Design idea using slant fin on system made for radiators, from self-destructive DIYer

NYMartin

First, thanks for all replies, lengthy though this may be, I promise to keep it interesting.
I'm that guy who knows just enough physics to come up with strange DIY fixes that sometimes turn into story-worthy catastrophes. I have an old two story house with a hot water radiator system. I have added two small bathrooms, one on the first floor, one in the basement right below it. My brain has latched onto a heating idea which might cause you to cough up your cereal. But I like it, so tell me if I'm about to do something clever, or cause the end of civilization as we know it.

There are supply and return pipes running the length of the basement. At the end of one, I'm thinking of adding a run to the new basement bathroom, about a 7 foot drop. It would connect to a 3-foot slant fin baseboard. From there it would rise up the wall and through the floor to the new first floor bathroom, about an 8 foot rise. It would connect to a 4-foot slant fin run there, which would return back through the floor into the basement bathroom. The return leg will run along the top of the basement bathroom wall and connect to the main supply, a slight drop. My thinking is that since the final return leg will still have hot water, I should make it also slant fin, even though it will high up on the wall of the basement bathroom. And, since there is no danger of kicking it, it would be exposed for maximum output. So the basement bathroom will be warmed by the baseboard run, and whatever heat gets recaptured off that return leg would be purely bonus. Yes, weird looking, but a bathroom that feels like Florida would be worth it, no?

My first concern is that having a heater below the basement supply/return pipes would necessitate putting a valve on the basement slant fin run. Second, is the natural force/pressure enough to keep it flowing through the dip below the loop level, or will I need some kind of backflow preventer? Third, is there a substantial pressure difference between a system designed for cast iron radiators and a slant fin system, and should I be worried about it? Lastly, will this kind of freaky arrangement cause a disturbance in The Force, as if millions of voices cried out and were suddenly silenced?

Once again, thanks again for all input, and all the good advice which I have a bad history if ignoring.

JohnNY

The final fin-tube would only "recapture" heat if the water running through it were cooler than the air in that bathroom.

Temperature seeks an equilibrium.

Does my answer seem like I'm reading your post right?

vvzz

I'm not doing this professionally, but here is my 2c: before you even start doing anything, do a heat loss calculation to see exactly how much heat each bathroom needs. This way you are operating with concrete numbers.

JohnNY

He's not looking for that level of precision. He's playing with hydronics, just like I do in my brother's and parents' homes.

bmwpowere36m3

Without doing heat loss, head loss, gpm requirements, etc... It's just a mental masturbation exercise.

Just install it and see what happens...

NYMartin

well, I'm ok with masturbation. To the first johnNY comment, my theory is that the water passing through the upstairs slant fin would lose some heat, but still be hot on its way through the return leg. So I would want to use those therms to further heat the basement bathroom as the water returns to boiler heaven.

It occurred to me after I posted that if there is enough pressure to force the water to a 2nd floor, it would be more than enough to push it from the basement floor to the 1st floor.

bob_46

Does your existing system have a pump ?

Paul48

You're just making a series loop. It's no different than if you ran your supply to a 3rd bathroom. The key is to put enough heat where it is needed, and you need a heat loss calculation to determine that.

NYMartin

I believe there is a small pump attached to the boiler.
The endpoint its attaching to used to go to a cast iron radiator in the kitchen. I took it out and there was no change in comfort level. Because the addition will create a loop where now there are two stubs, I suspect it will make the system slightly more efficient. Offsetting that, the total length of the new run will be about 36 feet of (relatively) straight pipe. I don't think the net loss from the overall system will be significant.

Brewbeer

Is this a monoflow system?

NYMartin

No, there is a separate return pipe. The radiators are parallel circuits on it.

Brewbeer

Is this a direct return or reverse return system? I'm trying to understand how the "two stubs" relate to the rest of the piping system.

Why not put the basement radiator down by the floor? It will do a better job warming the space if it is at floor level. If you want a Florida effect, try an oversized panel radiator.

bob_46

Is your system gravity or is it pumped ?

NYMartin

There will be a baseboard run in the basement bathroom, which will continue on to the bathroom above it, which will also have a baseboard run (in series, as was commented above). When that returns, it comes back down through the basement bathroom. So my feeling was that this return leg, which would be high up on the basement wall, could be slant fin pipe, too. So it's not either a high run or a low run, but actually both, for full-on Florida.

I believe the system is largely gravity but there is a small pump attached to the boiler. My belief is that the heat pressure and marginal impelling force will be more than enough to create constant flow in the new circuit.

Paul48

There are free Heat Loss programs available online. Slant/Fin has one available. It will tell you how much heat is required for each room, at design day temperature. Every emitter has a rated output at a given supply temperature. Then it is just a matter of sizing your emitters to whatever temperature you like. There is no guesswork involved.

NYMartin

thanks for that ^

vvzz

Another good option is HeatCad (there's a free one month trial)