replacing mains with PEX

Bob Bona_4

TXV's anyways, and like Mark said, you can zone off the home runs to the 2nd floor rads w/ motorized or thermal loop actuators if the entire house is on one manifold set. For total of 8 rads, that is possible. You'll need to put the actuators on ALL loops in this case in order to seperate which loops are to be zoned.

Greg_51

replacing mains with PEX

Last year the 60-year-old boiler for my house's gravity hot water system failed and was replaced.

This summer I want to start finishing my basement, which requires that I move my mains up into the joists. My first choice would be to replace them with PEX.

My main question is, can I do this and how do I figure out what size PEX to use? The original mains have about a 2" outside diameter, but my new boiler has a circulator, which the original system did not. I expect I don't need such large pipes for my mains now that the system is no longer driven by gravity. In fact the piping near the new boiler is 1" copper which is adapted to those big old iron mains.

What are the possible pitfalls of this project?

To complicate things, I'm hoping to install radiant floor heat in two new basement rooms (a rec room and a bathroom), which will place new demands on the system that currently do not exist.

My house is a 1.5 story bungalow with two bedrooms down and one large (bed)room up. It's 1200 finished square feet, and the boiler services 8 radiators, 6 on the main floor and 2 on the 2nd floor.

Originally one outlet/inlet from my boiler fed 5 radiators and the other fed 3. With the new boiler those were combined.

I'd really appreciate some advice. I have a helper with enough plumbing experience to get me through rough patches, but I want to get the fundamentals right and I do not want to screw up my system.

And I certainly have no wish to get rid of my radiators.

Thanks!

Justin Gavin_5

Using Pex

Couple of things,

Instead of Pex use Pex Aluminum Pex such as Viega Fosta Pex or Wirsbo Alumapex. Reason being is expansion. Regular Pex will expand and make a ton of noise in your joists.

What you need to do is have a heat loss done room by room.

Add the totals per zone.

So if the first zone is lets say 40,000 Btu's and the second zone is 30,000 btus you can then use a simple equation.

BTU's Required divided by the Delta T (usually 20) x 500.

For example if the first zone required 40,000 you would divide 40,000 by 10,000 (20 x 500) and get 4 GPM. You can move 4 GPM's through 3/4" copper or aluminum pex any more than that you must go to 1" which will cover you up to 80,000 btus. Any more than that and you have to go up to 1.25". Now you have to figure out the pressure drop of the longest run to ensure that the new boiler's circulator is going to be strong enough to push the water through. In most cases depending on the piping arrangments you should be OK.

I hope this helps.

Good Luck,

Justin

Bob Bona_4

consider

a manifold setup with 1/2" PAP going to each radiator (supply and return). Unless you have a HUGE radiator (15K BTU+) , and in a cape that would be unlikely, 1/2" would be fine. Figure new rad valves to adapt, thermostatic radiator valves would be best. The new boiler can be piped for constant circulation via outdoor reset, or regular on/off.

Mains to manifolds would be sized to house total BTU requirement. Manifold can be right in the boiler area.

Lay out what you have. Do heat loss. Do EDR conversion to BTU output of your rads to confirm 1/2" will do.

Many a cape like yours I have done- radiant, panel rad, CI rad.

Greg_51

replacing mains with PEX

Thanks - I was at a sticking point and these suggestions are very helpful.

I forgot to mention that I'd like for the upper level to have its own thermostat. I reckon a manifold setup is the best way of making this possible. If I have two zones, is it safe to assume that one zone being off will mean those runs are closed off, or should I plan to put thermostatic valves on all my radiators?

Will do the math later and post a layout.

Thanks again, especially for being patient with a total amateur.

Mark Custis

You can

get manifolds with motorized actuators.

Mark Custis

Bob

I want to do a job like that. Bundle the actuators into zones like Arzel does with their forced air systems.

Greg_51

specs

Using the advice at http://www.colonialsupply.com/resources/radiator3.htm I have estimates for my radiators.

The ones on the ground floor are old and based on column/height/section specs the BTU/h for the five of them are about 12000, 9000, 9000, 4000, 9000, and 8000, totaling 53000 BTU/h translating to 5.3 gpm for that zone.

The second floor radiators are newer (and one of them is large, with 5 tubes and 35 sections) and I estimate those emit 9000 and 18000 BTU/h, so that part of the house gets 27000 BTU/h translating to 2.7 gpm.

All for a total of about 80000 BTU/h.

Before it's all done I'll try to get more exact information for these radiators, but judging from the things I'm reading, those numbers seem reasonable.

As for confirming the capability of my circulator: the most distant radiator on the main floor is about 40' from the circulator. The most distant one on the second floor is 35' from the circulator horizontally plus about 10' above the mains. Still need to figure out what this translates to.

I wonder now if it makes sense to have separate manifolds for the two zones, though the one for the 2nd floor would only feed two radiators.

Question: The 2nd floor zone, which needs 2.7 or let's just say 3 gpm, calls for 3/4" pipe to that manifold (assuming I use a separate manifold for each zone). Would it place additional stress on the circulator if that pipe were larger than necessary, say 1"? I'm imagining that someday someone (possibly me) might expand the second floor with dormers, etc., which would likely lead to new heating units and possibly the need for a higher flow rate to that zone's manifold. I thought I could use a manifold with four outlets and leave two of them unused.