long pex runs with high head pump?

j boylan

I'm a homeowner putting in a radient system in an existing house as well as an addition(with concrete floors). The supplier I've been talking with about a turnkey/self install radiant system uses long pex runs <500ft with a single high head pump for the 2400sq ft house. I've heard contradicting info on this, most systems tend to use low head pumps with shorter runs <250ft and one pump per zone.
What are opinions of the best way to do it?
I would also appreciate any direct/indirect radiant opinions also.

Thanks much for any help!
JP Boylan
boulder, colorado

S Ebels

You could

Go with what your supplier is recommending if they'll provide a written warranty stating that it will work as designed........ OR........ You could hire a knowledgable heating contractor to design the system for you and coach you through the rough spots.

Dealing locally and having someone with some expertise actually lay an eyeball on your project is an asset that is often vastly underestimated until it's to late!!

CAVEAT EMPTOR!!!

hr

Long loops

work great in shops or large square footage commercial applications. I really see no benefit for a project your size.

Generally homes are set up with 4,5, maybe 6 zones or more. It's one of the biggest features of radiant, the ability to zone all the rooms if desired.

As such, I don't see how 500 foot loops fit into the zoning picture. You don't for instance want half of the living room loop spilling into a bedroom or guest room for example.

High head pumps can be three times the cost of the typical low head pump needed.

Also some of those DIY companies promote open systems which are going to require a bronze or stainless steel high head pump!

I caution you against any combined "open" system by the way.

hot rod

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Mike Kraft_2

Broken rules and big pumps

redesign the wheel.............AGAIN!!!

cheese

Weezbo

HELLO *~/:)

oops my caps were locked; on we go...perhaps you can give us an idea why youd want 500 'loops...i just put a shooting range in and i prefered to use two 276' loops ..to cover the area with a supply and return...the home has 2700+ square foot floor space each space or zone is a different square foot space with different glazing (windows) ceiling heights,floor coverings.knooks and crannies..and useages..you may be certain that the other rooms are equally dispariant..and it is extremely unlikely that they will require 276' supply and return loops..perhaps one room will be three two hundred and fourty seven foot loops...see where this is going? it will all equall out in the long run just wont make it anymore in the real world:( as sad as that is to have to say......you need to get someone to cop a visual or stop by and take a look see...from what you have described so far it sounds just a little bit "Different" as i say. what i mean by that is..it sounds like it wont "Marry up" with any particular stradegy that i have ever heard of or considered or installed.my guess is that you Know something dosent sound right to You and that would be why you have landed on this shore...here we will tell you the truth there isnt any reason not to do so...in order to use 500 foot loops in a modern home the place would look decidedly Weird..i have yet to encounter the home that only needed exactly 500 ' loops...and i plumb many new homes every year.

Bob Murray

You better sound insulate everything because that high head circulator is going to sing, sing, and sing!!

hr

what, exactly, is the reasoning

behind 500 foot loops. The only "angle" I can see is half as many manifold ports compared to 250 foot loops, and, of course, half as much adjust-ability?.

To purposely run 500 foot loops so you HAVE to use a high head pump just doesn't make sense to me.

If you can move exactly the same amount of BTUs with a $55 78 watt pump, why on earth use a $150 200 watt pump?

They use more electricial energy, spin twice the rpm, more prone to cavitate, noise, not always in stock for replacement, don't care to be zone valved, etc. I just don't get it. And if 500 is so great why not 1000 foot loops with a 2 hp pump? Maybe two to three loops per home

hot rod

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ALH_3

Low head

I'd use a smaller pump with zone valves and a differential pressure bypass and keep the runs shorter. Your floors will be a more uniform temperature and your zone valves will have less of a tendency to make noise as they open and close. One can only force a certain amount of fluid through 1/2 inch tubing (and copper distribution lines) before bad things begin to happen. Fluid velocities are important, and should be kept low to avoid cavitation and erosion.

Your method of heat delivery to the living space is also important. It looks as if you'll be putting the tube in concrete for at least part of the installation. If you are planning to heat under any subfloor I would recommend using a heat transfer plate of some sort. The extra convection step some claim to be beneficial is actually very detrimental. The most important things are good tube contact to the transfer plate and good contact between the plate and the subfloor.

There are a million options and there are many different methods. In my opinion there are a lot of irresponsible products out there that make unsubstantiated performance claims. Many of these are sold by well known manufacturers.

If you have to choose, money is best spent upgrading your method of heat delivery as this is the most difficult to change later.

-Andrew

j boylan

The reasoning for the longer loops is less plumbing work because you'll only have switching and manifolds at the boiler rather than a manifold at each room.
The runs are all less than 500', but one or two of them are in the 400's. They use one pump for all the zones and make it a big pump.
It seems that this isn't the popular way to run a radiant system but is there any reason why it cannot work well?
People have mentioned increased noise and perhaps increased power consumption with a larger pump. Are there any other issues?

Thanks again for all the info/feedback

Weezbo

lets recoup right quick....

someone suggested that perhaps you were getting inacurate information and might possibly benifit from hiring someone to at least stop by and look at what you are facing....someone else mentioned what he felt a good stradgey would be with a pressure differential by pass...
Some one else asked what your stradgey might be to require the 500 foot loop runs and larger recirc.another questioned the type of pipe you had chosen and asked whether it was specifically for heating and some where in there i twisted in a word or two about variations in room size ,useage,windows ceilings and wall coverings...
what it seems to me is that you get that maybe some of the lengths just might be different....and that your stradgey is to use these recircs to pump the slab with heat and zone it so that there is some control over the situation...correct?

Glen

The water -

will get dizzy! Seriously though - what flow velocities are anticipated with your proposed system? Any consideration given to heat transfer vs velocity? We design/choose tubing lengths and diameters based on heat transfer needed via a good heat loss calculation. I would view the idea as suspect but if it is supported by a recognized radiant designer then give it a go - caveat emptor. We "fix" lots of systems put in by others - most common complant is that the client is cold - and most times it is due to the wrong pump being installed - generally too much flow for the system.

hr

We really

don't have enough info to really do your design via the www.

First off a heat loss calc needs to be performed to determine exactly how much heat the building will require. A multiplier times the square footage of the home IS NOT a heatloss calc. More and more building departments are requiring a heatloss calc for a permit these days.

This loss calc and design protects you to assure your home will have adequate heat and not get oversized equipment.

Was a heat loss calc and design done for your home? Did the supplier meet with you to go over the design and base a system on your needs? Will they do a site visit to assure everything is installed properly and to code?

I really doubt in a home your size that you would ever need manifolds in every room using 250 foot loops. Possibly one remote manifold. Again no one can make that call without seeing your plans and doing the design.

You really need to keep all the loop lengths within 10% of one another or you will have balance issues and need adjusters on every loop to assure proper flow. This get tricky with high head pumps and may require a PAB valve.

I'd still suggest you involve a local licensed radiant contractor to at least consult with your proposed design and code issues. Plenty in your area. Check the contractor list here or at the RPA website.

Take the time to explore options for the best job.

Open combined radiant/ DHW systems are controversial due the the potential for bacteria groth in un used or un circulated loop over non heating season use. The fluid will sit in these loops at a perfect temperature for breeding baterial growth. Not worth the cost savings, in my opinion, to risk this potential health hazard in your home.

Most licensed plumbers will acknowledge this risk and avoid it.

hot rod

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