add radiant zone to home run system

kev

I have a single zone mod/con system with 1/2" pex home runs from cast iron rads to radiant manifolds at boiler. The radiator in bathroom is being removed and a lightweight pour is going over 1/2'' pex in floor. I am trying to connect the tubing that is already at the bathroom and the boiler room to my system, I do need to run lower temps to my floor so mixing is a must while also keeping this as simple as possible. Ideally  this would operate at the same time as my main zone so not to include any thermostat or pumps. Is there a way to use my existing system pump and take offs from the manifolds to move water through a mixing valve without running an extra pump? Boiler is set up primary secondary so two pumps are always running.

Paul Pollets

An easier way

Try the Oventrop UniBox. It is designed to take high temps and make a radiant mix temp without additional piping, mixing valve or pump.  Simply connect the radiator supply and return to the RFH zone and pipe the return through the UniBox, per instructions.  There is no easier or less expensive method to install a RFH zone where radiators are the prime heat emitter.

NRT_Rob

?

the unibox is a mixing device?



I thought it modulated flow only?

CMadatMe

Absolutely Not

There is no way. You must treat this as an additional zone. Like you said. You  understand that you have to mix the water temp down. Once you mix you have to have some way to get the water after the mix through the floor. Best bet is just add the additional zone. Who's mod/con? Does this boiler have the ability to run a second heating curve with a modulating mixing valve or injection pump? Why do you not want to run an extra zone? Is your budget an issue?

Big Ed_4

Just a Thought

Why not add just add a floor sensor and zone valve .. Wouldn't the floor sensor control the correct floor temperature for the load?

hot_rod

or a suspended tube application

like Ultra Fin. this method suspends the tube below the subflor and used the higher temperature without actually touching the tube to the floor. it's not a bad way to go for a small area retrofit. if you can get below the space, of course..



hr

kev

the work

is taking place above the floor , so staple up is not and option. Boiler is a GB 142 and two pumps are running now basically constantly. I just posted to see if there was a way to utilize the home runs that are existing and also keep it simple. This bath is 10'x7' so the load is very small. Thanks for the response.

MikeT_Swampeast_MO

Electric?

For such a small area have you considered an in-floor, electric system?  While most of the systems will say "Only for floor warming--NOT heating" they can and do work for heating.  You just have to be certain that you calculate your heat loss and ensure that the uncovered floor area can provide sufficient heat at a reasonable floor temp.  Do though--I know this from experiencing one (not one I installed) that did not have--use a controller that senses floor temperature!



I have done exactly what you asked in my own home by adding heated bathroom floors that run off of a two pipe constantly circulating system with cast iron rads and no form of control or additional valves/circulators for the baths.  Perhaps I just got lucky, but I studied the system incredibly before installation (including innumerable temperature measurements) and genuinely obsessed over the various methods I used to get the heat into the floor that include copper in Thermofin (under floor), copper slipped through garden hose for "insulation" (in a huge mud slab shower) and PEX surrounded by carefully cut cement board that looks similar to Warmboard without the aluminum.  All were extremely labor intensive and work flawlessly.  The only problem happened after I installed a mod-con.  When adjusted to a "starvation" heating curve that barely provides enough heat to maintain temperature settings (about 65F in occupied space), the bath floors are no longer truly warm to the bare foot--they are neutral and while comfortable and still 2-3F above the temp of the surrounding rooms you don't get a "this is a 'hot' room" feeling of the big bath with electric floor or with the boiler controls adjusted for a less energy efficient heating curve.

kev

Just throwing it at the wall

and hoping there was some sure fire quick and easy way to accomplish this.Looks like I will use the existing home runs and put the pex in the mud with a sensor and mix and pump at the boiler. Maybe first try having the pump only operate when the system pumps run. Thanks again.