furnace venting

[Myke]

I was looking at my furnace today and discovered a problem. The furnace is out of an old pop up. It is designed to be set against an exterior wall, obviously. The problem is, I need it under the full bed blowing out into the area between the doors and towards the twin bunks in back. To do this the exhaust would be about 3 feet from the front wall. Can I use a dryer vent to exhaust the fumes out of the camper? The only other way I could use the furnace is to go with one door, and I really want to have 2 doors. I'm sure a dryer vent would hold up to the heat of exhaust, but does a pop up furnace blow the exhaust, or does it require being on an exterior wall to suck the fumes out?

[Miriam C.]

When in doubt leave it out! Not for anyone's money would I put one under my bed. Do you have a space over head to put it? Don't know about the venting. My guess is it is pulling in fresh air and exhausting, both from the outside.

[Elumia]

search the internet for a manual? Seems a good place to start. Must be a nameplate with a Mfg and Model #

Mark

[48Rob]

More information is needed about the brand/model of furnace.

Many produce very hot exhaust.
A dryer vent might work for some, and might burn your trailer down if used with others...

I needed to extend mine (the exhaust) just throught the 3/4" plywood wall, a distance of about 4 inches.
I used a steel automobile exhaust pipe, with a brass outer pipe to create a double wall pipe.
I also have a metal "dish" around the pipe to further separate the wood from the pipes.
It is designed to draw air through the space between the pipes.
It keeps the outer wall pipe temperature at 110 degrees where it contacts the plywood.
The inner pipe hits 200 degrees plus.
The upper pipe is exhaust, the lower is intake.

<img src="http://w48rob.wik.is/@api/deki/files/205/=furnacevents2.jpg">

[Mark McD]

Seems to me you have three things to consider- all are very important issues.First- clearance to combustibles. Every gas or lp appliance will have the info listed someplace on it. You may not be able to mount the heater under a bed because of the clearance to combustibles. 2.)Combustion air. Your heater needs an adequate supply of make-up air- usually from an external source- otherwise the unit will burn all the available oxygen from inside the camper and if it's not equipped with an Oxygen Depletion shut-off, as many older units are lacking, it will suffocate you.You need to check the manufacturers specs on how far the intake can be from the unit. If it's too far, it may not have a powerful enough motor to pull in sufficient combustion air.3.) Exhaust. The manufacturer will also specify how many cubic inches of exhaust duct the unit can have- because like intake air- the motor may not be powerful enough to push the exhaust down a long tube to the outside, potentially causing a backdraft. You may be able to duct it out and use a fan to make sure the exhaust is expelled out completely. And use hard-pipe,(metal), to duct it, dryer vent hose is too thin.

[35thAV]

search the internet for a manual? Seems a good place to start. Must be a nameplate with a Mfg and Model #

Mark

I agree, I would at the very least make a call to the manufacturer before I risk burning down my little box or risk suffocating the family!

Mine uses a double wall pipe the inner pipe is for exhaust and the outer portion is the fresh air intake. If this is the case on yours you may want to go with something like 48Rob described to be safe.

[brian_bp]

Direct-vent furnaces, in which the exhaust, intake, and the furnace itself are all at approximately the same level, can't use the "draft" of a traditional flue so they do include a fan to push the combustion air....

however, there is no way I would extend the exhaust except as specifically allowed by the manufacturer. Personally, I doubt dryer vent - which is intended for air that is not as hot and does not have combustion gases in it - would be suitable in material or construction.

An option might be to extend the interior side, with heated air outlet and return air inlet ducting, just like a home furnace. The fan in the furnace may not be adequate to move the air through the extra ducting (some people extending air conditioners this way have found they need boost fans), so even this approach is problematic.

[Mark McD]

Yes, backdraft may have been the wrong term. I should have said...having the potential to cross contaminate combustion air and exhaust air- given the fact that the velocity of expelled exhaust would be low and most likely be recycled back in as combustion air.?
In other words your combustion,(fresh air), would just be recycled exhaust gas. Not good unless you like headaches and CO2 induced hallucinations.

[Myke]

Thanks for the advice, I "was" sure dryer vent would work. I think all my postings should be titled, "Protect me from my Stupidity" I'm trying to convince the wife to go with the original plans.

[48Rob]

Myke,

Don't be hard on yourself.

You had a reasonable idea and went looking for more information to determine if it might work.

"Stupid" is one who has an idea and implements it without regard to practicality or safety.

If you "need" a furnace that fits under a bed, keep looking, there may be one out there, pre made, or that can be safely adapted to fill the need.

That said, I would caution that while the location may be good for saving space, the blower that doesn't seem too intrusive during the day while you're testing it, will transform in the dead of night to sound like a jet airplane taking off next to your ear...

Rob

[Miriam C.]

There are no stupid questions

Have you thought of putting the heater on the tongue. You can pipe the heat in with a dryer hose.

[DrCrash]

Just an idea. How about a Petcool, has a built in heater that wont kill ya and airconditioning.

[35thAV]

Would it be possible to mount the furnace at the wall so the exhaust/intake is the correct length then use a vent pipe to vent to warmed air out into the sleeping area?

Our old travel trailer was setup this way from the factory it had the furnace mounted in a cabinet aginst the wall with direct venting out side then used two vent hoses and three adjustable wall vents to expell the warm air out at three different places inside. One of them was a good 8' away from the unit.

I guess it depends on what unit your working with.

.

[WarPony]

<img src="http://w48rob.wik.is/@api/deki/files/205/=furnacevents2.jpg">

Rob, I have a couple of questions for you. First, what kind of furnace do you have and do you have any pics of it?

Third, are you concerned about drawing CO into the intake pipe when it is so close to the exhaust?

We bought a brand new Atwood Everest Star II last year to install in our Widget build and this REALLY has concerned me from the begining.

Jeff

[Dean in Eureka, CA]

Myke,
It sounds like you have an Atwood type furnace... Very common in small RVs.
Besides your exhaust duct/vent, there should also be an intake duct/vent.
Both of these have nothing to do with the supply and return air vents on the interior cabin space.
The intake supplies fresh outside air for the burner and the exhaust blows hot gases from the burner to the outside.
Dryer hose is not suitable for exhaust ducting, but double wall sheetmetal vent pipe and in some cases, single wall is too, but you need to check with the manufacturer to find out.
You should be able to accomplish your plan by using a 90 degree elbow in the exhaust vent pipe and probably just an access space to the outside for the intake air.
Call the manufacturer and tell them what you have and what you want to do... Get their reccomendations before throwing in the towel on this.

Believe it or not... Some of the newer high efficiancy furnaces I install, now use PVC exhaust vents, even in horizontal venting applications.