Radiant Floor heat - insulating pipe in concrete

[premis]

I'm getting ready to build a house and plan to put radiant heat in the floors. On my basement level I will have two zones, the main zone inside the home (zone 1) and a 2nd zone which is a "shop/storage" area built under part of my garage using pre-cast (zone 2).

I want to use a single centrally located water heater in my mechanical room to run everything. In order to do this, I would need to run a single circuit from the mechanical room, through the Zone 1 floor and into Zone 2. I would bury this pipe in the concrete slab of Zone 1 just like the other pipes. My thought was to use pipe insulation like this on the zone 2 circuit as it runs through zone 1. Does anyone know if this can be done? The slab would be 4" so it would be enough to cover the pipe and the pipe insulation. I'm just wondering if this will be efficient and if I will have concerns of the concrete being weak. For what it's worth, 80% of the pipe run will be under a bar, so not in a traffic area.

 

[Chris705]

I ran my pipe for remote zones under my rigid insulation board. I put 2” Armaflex insulation on the 3/4” pipes. I dug a trench laid it in and covered with stone jut to top of pipe. If you go your route, in the slab, for sure it will crack. Maybe not an issue under the cabinets/counter but what about the adjacent space?

 

[yeldogt]

First -- what is the BTU needed for the spaces --- did you match this to a water heater output?

I'm assuming you will zone within the living space ... or will it have supplemental HVAC ?

Depending on the flow needed for the storage area it may be better to just hide the pipes in the wall behind the bar? My guess is it only going to need 1" piping.

You can always burry them but you want to channel them in and keep it all in the "system" above the floor insulation and VB ... just drop it a inch so you have 3" over the tube insulation

Don't place tubing under the bar for heat unless you want the bar storage to be hot

 

[HoosierBuddy]

If this is for your house, my advice would be to definitely get an appliance designed for space heating to heat your water. yeldogt is right. Step one is figuring out how many btu's you need. Personally I went with a wall mounted fully condensing modulating boiler to handle my in-floor radiant. A choice I have never regretted.

Phil

 

[premis]

Sorry for the slow reply, I must not have had my subscription alert on.

First -- what is the BTU needed for the spaces --- did you match this to a water heater output?

Yep, I plan to use a tankless water heater. I'll get one with enough BTUs

I'm assuming you will zone within the living space ... or will it have supplemental HVAC ?

Both. Zone 1 will have a standard HVAC system, the floor heat will just supplement that.

Depending on the flow needed for the storage area it may be better to just hide the pipes in the wall behind the bar? My guess is it only going to need 1" piping.

Do you recommend having a separate manifold in zone 2 and just run pipes through the wall from the water heater in the mech room to the manifold in zone 2?

You can always burry them but you want to channel them in and keep it all in the "system" above the floor insulation and VB ... just drop it a inch so you have 3" over the tube insulation

Do you mean something like dig a 3" deep trench, drop the vapor barrier into the trench, then 2" foam on top of the VB, then the pipes for zone 2 on top of that foam board, then lay another 2" foam board over the pipes, then top with the concrete?

 

[kj_mustang]

If zone 2 is large enough to require more than 300' of pex in the floor loop and run back to the mechanical room, than yes, you need to run a supply and return line to zone 2 and put the manifold in there.

 

[Jackfre]

Most tankless water heaters are not rated for closed loop heating. Takagi is the only exception that I am aware of. Many of the tankless water heater manuf do make combi boilers that will do dhw and space heat properly. You want this system to operate smoothly, That means, with your lay-out, that you will require primary-secondary piping and you want an outdoor reset control to get the best comfort and smoothest operation of the boiler.