New heating zone with runtal radiators

apg12

Hey guys, just found this site while searching for help online, and was hoping for a little advice.

I need to retrofit a new heating zone loop in my basement due to a leak somewhere in the concrete slab. Its a finished basement with a finished floor on top of concrete foundation. The current zone is 3/4 copper and slant/fin baseboard radiators. Due to the construction of the house, I can't simply run new lines to the existing baseboard, so I'm thinking about using high output runtal radiators in locations that are convenient to pipe to using pex. The plan is a little unorthodox, but I'm hoping to make it work. The attached photo is the path that I pretty much need to follow, as I can't run pipes through the main living area without a tremendous amount of work.

I'm far from a plumbing expert, so I guess my questions are... Can I make this work? What is the best way to run the pex?

.

Bob Bona_4

Your plan is to reuse the copper piping in slab to connect the runtals?

apg12

Nope, plan is to run all new pipe using pex. The runtals will be in slightly different locations than then baseboard, as I can't easily get pipe to the current locations.

j a_2

Why are you using Runtals...They are nice but pex adapts to any piping or emitters...What ya got for a boiler ? What ya got for a heat loss? What brand of pex are you using,do not mix brands,,,gets ugly real fast? You do have an installed low water cut off,correct..Boiler in finished basement, raises concerns, do you have enough make up air,50 cubic ft. Per 1 k BTU is a good rule of thumb...but warrants a make up air chart to be filled out...

apg12

I want to use high output radiators so I can hopefully get away with putting them in less than ideal locations. If you look at the pic above, the squiggly lines show where I'd like to put them. I wouldn't be able to get enough btus out of the slant/fins. I'm very open to other suggestions though.

My boiler was just replaced, which was when we realized there was a leak. This is what was installed:

Peerless PF-140 and Amtrol CH-80-Z Hot Water Heater with the following equipment:
Gas Burner
Circulator
Circulator Zone Control Panel
Expansion Tank
Feeder/Backflow Preventer
Electric Shut Off Switch
Air Eliminator
Relief Valve
Isolation Valves
Supply & Return Piping
Centrotherm Venting & Termination Plate

I don't know about heat loss or make up air. As for pex brand, I haven't gotten that far yet. Trying to make a plan before I buy anything, so like I said, I'm very open to suggestions.

j a_2

If that's set up as a direct vent, no worries about make up air...Post a installation picture if you will

apg12

Yes, its a direct vent. Give me a few and I'll get a pic up. I converted to LP and got rid of the old oil burner that crapped out on me.

apg12

This is the best I can get right now. The room is a bit crammed until I get the new laundry room built.

Alan (California Radiant) Forbes

Your sketch shows a series loop piping configuration where the water temperature gets cooler as it gives up some of its heat as it passes through the radiators. You have to size each downstream radiator for a lower water temperature.

It shouldn't be a problem, but you have to pay closer attention to the math. You can pipe it ½" as long as you don't exceed 1,500 BTU's; otherwise you can go to 4,000 BTU's with ¾" pipe and I believe Runtal will provide ¾" radiator tappings.

You also cannot install TRV's at any of the radiators since it will reduce or cut off flow to all the other radiators.

Hard for me to follow the piping, but whoever did it took pride in their workmanship.

Paul Pollets

Runtals are made with 1/2" inlet and outlet. As Alan said, without having a separate supply and returns to each radiator, loop piping can be an issue without doing very careful math. With direct return or reverse return piping, all radiators will get warm at the same time and TRV's can be used. A heat loss should be done to determine the exact BTU rating of the new radiators.

apg12

I made the diagram just to show where the placement of the radiators, and a general path to run the pex. I need to come through the wall separating the garage and living area, under the stairs, then into the bathroom, bedroom and living room.

When I contacted Runtal, they told me that there should be no issue running 3/4 in series and reducing to 1/2" at each radiator as long as I didn't exceed 30k btus or 7 radiators.

I am definitely open to suggestions for a different type of run, but series is all I really know how to do. I had considered trying to use a manifold, but I don't think a 3/4" manifold with 1/2" outlets will cut it.

I'd like to use stock runtals with 1/2" inlets to avoid and special order situations.

Thanks for all the input so far, and Happy New Year!

apg12

The other issue I have is that if I did run it in series, the return would have to follow the same path, as I can not run the pipe through the living room and back to the boiler. Would that make for too much restriction of flow?

Alan (California Radiant) Forbes

Sorry, my figures were off; 15,000 BTU's for ½" and 40,000 BTU's for ¾".

I've never run a ¾" loop reducing to ½" at the radiators. Try it and let us know how it works out.

apg12

I've never done any of this, so I'm really going in blind. A guy at my local plumbing supply suggested using a two pipe system, but I'm not really sure what that is.

Alan (California Radiant) Forbes

The first step to learning is confusion and you should get comfortable with that feeling as you dig deeper.

Here is an article on two types of 2-pipe systems:

file:///Users/Hydro/Downloads/2015Aug_040-045_EngineersNotebook_Duda%20(1).pdf

I've never done a direct return system because it makes sense that on a direct return system, flow would favor the closest radiator and would disfavor the furthest radiator. I just don't want to play around with balancing valves and have always preferred an elegantly engineered system, one that allows physics to balance the heat.

apg12

Thanks for the info. I don't think that article linked properly.

SWEI

Reverse return can be surprisingly easy when the emitters are spread around the building perimeter (assuming there is access from below, of course.)

apg12

Sorry for the lack of knowledge here, but I'm not sure what an emitter is in reference to a reverse return system. This particular heating zone is in the basement on a concrete foundation, so access is extremely limited.

apg12

I've been researching two pipe systems. What about a direct return with TRVs at each radiator?

apg12

Or would there be any benefit to running a complete home run system using a manifold? Would it be worth the additional labor and material?

Zman

apg12 said:

Or would there be any benefit to running a complete home run system using a manifold? Would it be worth the additional labor and material?

Yes, Do it exactly like that.

apg12

What size would the manifold have to be? I only have a 3/4" pipe on the existing zone.

Alan (California Radiant) Forbes

This is when you do your room-by-room heatloss calculations. All will become clear when you have these in hand. It will tell you the sizes of your manifold, supply and return piping and radiators (also called emitters).

Work this out here:
http://www.slantfin.com/slantfin-heat-loss-calculator/
and then get back to us.

apg12

Based on the heat loss calculator, I need a total of 16639 btus. 12033 for the living area, 4078 for the bedroom, and 528 for the bath.

Alan (California Radiant) Forbes

Nice! That tells you that a ¾" supply and return to the manifold is fine and that a ½" supply and return to each radiator will work. It also tells you how large your radiators will be. Runtal has sizing charts for different water temperatures.

apg12

Great, thanks for the info! My boiler is set at 170 so I'll size the radiators based on that.

Any recommendations on pex brands and fittings? I believe oxygen barrier pex is the appropriate type? I was thinking about crimps since the tools are affordable for a DIYer. I'm potentially going to buy everything from supplyhouse.com.

There are so many different options for manifolds, so what do I need to look for?

apg12

Would it be possible to put the manifold in either the closet or crawlspace under the stairs and run the supply/return there as opposed to putting the manifold in the boiler room and having the longer 1/2" to each radiator? But if I did that, I don't know how I would connect the one radiator on the boiler room wall.

Zman

You would get better efficiency from you boiler if you can lower your water temps.

apg12

That's what my installer set it at, and I think I'll need the higher temp to get the btus I need out of the runtals.

Zman

It all comes down to how you size the Runtals. Are you only heating with Runtals? There is a deration formula for sizing them for lower, more efficient temps.

apg12

Yea I'm using just the runtals. In the living room area, I need to get to 12k btus with just two radiators. I'm looking at using the 3-4' UF-6 or UF-8 panels.

Zman

I would do a room to room heat loss then size the runtals to those numbers. I would suggest sizing to 140 or less for the design day.
You would then set your condensing boiler on an outdoor reset curve and get the efficiency it was designed for.
Right now you are getting no more than 88% out of your high efficiency boiler.

apg12

I did the heat loss calculations. The results are posted above. There is an outdoor reset installed on the boiler.

Zman

Great, Choose the efficiency you want and size the rads accordingly..

apg12

Thanks for the input.

Bump for pex and manifold recommendations. 3/4 Manifolds don't seem to be very common.

Bob Bona_4

I'd do a manifold system as well, with 1/2" piping to the rads. My only hesitancy here is not seeing the site to anticipate possible routes or problems. I'd use a composite pex product like Viega Fostapex or Uponor Multicor. Your manifolds should be a manufactured set, with balance valves built in. The in/out of the manifolds are handled with adaptors to the required supply/return pipe size. You'd use the brand manifold of the brand pex you choose. Easier for fitting compatibility.

Zman

The manifolds themselves will likely be 1" with 1/2" ports. This helps them distribute more evenly. The idea is to get the flow in the manifold in the 2 fps range. It is perfectly normal to feed a 1" manifold with a 3/4" pipe as pex distribution piping can handle easily handle up to 4-6 fps.

apg12

Supplyhouse.com has several options for a manufactured manifold system, I just wasn't seeing anything with a 3/4 feed. What would be the appropriate fitting to go from 3/4 pex to 1" manifold?

Also, what is the benefit of using pex-al-pex? There seems to be a pretty big price difference between that and the oxygen barrier pex-a I had planned on using.

psb75

Why don't you get a standardized 4-5 port (one extra port) 1/2" x 1" Uponor manifold set and pipe your 4-5 panel radiators w/ a normal home-run set-up using 1/2" oxy-barrier pex pipe? Skip the 3/4" pipe altogether? No need for pex-al-pex.

Bob Bona_4

I wouldn't use anything but PAP in a high temp heating application. Too much movement with reg pex in heating cycles. Squeaks/chafing/major pipe movement. There's a reason for that price difference. Better product.

Get the manifold adapter close to 3/4 and reduce as necessary.

apg12

psb75 said:

Why don't you get a standardized 4-5 port (one extra port) 1/2" x 1" Uponor manifold set and pipe your 4-5 panel radiators w/ a normal home-run set-up using 1/2" oxy-barrier pex pipe? Skip the 3/4" pipe altogether? No need for pex-al-pex.

I have 3/4 copper coming out of the circulator now, so I would run that directly to the manifold, no?