Adding radiators using Pex piping

Rob_14

I want to add some radiators to my top floor rooms. (I guess it was an attic that someone added rooms to at some point). I have an old 60-80 year old home with hot water heat. We have the big 1-1/2 to 2" iron mains in the basement that branch off to the radiators. All work as one zone (without the zone valve) with a circulator. My thought was to seperate the existing radiators into one zone and add another zone (using zone valves). I want to add the new zone with Pex piping so it will be easier to thread the piping through the existing walls to the top floor with the least amount of demolition.

I only need three radiators up there.

Questions:
1. I need help to determine what size Pex tubing to use. -How is that determined? -By heat loss calc, size of radiators, etc.?
2. Does it matter how I tee in the lines? In other words, how do I make sure the water doesn't just circulate through the closest radiator. Is that just a matter of throttling down one radiator so more water flows to the other radiators?
3. Do I need to do a manifold in the basement and run a seperate pipe to each radiator or can I run a feed and return only to the second floor and branch off there or does it even matter? I guess I thought if I did it in the basement I could do a manifold system with balaning valves there so I could be sure each radiator got enough the same amount of heat. Is that over kill and just adjusting the radiator valve will do the same thing??
4. Wiring is a whole another can or worms bu I'll "burn that bridge" when I get to that point.

Thanks for your help.

Joe Mattiello

The size of the tubing is dictated by the flow rate required. You will have to calculate the btu output of the radiators. Rule of thumb, is One gpm, per 10,000 btu. Maximum, flow rate through 3/4" tubing is 6gpm, which can handle 60,000 btu.

Tom Meyer

6 gpm?

We use 4gpm (max) for 3/4" PEX. I'd love to use 6gpm if we could find the support documentation for it.


Tom Meyer
Senior Designer/Trainer
Precision Hydronics Corp
www.precisionhydronics.com

hr

the heat transport rate

will be determined by the delta T you design around. Don't necessarly build around 20° delta's.

3/4" pex running a 30° delta T could move 60,000 BTU at a 3.6 fps

80,000 at 35 delta T at 4.2 fps 4.7 gpm flow.

Radiators could handle a 30 -35 delta T, usually. Europeans like to build around 40° delta t on some panel radiator applications. Often this will put you in 1/2 or 5/8" pex.

Play with some numbers, it's fun.

hot rod

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mark_29

> I want to add some radiators to my top floor

> rooms. (I guess it was an attic that someone

> added rooms to at some point). I have an old

> 60-80 year old home with hot water heat. We have

> the big 1-1/2 to 2" iron mains in the basement

> that branch off to the radiators. All work as one

> zone (without the zone valve) with a circulator.

> My thought was to seperate the existing radiators

> into one zone and add another zone (using zone

> valves). I want to add the new zone with Pex

> piping so it will be easier to thread the piping

> through the existing walls to the top floor with

> the least amount of demolition.

>

> I only need

> three radiators up there.

>

> Questions: 1. I

> need help to determine what size Pex tubing to

> use. -How is that determined? -By heat loss calc,

> size of radiators, etc.? 2. Does it matter how

> I tee in the lines? In other words, how do I make

> sure the water doesn't just circulate through the

> closest radiator. Is that just a matter of

> throttling down one radiator so more water flows

> to the other radiators? 3. Do I need to do a

> manifold in the basement and run a seperate pipe

> to each radiator or can I run a feed and return

> only to the second floor and branch off there or

> does it even matter? I guess I thought if I did

> it in the basement I could do a manifold system

> with balaning valves there so I could be sure

> each radiator got enough the same amount of heat.

> Is that over kill and just adjusting the radiator

> valve will do the same thing?? 4. Wiring is a

> whole another can or worms bu I'll "burn that

> bridge" when I get to that point.

>

> Thanks for

> your help.

Tom Meyer

Yup. I got trapped into the \"Delta 20\" mindset

Thanks for reminding me, Hot Rod. How soon we forget the sources of the Rules of Thumb.

Tom Meyer
Senior Designer/Trainer
Precision Hydronics Corp
www.precisionhydronics.com