Something else to do before the furnace comes on

[Ozz]

Greg, sometimes we have to balance the practical aspects of something like this, In my 3400RL, most of the dust, cat hair, airborne junk comes from our living area, so filtering the air from there is 90% of it.
My return is right under the stairs, not sure where yours is on your unit. Take a cigarette, or a smouldering...something, and hold it where you think the air might be going back to the furnace, the smoke being sucked away will show you.

[Ozz]

quote:Originally posted by Wild Horse

we now use the WEB vent filters made for register filtration..we use these in the new adjustable registers, and they work fantastic. 4x12, can be cut down...a 12 pack is cheap. also have the return air filtration as well.

I am not a big fan of register filtration, one, it restricts airflow and produces back-pressure on the fan. That raises the amp draw on the fan, overheating it. Probably won't do damage, but it really depends on how much it is restricted, in this poorly designed system, you might even pop off a supply run.
The second thing is that you want to protect the furnace from dirt-dust-hair and so on, do this by a return air filter, not a supply filter, after all, what goes into the furnace returns to the space. If you filter the return air, the supply air will be clean. I know there is crud in the heat runs from the build, but anything that will be airborne should be out in the first 50 or so hrs. of running the furnace.
Also, the adjustable registers (I have) restricts the airflow about 20%, I cut the dampers off mine, for full airflow. Makes a difference. I kept the registers because they are wood and look nice.

[Gkerlin]

quote:Originally posted by Ozz

Greg, sometimes we have to balance the practical aspects of something like this, In my 3400RL, most of the dust, cat hair, airborne junk comes from our living area, so filtering the air from there is 90% of it.
My return is right under the stairs, not sure where yours is on your unit. Take a cigarette, or a smouldering...something, and hold it where you think the air might be going back to the furnace, the smoke being sucked away will show you.

The smoking gun was going to be my fall back idea if someone with a 3455sa doesn't reply.

Looks like I might have to start smoking again.

[Irlpguy]

I don’t know where your furnace is located in your model Greg, however I suspect it is very little different than my 3402RL which is located next to the hot water heater.

Sadly these furnaces are not built like the ones in our wooden houses, if you take off the cover of your furnace on the outside you will see a squirrel cage fan with a 6” diameter fan, the fan itself is made of plastic and only has ¼” high vanes, therefore it must turn very fast to provide the air required to move it to the back of the RV. You will also notice that on each side of the burner compartment there is an opening for air supply to the fan, there is also an opening behind/above the circuit board as well. These do not go anywhere except into the large compartment behind the furnace. That means they can draw air from the storage area, the whole area under the shower bathroom and the underbelly itself.

If you consider the amount of space there is in the basement and compare it to the rather small openings to the living area at the two steps you will find that it is minimal compared to the overall area. It is also a considerable distance from the furnace air intake.

You can put filters on the back of those step openings which will eliminate any dust and so on coming from there, however the vast majority of air is coming from the large open spaces around the furnace and is not coming from your living area.

There are actually two fans combined in one on these furnaces, the larger one pushes air past the burner tubes for heat and the other one in the lower sealed compartment blows air out the exhaust vents in the bottom of the vent panel. This is meant to move the exhaust away from possible intake into the furnace.

You would have to be very small and dexterous to get in the area of the furnace to modify the intake to resemble what we have come to know in our S&B’s. It could be done but would be a very difficult modification.

Because of the size of the furnace fan we have to put up with the noise of it turning so fast, a larger fan turning slower would produce the same amount of CFM and would be much quieter. It would not be all that difficult to build a dual voltage feed to the motor to control the speed of the motor and place the switch in a convenient location, however while it would slow down the motor thus reducing the noise, unfortunately it would also reduce the air flow proportionately.

I hope the above gives you a bit more of a perspective as to where and how the furnace gets it’s return air, and a better understanding on the limits of return air filtration.

[DQDick]

Still, those who put the filters under the stairs find that a lot of hair and dirt accumulates, particularly if you have pets, so it's a good thing to do even if it isn't perfect.

[granet]

Special note for all those who are really winter camping;
Ive just found out the hard way that dometic fridges crap out if the weather is colder than 10 below.The brine system they use gells up.So insulate your vent covers,hang a troble light back there and block the breather tube till the weather gets above zero. I just had to replace my 5 year old fridge because of this.
Regards
Granet
2008-3400rls
Canadian Rockies

[Gkerlin]

When I installed my solar this fall and had the basement wall off - I vacuumed out the mess that was left in there at the factory so that is at least a step in the right direction I guess.

I'll try to make a fiberglass type filter for the steps and see what sort of critters I can catch.

[Ozz]

Ed, the outside air does not come inside, the furnace pulls air form outside and exhausts it, the return air gets sucked in the furnace and expels out the furnace end, where the ducting is. The large area around the furnace is return air, but no outside air should be allowed in that space. That air comes from the living area, it just circulates, except the air going down under the unit.
If I understood your post correctly.

[Irlpguy]

Ozz, I do not see where in my post you think I suggested outside air was used in supplying the return air for the furnace. I make no such suggestion in fact I stated the two fans are in separate sealed compartments independent of one another.

The compartment that encloses the “burner tubes” through which the fan pushes air to the registers is quite narrow in fact is only 5” wide at the top, 7” wide at the bottom and 17” high by 10” deep. As you can see in the picture below there is 1” on either side of the upper half of this compartment open to the main fan and the basement area, as well as the black grate sort of thing on the top, which I referred to in my previous post as being behind/above the circuit board. This also supplies air to the main fan.



The picture below was taken from inside my storage compartment, it shows the large area from which the fan can draw air, representing a much greater area than that opening below the steps leading into the living area.



As I said in my previous post, one could put filters behind the step openings which would keep things from going into the basement area. Anything kept out of the basement will not be drawn into the fan so there would certainly be that benefit, but it by no means filters the air to the return air intakes.

The OP referred to vacuuming the vents and the amount of “stuff” that gets into these vents from everywhere. It was your post Ozz that suggested filtering the return air which led to descriptions of what some have done to try to combat the problem, I find no fault with any method one might employ, I merely tried to explain how the furnace works, where it gets it’s return air to help folks see how limited the ability is to filter the return air.

I hope these pictures add further to understanding what I have been saying.

[Ozz]

OK, I said IF I read it correctly, guess I didn't. Sorry.
Too involved for my Pea brain I guess.
Ozz

[Irlpguy]

Ozz, with your background in the business I am sure that you could figure out a way to put a filter in the system, I myself could do it if I had a sheet metal shop and the room to move things around in the area of the furnace, a slide in and out filter would be a simple modification were there room to do it. I have built several filtration systems for computer network servers at shops that had a very dusty, dirty enviornment, I simply used furnace filters as the filter medium.

If the Monty was to be my full time home I would be looking seriously at making such a mod. It really is a pretty crappy heating system, no worse, and no better than any of the other brands, and there is not much new innovation going on in the field of RV furnaces.

Everyone should do whatever they feel comfortable with to help eliminate things from getting into the return air for the furnace, simple, no judgement here.

[Ozz]

The way I look at it, all the potential airborne materials are already sucked out of the space around the furnace. I would not worry about that.
The living space, where the dust, cat hair, dog hair, what ever is bright in from outside, is constantly generating dust... and is circulated.
Where the filter is needed is between the living space and the furnace. In my case, the space under the stairs is the return air area from the living space, the furnace blower 'changes air' (guessing but close)...7 times an hr. (Your home changes air around that figure) The area around the furnace will be scrubbed by this filter, but it is of no consequence, since it no longer generates dust, or any airborne materials of any consequence.
Here is my pleated filter. It does not restrict the airflow.

[Irlpguy]

Looks like a newly installed portion of a regular furnace filter, it will keep a lot of "stuff" from migrating into the basement area. I have a dog and have had those grates off the steps several times and have found no dog hair beyond the grates but I am not living in my unit even close to full time.

Personally I don't find the whole filtration thing a real big deal, having said that my opinion might change if I were full timing. I vacumn out the vent area's at least once a year and find most of what is there comes from dropping down the register not pushed there by the fan. We visit the Yuma area each year and there is a lot of airborne particularly on windy days, this finds it's way into the unit and the majority of the time we are not running the furnace to spread it around. It just gets in and settles everywhere.

Ya just gotta do what ya gotta do, that's all.

[Ozz]

Working with heating and air conditioning systems, I see all sorts of neglect by the homeowner, some never change the filter, and when the system fails, they usually pull the clogged air filter because the system freezes up in the summer, or the high limit switch keeps the heat off in the winter sometimes they just don't put one back in.
Here is a dog-hair sweater I pulled out of one unit, it was completely wrapped around the A-coil, the dry, light color on it was the top of the coil.
You may not see a big deal out of filtration, I do. In our RV's the lint, and dog hair just wraps around the heat exchanger, cooking when the heat is on. I like to breathe the air as clean as I can get it.
Here it is.

[Irlpguy]

The filth in that filter only demonstrates the disgusting conditions those people must have lived in. They obviously did little or no housecleaning.

I feel I am entitled to voice a personal opinion regarding filtration in my own RV, I expect to do that without criticism from anyone for doing so. As the "expert" on all things heating and AC Ozz, you can place filters in your RV wherever you want, I will not criticize you for doing so, and have not done that.

Go back and read my posts on this topic, they were intended to help others through my observations and pictures see the limitations in filtering the air in our RV's with the system we have. I did not downplay any efforts to eliminate dust in anyone's RV or their method of doing so. You have jumped on each of my posts in an apparent attempt to make me look bad, why I do not know, but I take it as a personal affront.

Now get off your high horse and go hide a cache or something.