Max lenght of runs question
Last Post 22 Apr 2015 04:32 PM by sailawayrb. 4 Replies.
Printer Friendly
Sort:
PrevPrev NextNext
You are not authorized to post a reply.
Author Messages
wingam00User is Offline
New Member
New Member
Send Private Message
Posts:2

--
22 Apr 2015 10:27 AM
Using 1/2 pex, from what I have found the max run for 1/2  pex in a radiant heat system should be no more than 300 feet, 250 is better.  My question is does this include the distance to the manifold/pump/adjustment values or just what is in the slab?

Thank you
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
22 Apr 2015 10:35 AM
The 300' max length for 1/2 PEX is generally taken as the total length to/from the manifold. However, what actually limits the length is the hydraulic friction generated within the PEX given the flow rate that is required to generate the heat gain that is required to replace the room/zone heat loss. The pump needs to be able to supply sufficient head to overcome this hydraulic friction head loss at this required flow rate. The head loss of the distribution line(s) to the manifold(s) should also be considered, but this is typically negligible.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
jonrUser is Offline
Senior Member
Senior Member
Send Private Message
Posts:5341

--
22 Apr 2015 11:50 AM
Also consider variation in heat delivery throughout the loop. While there might be enough heat delivered at a reasonable pumping cost, some parts of the floor could be objectionably cooler.
wingam00User is Offline
New Member
New Member
Send Private Message
Posts:2

--
22 Apr 2015 12:19 PM
The pex that is running to the section that is too transfer the heat, I will insulate to help keep get the heat to the needed parts.

 Does this sound like a good idea and worth doing?
sailawayrbUser is Offline
Veteran Member
Veteran Member
Send Private Message
Posts:2270
Avatar

--
22 Apr 2015 04:32 PM
Yes, it usually best to have the heat gain where you actually want it and not have heat gain where you really don’t want it. However, there are always some exceptions and good judgement needs to be applied. For example, we have a utility room in our place where the boiler and all the other hydronic radiant components reside. This room is on the northwest corner of our building (i.e., coldest corner of house) and is not specifically heated except for some small uninsulated sections of distribution line and associated allowed heat loss. However, all the majority of distribution lines to the manifolds are insulated. Since these line pass through a wall that is shared with a kitchen pantry (which is also not specifically heated to reduce the potential of food spoilage), we would not want to create a radiant section of wall here either.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
You are not authorized to post a reply.

Active Forums 4.1
Membership Membership: Latest New User Latest: hudson2000 New Today New Today: 0 New Yesterday New Yesterday: 2 User Count Overall: 34707
People Online People Online: Visitors Visitors: 80 Members Members: 0 Total Total: 80
Copyright 2011 by BuildCentral, Inc.   Terms Of Use  Privacy Statement