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Old 07-06-2004, 04:31 PM   #21
Rivet Master
 
LOST , Hawaii
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Is a typical rv water pump rated for hot water use?

Can it pump through 300 ft. of 1/2" pex?

How are you going to switch the pump between the potable water and the heating system? Check the price on 12v solenoid operated 3 way valves, that will blow your budget.

How will you winterize 300 ft. of pex?

What are you going to do for heat for the holding tanks?

John
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Old 07-06-2004, 05:17 PM   #22
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"maximum of about 25 btus of heat output from the hot water per square foot of floor panel. That means that 100 square feet would only need about 2500 btus from the water heater."

to get the same amount of heat in the trailer as a typical furnace that means you would need about 1000 sq feet of this sort of heating.

to get the same amount of heat as a typical 110v space heater, which will barely help prevent pipes freezing in 10F - 20F weather, you would need 500 sq feet.

What I infer from the 2500 BTU (per hour assumed) per 100 sq feet is that floor radiant heat is a difficult way to move heat from water to a useful form. That makes me think you might be able to get a somewhat warm floor but keeping the water lines from freezing under the sink is going to be a problem. I am very curious to hear about how it works out in practice.
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Old 07-06-2004, 06:06 PM   #23
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i appreciate that you did some investigation.....and that now you probably realize that the idea of radiant heat will only be a means of making the inside of your coach a more even temperature..... in short this is only a auxillary system and if you want to do it, go for it, but my gut reaction is that you are trying to piss up a rope....once again as someone else on the forum has stated..."there is a fine line between a hobby and insanity"......
norby
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Old 07-06-2004, 06:13 PM   #24
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All good questions...

John,

I don't know if a standard RV pump has the necessary capacity - I have to find out more about that. I don't actually have to switch between potable and heating water. The system I am envisioning is a so-called "open system". This means that potable hot water is pumped out of the water heater, through the heating pipes and back to the water heater. The PEX tubing is fully qualified as potable - in fact it is exactly what someone would use to plumb their potable system if they chose to use plastic rather than copper. So a 3 way valve is not needed. All I need is to open a valve to the heat tubing when I want heat and get the pump to turn on - or maybe I just need a second pump for the heating system that would in esscence work as the valve too.

Winterizing is no harder for 300' of PEX than it is for anything else. I just have to make sure I can either drain or blow out the water. As for heating the holding tanks I could probably run a loop of the tubing by them. There might also be enough residual heat passing down through the floor to do the job.

Malcolm
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Old 07-06-2004, 06:25 PM   #25
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2500 BTU was what was needed...

Bryan,

I think you may have misinterpreted what I said about the 2500 BTU's. I asked the guy I was talking to to give me an idea as to how much energy I was likely going to need to supply from the hot water heater to heat the area serviced by the panels - I wanted to uderstand the loading on the water heater. His reply was that the radiant heating system is an extremely efficient means of heating people and that only about 25 BTU's per square foot of floor panel would be consumed from the water heater. He was not at all saying that this was all that the panels could transfer to the room - he was just giving me a guestimate as to what would actually be consumed by the panels in their cycling on and off over time in the process of heating my AS.

In actual practice hot water radiant heating systems are considered to be one of the most efficient ways to heat space. Also note that the PEX tubing is in close contact with large aluminum sheets that entirely cover the heating panels over most of the path of the tubes. The heat transfer mechanism is way more capable of transfering BTU's to the space than would ever be needed in practical usage.

Malcolm
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Old 07-06-2004, 06:30 PM   #26
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With all due respect...

Norby,

With all due respect I don't think you have a clue as to what you are talking about when it comes to radiant heating. My investigations do not lead me to the conclusions that you are suggesting at all. Perhaps you were swayed by Bryan's missunderstanding of the 2500 BTU's?

As far as there being a fine line between a hobby and insanity goes I can only quote the following:

"Only he that attempts the ridiculous can acheive the impossible".

Malcolm
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Old 07-06-2004, 07:35 PM   #27
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a noble quote...actually you unknownly will be achieving what is known as a 2 stage system if you keep your forced air system....cost factors usually dictate only a one stage system...given that cost seems to be no object.... i applaud you and wish you well in your endeavor...
norby
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Old 07-06-2004, 08:14 PM   #28
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Quote:
Originally Posted by malconium
As far as there being a fine line between a hobby and insanity goes I can only quote the following:

"Only he that attempts the ridiculous can acheive the impossible".
Malcolm
I have to say I know NOTHING about radiant heating, but it sure looks to me like a solution in search of a problem. Then again, I will not criticize you if you promise not to make fun of some of the stuff I have done to my coach.

The question about valving and the water pump is, I think, related to the necessity of the pump to deliver hot water, cold water, and to circulate the heated water. I am finding it hard to envision how this can be done with a single pump.

Are you serious about the 300 feet of tubing on the floor, or is that just how much tubing comes in a roll? I don't think we have space for anything like 300 feet of Pex on the floor of any Airstream. Whatever it is, I think you underestimate the difficulty of truly purging that much tubing. You may want to consider some intermediate drain valves.

Finally, the roar of my water heater is not significantly quieter than my furnace. It likely depends upon location - mine is right under our bed while the funace is up near the front. I turn the water heater off at night as it wakes me when it fires up.

Mark
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Old 07-06-2004, 08:14 PM   #29
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No existing systems...

Quote:
Originally Posted by norbert
a noble quote...actually you unknownly will be achieving what is known as a 2 stage system if you keep your forced air system....cost factors usually dictate only a one stage system...given that cost seems to be no object.... i applaud you and wish you well in your endeavor...
norby
As a matter of fact my AS is in need of replacements for most everything. I need to replace the wather heater, water pump and the heating system anyway. That is part of the reason that I am taking a closer look at my options. If I go with radiant heat my intention is to not replace the forced air heater at all. I wouldn't mind recovering the space under the kitchen sink.

Malcolm
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Old 07-07-2004, 12:08 PM   #30
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Quote:
Originally Posted by malconium
I don't actually have to switch between potable and heating water......So a 3 way valve is not needed.
Ah, but it is. You need to get a pencil and paper and draw this out.

Normal operation takes the water from the freshwater tank, to the pump, then splits to feed the water heater and cold water systems.

Your system is doing nothing more than recirculating water.

How are going to get water to the cold taps if you don't draw it from the tank? The only way to do that and recirculate hot water with the same pump is a 3 way valve.

John
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Old 07-07-2004, 12:19 PM   #31
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Malcom, thanks for the attempt to clarify between maximums and average needs.

"the radiant heating system is an extremely efficient means of heating people and that only about 25 BTU's per square foot of floor panel would be consumed from the water heater."

Where I am still puzzled, though, is that there is such a discrepency between this rate and that typically found in RV heating systems. Even catalytic heaters, another form of radiant heat, produce significantly more heat and they are not considered suitable for entire RV heating.

I do think you will need an additional pump, though. But it still sounds like an interesting experiment and I hope you will continue to share what you find out with us.
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Old 07-07-2004, 01:35 PM   #32
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Probably a second pump...

Mark made a good point about the location of the main water pump in an RV which I had not entirely thought out. The more I think about it the way to go would be to have a second pump just for the hot water heating. With a second pump I would not expect to need a valve. When the pump is off the hot water will not be moving around the heating system. I suppose it would be a good idea to consider shutting off the heating system from the rest of the water system during the warm months or at least circulating some water through them from time to time to keep the water there from stagnating.

The 300 feet of tubing is what comes in a roll. The insulated floor panels actually take 2' per square foot of panel. The tubing is deployed on 6" centers.

Is it strictly speaking necessary to drain all the water out of the plumbing? It seems to me that if most of the water is out the remaing water would freeze and expand in the path of least resistance - namely into the area not filled with water. Also I should note that I live in Portland, Oregon where the problems with pipe freezing is not as bad as some places I could think of.

A couple of questions occur to me as follows:

1.) Is there any reason I couldn't leave my water heater and floor heat turned on when I am driving if it is really cold outside? That would relieve the potential problem of the thermal lag time if I left the heat on at some lower maintenance level. If I could do that I might very well be tempted to install the radiant heat tubing under the plywood floor instead of above in the insulated panels. It turns out that this approach would actually be a good deal less expensive (a savings of perhaps $300 or $400). Instead of using the insulated panels you use strips of aluminum that are 5" wide and grooved to snap onto the PEX tubing. The tubing is laced around under the floor and the aluminum strips are snapped on from below and stapled to the bottom of the floor. Relective foil insulation is commonly used below the tubing for this type of installation - which is what I had intended to do anyway. Heat under the floor would also take care of the plumbing and holding tanks pretty well I would think. I probably would deploy the heating over the whole floor area as well.

2.) Is there any reason that I could not move my water heater to the location where my forced air heater used to be? The heater used to be on the curbside under the kitchen sink. Besides the obvious fact that I would have a big hole to fill where the water heater used to be is there any other reason that this would not work? This would get the noise away from the bedroom - yes my water heater location is under the bed too.

Malcolm
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Old 07-07-2004, 02:27 PM   #33
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Quote:
Originally Posted by malconium
Is it strictly speaking necessary to drain all the water out of the plumbing?
1.) Is there any reason I couldn't leave my water heater and floor heat turned on when I am driving if it is really cold outside?
2.) Is there any reason that I could not move my water heater to the location where my forced air heater used to be?
Draining plumbing-absolutely. You are talking about a lot of water that could be left in the tubing. If you get the trailer absolutely level it would be just a small amount laying in the bottom. A slight angle will put it all to the low end and leave no room for expansion.

1.)The belly pan is not airtight, you will probably affect the flame with the air flow because of the speed of the trailer.

2.) Move the water and gas, make a new hole, patch the old. Not that big a deal with a little ability.

John
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