DIY Chatroom Home Improvement Forum

DIY Chatroom Home Improvement Forum (
-   HVAC (
-   -   Radiant floor heating questions (

secutanudu 02-27-2010 02:36 PM

Radiant floor heating questions
I want to put in radiant floor heating in my bathroom and have some questions. Currently, I have:

Mono-flow hot water system with cast iron radiators on the first floor, baseboards on the second floor. I keep this boiler at about 170 degrees. I also have an electric water heater for my drinking water. Not the best system, but it's what I have.

What is the best way for me to get hot-water based radiant floor heating in my bathroom floor? I want to put this floor heating on the main bathroom floor as well as inside my new custom shower (tile floor) Can I use electric in-floor heating coils inside a shower?

Assuming I will be doing hydronic, what are my options?

If I use my boiler, I understand i need a tempering valve to bring the temp down to about 120. How do these work? They introduce cold water to the zone? How can water be added to a closed heating system, does it drain somewhere too?

Can I run this heating zone off my water heater? I keep it at about 110-120 anyway. Is it legal to run a loop fro my hot water heater, through some pex in the floor, then back into the heater?

Any other advice?


warmsmeallup 02-27-2010 04:51 PM


Originally Posted by secutanudu (Post 406882)
Can I use electric in-floor heating coils inside a shower?

Only low voltage can be used in the shower. It's a waterproof element and ...low voltage.

beenthere 02-27-2010 05:03 PM

Many water heaters aren't rated as a comfort heating appliance.

secutanudu 02-27-2010 07:13 PM


Originally Posted by warmsmeallup (Post 406938)
Only low voltage can be used in the shower. It's a waterproof element and ...low voltage.

How effective is it?

warmsmeallup 02-27-2010 09:45 PM

Effective? I think you want to know if it will warm the floor or seat in the shower... yes, definitely. It can also be designed to be used as primary heat given a well insulated space. A heat loss calc would need to be performed for primary heating though.

secutanudu 02-28-2010 06:27 AM

Ok. thanks. So I can use non-low voltage for the general floor, and low voltage for the shower floor?

If I decide to go with hot water off my boiler - i need a tempering valve? Any idea how those work?

warmsmeallup 02-28-2010 09:51 AM

No, if you use hydronics, you get those answers from a plumber. We don't do any hydronics at all.

If you use electric and the shower is a must, then you use a low voltage system throughout. If you don't do the shower, you could use either low or line voltage.

The differences between the two:
Line voltage feeds 120v or 240v directly into the element.
Low voltage feeds the line voltage to a transformer which then sends a lower voltage (6 to 30 volts) to the element in the floor.
Line voltage has a 10 year element warranty
Low voltage has a 25 year warranty
Low voltage can be cut in the field and line voltage must be used in the length you buy. You can not cut line voltage elements.
Low voltage costs a little more for materials because of the transformer included.

beenthere 02-28-2010 12:57 PM


Originally Posted by secutanudu (Post 407147)

If I decide to go with hot water off my boiler - i need a tempering valve? Any idea how those work?

Very good.

They mix the hot water from the boiler with the cooler return water from the radiant loop.

secutanudu 02-28-2010 04:04 PM

Ahhh, I thought it mixed it with your domestic water. I was wondering where all that extra water would fit in :)

jaros bros. 02-28-2010 05:21 PM

Also called a mixing valve. Easy to install.

ink 02-28-2010 08:34 PM

As I'm in the middle of doing a hydronic radiant floor install in my kitchen, I can safely say that there is more to this then meets the eye. Do a lot of reading!

Things to consider:
-Pex diameter
-floor height will change (unless you do the joist install method)
-you'll need a separate zone for the floor, to include a zone valve (or flow-check), circulator pump, radiant manifold, mixing valve, and floor thermostat.

secutanudu 02-28-2010 09:02 PM

I was aware of the floor height change and I think you can use 3/8" pex (I think I read that).

I won't be doing the install, but the contractor/friend I have helping me has never done it as a retrofit, so I would like to research it myself.

Right now, I have a single zone on my boiler, with a circulator pump on the return side of the boiler. What is the best way to add a second zone? Add two zone valves just downstream of the boiler? Each zone would open it's valve plus run the circulator.

How do you do two zones with only circulator pumps? Would these pumps need to be downstream of the boiler? If they are on the return side, how does one pump not pump through both zones? If zone A's pump is on, does zone B's pump (which is not on) allow water to pass through?


secutanudu 02-28-2010 09:21 PM

Radiant manifold...i assume you need that if your room is big enough to warrant two individual feeds due to heat loss? If so, the bathroom is only 5' x 7', so I doubt I'll need it. I may need it, though, when I run radiant in my mudroom which is 9x14.

Are there instructions anywhere on how to install a mixing valve?

Edit: nevermind, found it here:

Only thing I'm unsure of now is how to add the second zone and how to do a floor thermostat. Why a flood thermostat instead of one on the wall? I plant to use the radiant floor heat to keep my bathroom to temp...

beenthere 02-28-2010 09:25 PM

Pretty much can't use one circ with a radiant and regular heating zone.

Need 2 circs for proper water temp control.

secutanudu 02-28-2010 10:01 PM

What would the ideal setup be then? Two circs downstream of the boiler? One would push to my normal zone, the other would push to my mixing valve-->radiant zone?

something like this look right? Do I need check valves on the boiler-side of each circ pump to ensure one zone doesn't pull cold water from another?

All times are GMT -5. The time now is 05:48 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
User Alert System provided by Advanced User Tagging (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

Search Engine Friendly URLs by vBSEO 3.6.1