DIY radiant heat system

[seayaker]

I'm exploring the possibility of making a radiant floor heating system for a RV or van with a propane tankless water heater. I've been using a 12 liter per min. heater in a RV for years and am very happy with it. I just wonder how efficient it would be if I got a water pump and some pex tubing and made a closed system. The heater seems to be very efficient for my hot water so I just wonder if it would be worth while to make a heat system. I like the idea of having the heater outside where no fumes would get in and pump the hot water through the tubing. Any thoughts on how efficient it could be. I'm not at the point to do mathematical calculations just looking for a semi educated guess.

 

[LittleInch]

If you don't have the height or you want more heat you can always blow air sideways through it.

 

[seayaker]

If you don't have the height or you want more heat you can always blow air sideways through it.

I've been looking for some tubing, (stainless is spendy) best I found so far is this.

1" OD 304/304L Stainless Steel Tubing, 16 Gauge (.065), Welded, A269, Mill ID, Bright Annealed​

would annealed effect the heat transfer? I can get enough for 6 18'' tubes for $50 what do you think?
I really like this design, thanks for your help

 

[dvd]

What is the flowrate of products of combustion at flame temperature? What will be the velocity through your tubes based on the flowrate? How long does it take for this to get through the system? Can you recover as much heat as desired? You will need to do a few calculations to get a feel for how successful this may be, and then you'll probably be lucky to get a +/- 50% guesstimate.

 

[seayaker]

What is the flowrate of products of combustion at flame temperature? What will be the velocity through your tubes based on the flowrate? How long does it take for this to get through the system? Can you recover as much heat as desired? You will need to do a few calculations to get a feel for how successful this may be, and then you'll probably be lucky to get a +/- 50% guesstimate.

How efficient are these guesstimate?
https://vancafe.com/propex-hs2000-6...uGcEYsnTW1pxCuk4s7WLrNEUx818mBEBoCD-AQAvD_BwE

 

[dvd]

I have no way of knowing - good luck with your investigation.

 

[seayaker]

I have no way of knowing - good luck with your investigation.

Just use the same level of expertise you used to come up with probably be lucky to get a +/- 50% guesstimate.

 

[LittleInch]

I've been looking for some tubing, (stainless is spendy) best I found so far is this.

1" OD 304/304L Stainless Steel Tubing, 16 Gauge (.065), Welded, A269, Mill ID, Bright Annealed​

would annealed effect the heat transfer? I can get enough for 6 18'' tubes for $50 what do you think?
I really like this design, thanks for your helpView attachment 3978

Don't know. The heat will discolour the tubes pretty fast, but shouldn't affect the heat transfer.

Just note that the tubes will be very hot at the bottom end especially.

Let us know how it goes.

 

[IRstuff]

Adding fins on the inside and outside will substantially improve the heat transfer efficiency.

Note, however, 6 1-in tubes has only 37.5% the cross-sectional area than a single 4-in tube; you'd need 16 tubes to get the same cross-sectional area to get the same air flow, but even then, the flow friction coefficient be at least 4x worse.

 

[LittleInch]

Start off with a fairly small burner.

 

[seayaker]

Start off with a fairly small burner.

Adding fins on the inside and outside will substantially improve the heat transfer efficiency.

Note, however, 6 1-in tubes has only 37.5% the cross-sectional area than a single 4-in tube; you'd need 16 tubes to get the same cross-sectional area to get the same air flow, but even then, the flow friction coefficient be at least 4x worse.

Adding fins on the inside and outside will substantially improve the heat transfer efficiency.

Note, however, 6 1-in tubes has only 37.5% the cross-sectional area than a single 4-in tube; you'd need 16 tubes to get the same cross-sectional area to get the same air flow, bu

even then, the flow friction coefficient be at least 4x worse.

''fins on the inside and outside'' ? like this? 37.5% is significant isn't it?
I don't plan on doing anything till summer so plenty of time to work things out on paper.

 

[LittleInch]

That would work if you're planning on blowing air sideways through it.

If you're relying on natural convection then the fins need to be vertical.

See my original sketch.

 

[seayaker]

Something like this? What about more tubes smaller diameter? This would take a lot of brazing.

 

[LittleInch]

It's about increasing the surface area so both are good.

You prob only need two fins per tube and you can stitch weld/ braze.

Or use square or rectangular tubes? Would make it easier.

You do need to think about the gas flow of the hot gases so a few larger tubes is better for that.

 

[seayaker]

It's about increasing the surface area so both are good.

You prob only need two fins per tube and you can stitch weld/ braze.

Or use square or rectangular tubes? Would make it easier.

You do need to think about the gas flow of the hot gases so a few larger tubes is better for that.

Thanks, makes sense. Will depend on cost and what I can find.

 

[seayaker]

So

Thanks, makes sense. Will depend on cost and what I can find.

So I took the burner out of the old water heater, it still works fine. The calanoid opens the gas when 3 volts are applied. The flame sensor works but I had to order a signal amp module to get it to 3 volts. I have access to some 3/4'' stainless steel tubing, enough to build it as in the sketch. My question is would it be possible to press fit the tubes into 1/4'' aluminum as apposed to brazing into thin stainless? Would the 2 metals expand differently and open up? Also if you think this would be good spacing for the tubes?

 

[LittleInch]

So

So I took the burner out of the old water heater, it still works fine. The calanoid opens the gas when 3 volts are applied. The flame sensor works but I had to order a signal amp module to get it to 3 volts. I have access to some 3/4'' stainless steel tubing, enough to build it as in the sketch. My question is would it be possible to press fit the tubes into 1/4'' aluminum as apposed to brazing into thin stainless? Would the 2 metals expand differently and open up? Also if you think this would be good spacing for the tubes?

Maybe, but you don't want to much gap for the flue gas to leak out.

Spacing looks ok but think that burner is just far too powerful. You probably only want 2 or 3 out of those 6 burners.