Water heater performance at altitude

dlhilliard · 03-24-2010, 07:06 PM

As part of my spring cleaning of the FF-189FDS, I happened to read in the water heater operating instructions that taking the FF to altitudes above 4,500 ft. requires the water heater gas burner to be "derated". Since I'm going from about 250 ft. at home to about 8,000 ft. at the north rim of the Grand canyon this Summer, that caught my attention. the manual continues by suggesting that my friendly service department can accomplish a "derating" for me. Does anyone out there have experience in going to high altitudes (without the help of drugs or liquor, of course) with a FF? Do I really need to do this? Is this something that a reasonably intelligent newbie can do? I expect to camp at lower altitudes several days on the way. Can I make this change on-route? HELP!

keyser soze · 03-25-2010, 09:13 PM

Greetings dlhilliard!

This is the first I have heard of this, it goes to show one really needs to read EVERYTHING when ya first buy a trailer! I never thought about it but it makes sense because water boils at a lower temp at high altitude, so maybe they recommend derating it to avoid scalding water coming from the taps. Does this sound right? Or do I have this backwards?

Will update when I have more info...

**LJAZ** · 03-26-2010, 08:10 AM

Keyser you are correct water will boil at a lower temp at high altitude. But I think this is probably more related to the burner performance than the water temp. At sea level water boils at 212 F, go up a few thousand feet and it will drop to maybe 200 F or so at at 8000 ft. I wouldn't think our water heaters would maintain the water anywhere near that temp. I'm just guessing but I would think it would be closer 120 F.

You also have less oxygen at higher altitude so my guess is that derating has to do with adjusting the burner to compensate. Kinda like in the "old days" when you had to adjust your cars carburetor for high altitude. (OK now I'm dating myself!)

keyser soze · 03-26-2010, 09:19 AM

Quote:

Originally Posted by LJAZ

Keyser you are correct water will boil at a lower temp at high altitude. But I think this is probably more related to the burner performance than the water temp. At sea level water boils at 212 F, go up a few thousand feet and it will drop to maybe 200 F or so at at 8000 ft. I wouldn't think our water heaters would maintain the water anywhere near that temp. I'm just guessing but I would think it would be closer 120 F.

You also have less oxygen at higher altitude so my guess is that derating has to do with adjusting the burner to compensate. Kinda like in the "old days" when you had to adjust your cars carburetor for high altitude. (OK now I'm dating myself!)

I see, so you're saying for the proper Air/Fuel ratio the propane should be dialed down a bit to ensure proper ignition, heat intensity, etc. That makes total sense. Thanks LJAZ, appreciate your input! And worry not on dating yourself, I too remember messin with carb jets and ignition points tryin to get a car to run!!

dlhilliard · 03-26-2010, 07:33 PM

I believe the operating manual is referring to an adjustment to the air/propane ratio to compensate for altitude. I tried this question on the Good Sam forum and got about four pages of responses. Most respondees, that have actually gone to the altitudes I'm talking about, say they had no problem even on long stays. One reported that the flame burned a little yellow, which is as I would expect, but they saw no long term damage. Unless I hear otherwise, I'll probably just go ahead without adjusting the mixture and see what happens. After all, I think they have hot showers at the campground.

This should teach me not to read manuals.

By the way, I'm also old enough to remember how to adjust a Holly double pumper and overhaul a Q-jet.

**LJAZ** · 03-29-2010, 03:04 PM

For sure reading the manual is always the last resort!

My guess is that you would only need to do that if you were going to spend the majority of the time at high elevation. Otherwise you'd have to change it back/forth all the time - like in the middle of your trip to the GC and then back again on the way home.

I'll bet you don't even notice any difference. Enjoy your trip!