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Upside down radiators.


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If the circulating water flows in and out at the top of the radiator, they will not get hot because the cold water in them will stay put at the bottom (which is all of the radiator)

Would this also apply if one uses Deuterium Oxide, aka Heavy Water? Sorry, was this a serious question?

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Would this also apply if one uses Deuterium Oxide, aka Heavy Water? Sorry, was this a serious question?

 

 

Hmmm, not sure about that one. Probably not, as the thermal coefficient of expansion is less for deuterium oxide at 0.000172 than with ordinary water at 0.000253

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Your answers are as i expected but i popped onto a boat to look at an engine problem for a guy and got talking about heating.He has rads upside down that were plenty hot...odd.

 

Thanks .

 

That's odd, I'd expect them to be quite cold towards the bottom (of the radiator). Maybe the flow rate is high enough to stir up the water in the rads (now I'll stand back and let someone who knows more than me about it, of whom there should be many, explain the real reason.

 

Both our domestic and boat radiators have the inlets and out lets at the bottom of the rads and they still get hot.

 

That's normal.

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Hmmm, not sure about that one. Probably not, as the thermal coefficient of expansion is less for deuterium oxide at 0.000172 than with ordinary water at 0.000253

Oh yes, of course, silly of me,..but how does the coefficient of linear expansion vary in a fluidic state when (a) under pressure or (b)subject to latent heat of vapourisation....I forget. :help:

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Oh yes, of course, silly of me,..but how does the coefficient of linear expansion vary in a fluidic state when (a) under pressure or (b)subject to latent heat of vapourisation....I forget. :help:

 

Is this a central system, or a small thermonuclear power station in disguise? (what percentage propulsion do you declare on a PWR system?)

 

I had assumed that the system was not pressurised, and if the water in the system is vapourising it's probably time to turn down the thermostat.

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The water in the radiators on our boat is fed into the top and exit from the bottom, as indicated in the installation instructions from manufacturer of the Gas boiler (Ellis Heatmaster) The small one gets hot throughout, but the long one is never hot at the bottom, and I have been considering replacing it with two shorter ones in the hope of increasing output.

 

As a matter if interest one of the radiators only had one threaded connection at the top, and that was used for the input, so when I re-fitted the boat I reinstalled it upside down so that I could fit a bleed valve. Radiator function actually improved a little, but only because I was able to expell all the air, it still stays fairly cool at the bottom.

 

Most modern radiators seem to have threaded connections at all four corners, so (apart from appearance), there should be no significant difference in performance.

Edited by David Schweizer
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Heaven knows how he bleeds them then!!!

 

He won't need to if the feed pipes and connections are at the top of the radiators. Air will rise to the top of the system and need to be let out there, either manually or via an open vent pipe.

 

MtB

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Most modern radiators seem to have threaded connections at all four corners, so (apart from appearance), there should be no significant difference in performance.

 

Sounds correct..?

 

The bottom ends are for inlet and outlet..the top two...are to give you the option of which end you want the bleed screw..the other end being blanked..

 

My dad..was a HVAC engineer...and I never heard of rads having top mounted inlets or outlets?

 

Doesn't sound like good 'physics' to me..unless you pump it..and force it to do something it doesn't naturally want to do ?

 

I suppose..you could let the hot into the bottom..and the cold out of the top....and then have the bleed valve at the opposite end to the cold outlet..?

Edited by Bobbybass
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I'm puzzled now, not knowing much about plumbing. My two radiators have inlet at the top, outlet at the opposite bottom on two gravity driven loops. Works fine and I don't see how else it could work as the hot pipe (28mm run) is at the top and cold return at the bottom.

 

No pump.

 

I suppose..you could let the hot into the bottom..and the cold out of the top....and then have the bleed valve at the opposite end to the cold outlet..?

 

Why wouldn't the hot water in sink as it cools to come out the bottom?

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I'm puzzled now, not knowing much about plumbing. My two radiators have inlet at the top, outlet at the opposite bottom on two gravity driven loops. Works fine and I don't see how else it could work as the hot pipe (28mm run) is at the top and cold return at the bottom.

 

No pump.

 

 

 

Why wouldn't the hot water in sink as it cools to come out the bottom?

 

Now I'm puzzled..?

You have no pump...?

How does the hot get there in the first place..?

 

If its a natural convection system, I guess what you describe..will work..but how do you get the water...from whatever heats it....without the risk of..whatever heats it..boiling it up as there is no circulation..?

Edited by Bobbybass
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it rises from the back boiler, at first fairly dramatically at 45 degrees then gently to the radiator top. It then returns from the radiator, first rising 8" and then gently downhill to the boiler again.

 

I can see how it would work; heat the water rises to the top which syphons cold from the bottom pipe which pulls the water through the radiator. There is a header tank at the highest point though I've seen them feed to the lower pipe.

 

What I struggle with is how it would work if the hot didn't go into the top of the radiator and out at the bottom.

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it rises from the back boiler, at first fairly dramatically at 45 degrees then gently to the radiator top. It then returns from the radiator, first rising 8" and then gently downhill to the boiler again.

 

I can see how it would work; heat the water rises to the top which syphons cold from the bottom pipe which pulls the water through the radiator. There is a header tank at the highest point though I've seen them feed to the lower pipe.

 

What I struggle with is how it would work if the hot didn't go into the top of the radiator and out at the bottom.

 

That is how a 'natural' central heating system works - hot water flows into the highest point of the radiator and as it cools it finds it's way out at the lowest point. As long as all the pipe work is of appropriate bore and properly arranged to allow a good thermic flow it will work just as well as a modern pumped system.

 

We have had natural (pumpless) systems in two of our houses and on our boat - just as efficient if properly designed and cheaper to run. The Victorians often heated churches and offices in the same way - that is when they weren't using steam!

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