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Radiant heat manifolds

I am building a log cabin and plan on installing radiant heat. I have been reading where most recommend that the circuits do not exceed 300 ft for ½ inch PEX. The problem is that the house is a long ranch (64 ft.) and for the 1st 4-5 circuits and you eat up any where from 125-150 feet just getting to and from the mechanical room. Some sites talk of a remote (or forward manifold) or even a “long” manifold very simply my question is: "Wouldn’t the PEX between the forward manifold or the long manifold and mechanical room become part of each circuit coming off of that manifold anyway? Therefore in effect you really would not be shortening any circuit. Or is the fact that you would use 3/4 pex or copper for the manifold create more volume and so less heat loss and the length in the manifold would not be a factor for the circuit lengths. Did that make sense??:confused:

Re: Radiant heat manifolds

One common method is to set up a CENTRALLY LOCATED 5-circuit or 10-circuit MANIFOLD STATION in the geographical middle location of the house floor plan.

This is usually located at the base of 16" oc wall studs so easy access can be obtained.

All the 1/2" PEX supply & return tubes are routed to this main supply/return MANIFOLD STATION--no tubing run is allowed to exceed 300'.

Then, a 1" to 1 1/2" supply & return pipe is routed to the boiler room to supply the hot water volume needed for the whole system.

Some boilers are sensitive to cold return supply water & must be protected from damage with a bypass loop and/or radiant injection secondary loops.

Google radiant floor heat "manifold station" (quotes around only "manifold station") for more info & representative diagrams.

John Siegenthaler in his book "Modern Hydronic Heating" has piping diagrams & manifold arrangements---the book is free of charge at local libraries.


Re: Radiant heat manifolds

Thanks for your quick reply and the link. :o I feel stupid saying this but in reading your reply it would seem that the pipping to and from the manifolds would not be considered in creating the 300' circuits. In other words if you have 284'of 1/2 PEXa in a circuit the fact that you have 50' of copper pipe to and from the manifolds does not make that ciruit 384'. I'll be going to pick up the book this evening. Oh by the way I'm using a condensing boiler so I should not need a by-pass loop.

Thanks again

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