirty.

(Or, maybe I wouldn't.)

 

[TromboneAl]

I think it would be an all-day job, or longer. Cramped quarters and convoluted paths. Plus the ducts seems to be in pretty good shape.

I've considered the plastic sheeting. Can you really slither around without it coming loose and bunching up (I realize that you staple it down)?

Note that it rarely goes below 45 degrees around here, so one doesn't get moisture buildup due to a big temperature differential.

 

[samclem]

I think it would be an all-day job, or longer.

Yep, it might be. And it wouldn't be a fun day, either. I'll avoid the political commentary, but just say that we are now at the highest national unemployment rate in almost 30 years, and we are both kinda wondering if anyone would be willing to do this unpleasant but not dangerous job in order to earn $50/hour. I will submit that this is perhaps anecdotal evidence that, just maybe, our social safety net is high enough already.

I've considered the plastic sheeting. Can you really slither around without it coming loose and bunching up (I realize that you staple it down)?

I don't really know. I'd probably use those rigid wire hold-downs used to keep landscape fabric in place to "staple" the plastic to the ground, and cover up the staple/holes with some stout tape.

Note that it rarely goes below 45 degrees around here, so one doesn't get moisture buildup due to a big temperature differential.

I think the potential problem you might encounter in your area (air frequently humid) is the water evaporating from the damp soil under the house and causing it to be nearly 100% RH in the crawlspace. Then, when you run the AC, your floor will be a few degrees cooler than the air in the crawlspace, leading to condensation on the subfloor, where the subfloor meets the joists, and maybe in the top layer of the insulation.

Anyway, it's easy for me to think of projects for other people to do. You should see all the undone stuff at my house.

 

[LOL!]

Get some gerbils or hamsters as pets. In no time, you won't be bothered by the smell from your air ducts anymore.

 

[M Paquette]

Get some gerbils or hamsters as pets. In no time, you won't be bothered by the smell from your air ducts anymore.

Ohhhhhhh! You're a bad, bad man!

DD went through the hamster phase many years ago. That room got the 'toxic waste' treatment once the rodents were gone. Yuck.

 

[Nords]

... but it's just too damned cramped down there.

Yep, absolutely no fun unless there's a significant payoff.

That's why my plan is to clean the ducts, mouse-proof the house more, and watch and trap.

I'm OK with cramped, dark, dingy spaces but my keep-me-awake-at-night concern would be how much more damage the critters could've caused before they gave themselves away... for example PEX water piping or ABS drain piping in a ceiling or a wall, electrical wiring (not in use at the time), chewing through a toilet water-supply line, and hantavirus. I'd go through significant discomfort in favor of a "one and done" solution like metal ducting.

I don't know if mice would leave a nice comfy garage for the seclusion of a metal duct. We used to have field mice get into our kitchen by crawling through gaps at the base of our exterior siding, and the only thing that finally stopped them was aluminum foil. We have an ultrasonic gizmo banging away in our garage (as far as I can tell) and it supposedly keeps away the critters, too, although I suspect it's a placebo effect for its owners.

The things around here that really attract rodents are dry pet food and bird seed.

 

[travelover]

..............The things around here that really attract rodents are dry pet food and bird seed.

Years ago I opened the silverware drawer and found it nearly full of the dog's kibble. That must have been a busy night for that mouse.

 

[TromboneAl]

Then, when you run the AC...

AC, what's that? I think that the high temperature last summer here was 66 degrees. I don't think there was one week during which we didn't have a fire in the fireplace.

 

[TromboneAl]

Update

The ducts and furnace are being cleaned now. The good news is that we found the place that the mice got in. There was a place in the ducting in the garage, right under the furnace, where a hole had been taped over. The mice had chewed through the tape. It's right at floor level.



So that supports my finding that there were no holes in the ducts themselves. The tech will make put some metal there.

 

[TromboneAl]

BTW, the duct cleaning was a total waste of money, except for the fact that it enabled me to find the hole that the mice used.

The amount of stuff that was flushed out of the ducts was about a cup's worth of debris. Either all the stuff that was in there was near the registers, and had been vacuumed up by me, or the system wasn't effective at removing debris.

The funny maple syrup type smell is still there, but at about 60% of the original strength. Today I am running the furnace all day with the windows open to see if that eliminates it.

 

[calmloki]

Al - try different stuff: vinegar soaked rags in the air inlet. teaspoon of vanilla bean extract. boil off a pan of coffee in front of the air inlet. All designed to reduce scent.

a common stinky used frig trick is to put a dab of vanilla extract on a cotton ball and toss it in the frig - same thing right under your outlet vents maybe? I like the idea of the vinegar getting sucked through the system - might go so far as to use a mister to schpritz into the air inlet....

ozone generator? good buddies with a car dealer type person?

 

[TromboneAl]

Good idea. I've got the vinegar going through the system now.

 

[Amethyst]

The pictures kept putting me in mind of the colonoscopy thread

Seriously, thanks for the informative discussion and pictures. Ducts and duct cleaning have been on our minds. Our new (very fussy) tenants in our rental townhouse have asked us to have all the ductwork cleaned because they found a wrong-sized furnace filter being used in the basement, and surmised (correctly) that no one had changed it in probably years (since we didn't even know it was there, we are sure the previous tenants hadn't ever changed it). (There is a proper-sized, regularly changed filter behind a vent in the first floor living room).

We have been dodging their requests to have the entire 3 levels of ductwork cleaned "to reduce the risk of fire." These tenants are proving highly creative in finding potential "risks to life or property."

Amethust

 

[ERD50]

BTW, the duct cleaning was a total waste of money, except for the fact that it enabled me to find the hole that the mice used.

The amount of stuff that was flushed out of the ducts was about a cup's worth of debris. Either all the stuff that was in there was near the registers, and had been vacuumed up by me, or the system wasn't effective at removing debris.

A while back, I cut a hole in one of our ducts to add a vent in the basement, and I was surprised how clean it was. Now, If I reach into the ducts near a floor vent in the house, there will be some dust and dirt collected at the bend where the duct rises up, so some dirt falls out of the air stream at that point, which makes sense.

But that got me thinking - if it's clean it does not need cleaning (duh), and if there is some dirt there, well, the dirt is 'there' it isn't getting blown all through the house (otherwise it wouldn't be 'there'). And if that much dust was getting blown around, my filters would be clogging in short order.

Maybe running w/o a filter is a reason to get the ducts cleaned, but it seems unnecessary for most cases.

-ERD50

 

[TromboneAl]

Yes, my advice is to never have ducts cleaned, unless you know there's something in there (such as rodent leftovers).

Here's an update: After running the heat all day, with vinegar sprayed on the cold air return, the smell is still there, but it's coming from only one register. This morning I reached in through that register with a vinegar-soaked paper towel, and swabbed as far as I could reach (in up to my shoulder). The paper towel got quite black, and I repeated this several times. The smell seems better. If it doesn't go away completely, I'll replace that one segment of duct.

 

[TromboneAl]

I removed a 13 foot section that leads to the smelliest duct. There wasn't anything in there but the walls of the duct seemed a little moldy. It definitely had that sweet smell to it. Perhaps we had mice with MSUD.

I'll buy some new ducting and replace that section and maybe some other sections (since I need to buy a minimum of 25 feet.