Runtal UF2-72 And 1/2" Wisbro He PEX

Docfletcher

The Runtal input/output is 1/2", so is 1/2" pex the way to go with it's under 2.5gpm flow rate?

Ironman

That depends. What are you connecting it to?

Docfletcher

It will be the 7th zone on my Weil Mclain GV4 Series 2. The loop will be about 70'. It's located at the end of the manifold.

SWEI

Radiator flow rates rarely exceed the capacity of 3/8" PEX. Somebody send a memo to the pipe, valve, and fitting mafia.

Ironman

Are all the loops run in 1/2" pex? The pipes not only need to be of sufficient size to carry enough gpm, but they need to be proportionately sized. If part of the system is converted gravity with 2" pipes and you run a 1/2 line to a rad, guess what? It's not gonna get enough flow.

The other thing you need to watch out for is creating a micro zone. It will short cycle the boiler to death. I would not create a zone with only one rad on it.

Docfletcher

We get old to soon, and smart to late! Well 20 years ago my friend and I put this hot water boiler in, neither of us had ever heard of short cycling . So I ended up with 1650sq ft house and 7 zones only 4 of which are in use now. Each zone a home run, done in 3/4" copper. Currently 2 of the 3 bedrooms have a 12' fin tube rad. The 3rd bedrooms is on the living room zone.
The living room has 45' including the 3rd bedroom of rad. The well insulated family room has 20'. The other 2 baths make up zones 6 & 7.

Usually the living room and family room zones, and of course at least 1 bed room zone are on so that keeps the boiler pretty busy.

So the 6 ft Runtal bath zone 3/4" out of the manifold reduce to 1/2" pex. It's not hooked up yet so I could pull it out and go with a larger pex, but it will still be 1/2" at the rad.

I'd like to keep this boiler another 10 years or more, but if it should crap out I would bring a pro in for the next install. Maybe he could reduce the # of zones effectively.

This was a conversion from hot air to hot water baseboard.

So will my rad get enough flow? Thanks Don

Docfletcher

This bathroom used to be on the loop and part of the master bedroom, controlled by the bedroom thermostat. It was a poor arrangement because the bedroom heat is turned down at night and day making for a cold bathroom. Compounding matters is somewhat high heat loss in the bath because of a large skylight in a high ceiling. There is also a 250CFM exhaust fan. That's why I thought the Runtal with its higher BTU output per foot would be ideal.

Push come shove I suppose I could put the bath back into the bedroom loop.

Ironman

Even if you could get enough btu's from the Runtal, the bathroom will loose heat much faster than the bedroom. That will cause a large temperature swing in the bathroom and unsatisfactory performance.

Putting it on a separate zone would eliminate this, but then you run the possibility of short cycling the boiler.
This scenario comes up every time someone removes an old C.I. rad because "It takes up too much space". The best thing may be simply using some form of electric heat for the bathroom.

Docfletcher

I have a 220V line that used to be use for a dryer. I could run that up to the bath fairly easily since everything is opened up. So it is an option, though as you know it will cost much more to run.

If I put it on the hot water loop will I get enough flow?

SWEI

Do you actually need 250 CFM in the bath? All the time?

The newest generation of variable speed ECM bath fans are pretty slick. Imagine a low speed triggered by an occupancy sensor and a high speed triggered by condensation potential.

Docfletcher

Well we had an awful condensation issue in there and mold. So the fan was put in some years ago. It is mounted in the attic and we use a variable switch to vary the speed. Very quiet. I think it's called continental fan, Canadian if memory serves. I have a flyer on it around here somewhere .

Docfletcher

It's not this one but it looks just like this one.

http://www.build.com/continental-fan-manufacturing-axc150a-es-bathroom-fan/s425695?uid=1764005&source=gg-gba-pla_1764005____49408426759&s_kwcid=PTC!pla!!!78589405404!g!!49408426759!&gclid=CLSxrfO9zsECFSgS7AodfgMAkA

Ironman

You could put the Runtal on with another zone (a downstairs zone that runs the most) and use the electric for supplemental heat. Put it on a timer that you turn on just before you use the bath.

I agree with SWEI that you should keep the fan off except as needed. Getting the bathroom warmer should cause a lot of the moisture and condensation to stop.

SWEI

This might be a good candidate for radiant windows.

Docfletcher

If I put it on the downstairs zone I'd have to get a runtal with 3/4" in an out. Otherwise I'd have a restriction right?

One other idea I'm warming up to... Put both the downstairs and upstairs bathrooms on the same zone. One loop 1/2" he pex . That should moderate or even prevent short cycling.

I still need to know if the 1/2" will give the flow I need. I've seen what SWEI wrote about rads and 3/8th pex but I'm concerned about the manifold effect what with 3/4" on the rest of the manifold and 1/2" zone at the end of the manifold. Photos show the zone valve at the manifold end with 3/4" out and the pex adapter etc.

http://screencast.com/t/yhzGBDQCqKjn

http://screencast.com/t/rhUkzu7R

http://screencast.com/t/m6OMs3Mz

SWEI

I would probably combine the bathrooms as you have suggested (and 1/2" PEX is fine there, but a reverse return would be a good idea.) Then I'd leave out the zone valve for those two. Whenever the boiler fires for any other zone, the bathrooms get heat, which will keep them nice and warm and also help to prevent short cycling.

Docfletcher

SWEI, By a reverse return do you mean make a complete loop? Like this... Two pipe reverse return system. The return piping takes the same basic path as the supply back to the boiler.

Earlier I said 45' of living room radiator, but I should have said 55'

Docfletcher

I get the reverse system now Last in first out. I'll need more pex but that's OK.

Docfletcher

Kinda odd wrapping my head around it, but is this what you mean by reverse return?

Deleted link since it was wrong.

Ironman

No, that's direct return.

Draw a ladder. Connect the supply and return to the legs at the bottom; that's direct return.

Now, disconnect the return from the bottom of the ladder and connect it to the top on the same side it was on. That's reverse return.

Docfletcher

So here is a correct (I Think) reverse return. Please correct me if it's wrong.

http://screencast.com/t/cJiTgxBSWQO

I"m concerned if the zone valve was left out the baths would get to hot.

Ironman

No, that's still direct return. Connecting the outlet of the lower emitter to the top, instead of the right side, does nothing to change it in your drawing. It's still first in, first out. It has to be first in, last out.

I don't know of an easier way to explain it with words than the ladder I described above.

You can try googling "reverse return piping".

Docfletcher

Well, I don't know. I went out online as you suggested and seen a few reverse return piping drawings. This is what I found... Both these are the same drawing just rotated. To me they look like my hand drawing, I don't see the difference.

http://screencast.com/t/8lgec7OE1

http://screencast.com/t/egSEUBORyyY

Ironman

Reverse return = first emitter in, last out. First supplied, last returned. The first emitter is closest to the boiler on the supply, farthest away on the return.
If you'll apply this to your drawing and the others, and trace the flow, I think you'll see the difference.
Your drawing looks similar, but has the first emitter connected closest to the boiler on BOTH the supply and return. That's direct return.

Docfletcher

I take it that the length of pipe to the rad determines the closest to the boiler?

Ironman

No, the connection point.
I think that what you're not seeing is that you would have the same thing in your drawing if you moved the return connection of the lower rad down to where the horizontal line out of the emitter connected to the vertical return line. Effectively, you would have the exact same thing as what you have now: first in and first out. That's direct return. Making it go up and turn the corner(as you have it now) doesn't change the order of connection.

Make the connection points so it's first in, last out and you'll have reverse return. Or, to put it another way: the first emitter has its supply connection closest to the boiler and its return connection farthest away from the boiler.

Docfletcher

http://screencast.com/t/UFkfzfQj

http://screencast.com/t/NEBm9Vc5tT

I derived my drawing from your tutelage and the 2nd drawing from online.

Assume the connection point on the lower rad is closest to the boiler.

Thanks for sticking with me on this. Gezz, I hope it's right.

Here is a better drawing of the one from online...

http://screencast.com/t/FpSstur0

SWEI

I'm a huge fan of reverse return piping, and have seen near-magical results using it on large, complex systems. The easiest way for me to understand it (and still one of the easiest ways to implement it) is a single story structure with radiators around the perimeter. Just run the supply line clockwise and the return line counterclockwise and the whole thing becomes clear.

Ironman

Maybe these drawings will help.
Again: first in, first out = direct return.
First in, last out = reverse return.

Docfletcher

Thanks SWEI, that's a great tip.

Docfletcher

http://screencast.com/t/G3qdVH7UGIH

Only in my case, one rad upstairs and one down.

Ironman

I think you've got it.

Docfletcher

Thanks again for all the help guys.