Mud Daubers and Furnace Screens

[Lumatic]

I am putting in a brand new Suburban NT30SP furnace in my TW. It would be easy and cheap at this point to put in a piece of screening into the inlet/outlet vent. Do you think this would be too much of an obstruction possible create a even bigger problem than mud dauber nests?

PS I do know about the outside the vent screens but they fall off and are a bit pricey compared to a little piece of screen.

[overlander63]

Why not put the screens in the outer vents? 6 screws to get to the screens and deal with them?

[Mike Leary]

Originally Posted by Lumatic

I am putting in a brand new Suburban NT30SP furnace in my TW. It would be easy and cheap at this point to put in a piece of screening into the inlet/outlet vent. Do you think this would be too much of an obstruction possible create a even bigger problem than mud dauber nests?

PS I do know about the outside the vent screens but they fall off and are a bit pricey compared to a little piece of screen.

They "fall off"? These have been on for over ten years, maybe you drive too fast?

[Lumatic]

Overlander, that is what I am thinking of doing but Suburban has "do not block openings" stamped in the outside cover plate. Maybe this is just for the dummies who would fire up the furnace with the vents sealed over.

Mike, I had a pair of those. Now I have a half a pair. Actually I still have a pair, but half of the pair is now rather flattish after I ran it over. $16 for a new pair vs. a buck or less for a little piece of screen. Hmmm.

But if it so cheap to put a little piece of screen in the vent, why doesn't the factory do it?

[dznf0g]

Remember, if you don't use stainless, it'll rust through in a year with furnace use. The pre-made ones cost more, in part, due to the stainless screen and metal.

[Mike Leary]

The factory is paranoid about blockage to the openings, I've had no problems in twenty years and two Suburbans. What you would be well to check on, when the furnace goes in, is ALL the knockouts should be used, otherwise you'll have problems with overheating. The other bomb I'm dropping is the Suburban boards are junk. I think the warranty is two years,so get set to install a "Dinosaur" board after that. I hate to say it, but I'd throw a Dinosaur in upon installation, and keep the dweeb Suburban board as a spare.

Dinosaur Electronics Home. High quality circuit boards for RV appliances.

[Lumatic]

Originally Posted by Mike Leary

I hate to say it, but I'd throw a Dinosaur in upon installation, and keep the dweeb Suburban board as a spare.

About how much does the Dinosaur board go for?

This new furnace is replacing my last NT30SP which replaced the original NT20. In the last NT30 the blower motor housing was badly worn. I figured time/money wise I was better off putting in a new furnace ($400 from Palomino) than messing with the old one. Otherwise all the parts are OK. So I am saving the old furnace for parts, including the board.

[Mike Leary]

Originally Posted by Lumatic

About how much does the Dinosaur board go for?

$100.00 +-, big deal. I carry two spares on board just in case, since they also fit the hot water heater. It's not the parts cost on our appliances, it's the labor required to replace those el cheapo parts that go bad.

[Lumatic]

[QUOTE=I carry two spares on board just in case[/QUOTE]
Boy Howdy! I bet you are a belt and suspenders man. Me, I'm lucky if I can find my BVDs in the morning.

[Mike Leary]

Originally Posted by Lumatic

Boy Howdy! I bet you are a belt and suspenders man.

When you full-time,especially with an Airstream,stopping at Goober's R.V. repair is not an option without the proper parts and experience.

[Steve Bryant]

On the mud dauber topic, I think that most any screen you could buy at a hardware store would be too fine, too obstructive and not up to handling the heat and corroding effects of the exhaust. I highly recommend the commercially available mud dauber screens. I've owned three travel trailers over the past two plus decades and have locked horns with the little critters twice regarding furnaces (see http://www.airforums.com/forums/f427...ace-86137.html for details on one encounter).

[Lumatic]

I sent this question to Suburban FYI this is the response:
1. Any screen creates too much restriction for the furnace
2. If a furnace is used with a screen the warranty is void
3. Take screens off when the furnace is being used.

I wonder if my installing the furnace and not being a certified tech also voids the warranty?

[dznf0g]

Originally Posted by Lumatic

I sent this question to Suburban FYI this is the response:
1. Any screen creates too much restriction for the furnace
2. If a furnace is used with a screen the warranty is void
3. Take screens off when the furnace is being used.

I wonder if my installing the furnace and not being a certified tech also voids the warranty?

A "liability" response, IMO. I have NEVER run into anybody who has had issues with the large opening stainless fabric of the commercially available covers....for decades!

[Steve Bryant]

Originally Posted by dznf0g

A "liability" response, IMO. I have NEVER run into anybody who has had issues with the large opening stainless fabric of the commercially available covers....for decades!

I agree. Since they don't have any control over the variables of screen installation, etc., the best way to limit potential product liability/warranty issues is to publicly state that screens should never be used. If I were their legal counsel (glad I didn't become a lawyer), that would be my recommended standard party line on the use of screens. In fact, if you modify any manufacturer's product while under warranty, that modification typically will void any warranty.

At the end of the day, I'm going to install commercially available screens. No problems with screens for me in the past.

If you looked at my thread on mud daubers, you'll see that they have caused problems for me in operating the furnace without screens.

[0557]

Made these for my suburban, used #14 stainless screws to hold them in the center, cost $1.50 and 30 mins labor.

[Protagonist]

One reason why commercially-available screens have a dome shape rather than being flat is called "equivalent opening size." By making them in a dome shape, you can make sure that the total size of the screen openings is as large or larger than the furnace exhaust opening. This ensures that the screen does not create an obstruction. The larger the mesh size, the smaller the dome shape needs to be to provide the right equivalent opening size.

The flat screens that 0557 made do provide an obstruction to the exhaust. The equivalent opening size is reduced by the wires of the screen. His screens may work for him, but as a mechanical engineer, I can't recommend it.

[0557]

They do work, and can be removed in the winter
when wasps are not building nests.

[Protagonist]

Originally Posted by 0557

They do work, and can be removed in the winter
when wasps are not building nests.

If you remove the screens before firing up the furnace, that's a different case. If you're going to do that, why use screen at all, when a solid metal cap will not only keep out wasps, but keep out water or dust as well? After all, you could remove a solid cap just as easily as you remove a screen.

[0557]

I typically use 3 inch foil tape for that

[Aage]

I remember when reading the owners manual for the new Suburban I installed last spring that they specifically mentioned not to use screens over the intake and exhaust.

However, if one remembers to remove them before use it obviously wouldn't be a problem.