Infloor radiant /mixing valve clarification


Old 02-16-06, 12:10 PM
Visiting Guest
Posts: n/a
Infloor radiant /mixing valve clarification

I don't totally understand how they work.

What I do understand ... in an infloor system they introduce warm water into the system ( circ pump and loop) to meet the temperature set for that system
( designed temperature of the floor )

This is controlled by ... what ? a T-stat or a special controller... ? Both ?

Next question ( the dumb question) where does the extra water go? Does it continue on in the supply ( feed ) or does it go into the return manifold?

Are there any basic diagrams laying around the Net some where?

This is hydronic electric with rads and I am thinking of adding a couple infloor loops in a slab and am just trying to visualize how much I may have to change my existing header and returns (1 1/4" with 3/4" supplies )

Thanks in advance
Sponsored Links
Old 02-16-06, 12:52 PM
Who's Avatar
Who is offline
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
Pretty tough questions to answer given the multitude of answers.

The difficult part is figuring out what temps your various heat circuits need and what the minimum return temperature is for your boiler. If you have a condensing boiler, you want to bring the water back as cool as possible. If it is a gas fired cast iron boiler then you'll need return temps of 140 minimum. With that out of the way, you want your highest temp circuits served first and your lowest temp circuits served last. They can all tee out at the beginning and all teel back together at the end or you can tee out a lower temp circuit after other circuits have dropped the temps and then tee it back afterwards.

As for how to control the temps of the branches it can range from vey simple to very complex. You could manually valve a circuit so that part of the circuit just recirculates water in that branch and just gradually mixes in a small fraction of the heated water. You can put a 3-way temperature controlled mixing valve on and set it to maintain a certain temp (these are non-electric). You can go whole hog and get a mixing block that uses an outdoor sensor to determine what water temperature you need for a circuit and have it control an injection pump as well as having a wall t-stat and an infloor sensor to kep the rrom temp steady. There are many many ways. There are many trade-offs as well so the method used will be a function of the requirements. If it's all in-floor and a condensing boiler, there is no need to mix down.

Usually an extra circulator and a 3-way valve are used. The key thing with in-floor is to keep the floor from becoming uncomfortable warm (+85 or so).

Here are bunch of methods all on one page.
Old 02-16-06, 12:58 PM
Join Date: Feb 2005
Location: New England
Posts: 75
Received 0 Votes on 0 Posts
Radiant Mixing Valves

Mixing valves used for radiant have three (sometimes four) ports; basically, one port accepts the hot water directly from the boiler supply, the second port accepts cold water from the returning loop, just before it goes back into the boiler, & the 3rd port COMBINES the hot & cold to produce water at ~100 degrees to supply the in-floor radiant loop.

Some 3-way valves control water temp by manual setting, others by thermostatic means; the room temp can be controlled by thermostat, by a setpoint thermostatic control attached to the supply pipes, or an outdoor reset control.

Adding loops to your radiant system would involve design & heat-loss calculations that you would have to learn, or let a pro do it.

Diagrams can be found by Googling the articles by John Siegenthaler below (using the quotes); his book is in most libraries, "Modern Hydronic Heating" & has most of the info you need in Chapter 10.

"A little floor warming please", "Dashed Expectations", "Less is more", "The do's and don'ts of three-way thermostatic valves"
Old 02-16-06, 04:35 PM
Visiting Guest
Posts: n/a
That explains a lot.

Of course there is always more details....

Quote "you would have to learn, or let a pro do it."

That is very sage advice and I have been trying. Over 6 months of about 6 or 7 calls to different guys and I have only been able to get one qoute though I have now ( since I posted this ) have two more guys coming to look at it.

This is the project and of course it is underway.

There is pex in the slab for the addition that I put in. I bought it from a guy that backed out of the job (inexperience in radiant) and I think he had a heatloss done for that room and I want to suppliment the heat in the sunroom or the enclosed porch with some infloor heat.

The original installation was done by a first timer in 89' though he was a licenced plumber and heating guy. He had some consulation with a good supplier but there are some weak spots in the system.

Whether its a condensing boiler I don't have a clue. I am sure you smart guys can tell me

I have designed and built 2 single story houses on slabs where we put infloor in and of course I want it. This is my own house. The one qoute I did receive was almost 7k I have not seen the paper on it so I am trying to understand what the parts may be.

I have reached a point were I have to rework the rads and supply lines upstairs inorder to continue the drywall etc downstairs.

You have given me a start so I can look and see what kind of space these controls may need.

Any suggesttions would apperciated. I know this looks like a hodge podge system but it does managed to work.

Many thanks. It has helped
Old 02-17-06, 06:50 AM
Who's Avatar
Who is offline
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
Was the PEX pressure tested and does it have an oxygen barrier layer?

What does your boiler burn?
Old 02-17-06, 08:04 AM
Visiting Guest
Posts: n/a

Yes it has a barrier. No it was not pressure tested. I am aware about pressure testing as I have done infloor on a couple of slab houses and we pressurized them before the concrete clowns poured. This was not pressurized BUT I did the pour myself straight from the truck ( no wheelbarrows) so I am confident about the installation.

There are 2 boilers in that picture. The one on the wall is a 25kw electric boiler. The other black thingy is woodfired boiler known as the Furnace Works made in Minnisota in the early 80's.

I run the system with aquastat on the electric boiler set fairly low ( 100 - 140 deg) depending on the outside temps. The high end of the wood aquastat is set to close the automatic damper @ 190. When the woodboiler can't supply enough heat the elec takes over.

There are three loops. The upstairs is on its own zone control and T-stat. There other two loops ( mainfloor, mainfloor and partial basement) are free flow but the lower T-stat shuts off the wood damper when at temperature.

I am sure there are lots of suggestions for replumbing the headers but it was configured to isolate the woodboiler,circ pump and to freeflow in the advent of frequent rural power failures.

Some of the system made sense when it was installed but really could be changed. The circ pump is between the Elec and the wood boilers maybe not the best but it does make sure the water is circulating through elec boiler when it kicks in ( it has 5 elements in it).

The thing that should be changed is where the 1 1/4" leaves the woodboiler. It 90's straight off the top. This builds up heat quickly when the power fails and there is a good fire going. I saw somewhere a recommondation to setup a n emergency loop whit an electric gate valve tha opened when the power failed. It also should go straight into the bottom of the electric boiler but I am also dealing space factors and lots of residual heat off the woodboiler. I am wary of moving the circ pump ( hidden in lower left of picture) any closer to the woodboiler as it not double walled at the back.

Thanks for the Honeywell link it answered a lot of my questions and it looks liek the mechanical injection would be the best avenue to persue. Planning where it enters into the system is the next mystery.
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: