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Lets Discuss Radiant Floor Heat

Lee

Guild of Calamitous Intent
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Specifically hydronic pex in slab. Tell me about what you're using, why, what you like, what you don't like? Closed or open system? Glycol? Heat exchanger, boiler, water heater, tankless, solar?

How many zones do you have and why? How do you control your zones? How many square feet are you heating with how many BTUs?

I'm in central AR, I've talked to 2 different contractors who claim it's not cold enough here to need foam insulation below slab, that washed gravel is sufficient, and they've built several systems without foam. Sound reasonable?

Anyone using solar water heaters?

I'm considering solar water heater(s) on the roof, supplemented by a tankless water heater. Anyone using solar water heaters?

I'm going to have an upstairs, semi-finished ~1K sq ft, mezzanine, mechanical/storage/bonus room, I'm thinking about doing in floor heat up there too, maybe just hydronic baseboard. Anyone used any of the plywood floor pex systems?
 
Definitely insulate the slab. It's not something you can go back and do later.

I'd do a couple of zones for your bedrooms/bathrooms downstairs, one for the kitchen/utility rooms/dining room, one for the living room.

Upstairs, definitely do the radiator instead of infloor. Supposedly, you can insulate enough, but why waste the heat in the joists when you can put it in the room instead.
 
My tubing is installed with slab but rest of build not even started yet . . . . . "Boiler" is a misnomer, you do not want to boil anything. I would insulate with foam. Contractor says :lmao::lmao::lmao: That translates to contractor does not want to bother to do it correctly. Does either contractor live in a radiant slab heated house ?? This is GOVERNED by code. What does yours say ??
 
Been on a lot of jobs that were in floor heat. Most use clear pex, triangle tube boiler with a few grundfos external pumps to keep the glycol moving. The plywood that has groves is a nightmare it seems. Be prepared to router the shit out of it for new routes. If you can’t sacrifice 1 1/2” of your floor and do gypcrete then I’d just do staple up under the existing plywood,


I always thought if you have ac you might as well do forced air? Why you want to do radiant heat there?
 
Find new contractors... you need to insulate under the slab... here's how it's done... Insulation, Welded Wire to tie the tubing down, rebar on top of that. Generally, a 5" pour to be safe.
Gentry Progress 2016-09-14 005.JPG
 
Foam is cheap, why would they not want to use it, doesn’t have to be spray foam.. this type is used indoor too.

B38963BE-DA4D-4E1A-9DE4-3AC3AE01E1EF.jpeg
 
Don't use glycol, it takes about 40% more energy to heat it. Also keep the pex within about 2 inches from the top of the slab. IMHO those pictures posted above show pex installed wrong. They make special stand-offs to support the pex and the rebar.
https://www.youtube.com/watch?v=XvE-du6xMco
 
Worked at a place that I helped run the tubing in when they were building a new building. There's a length limit to how far you want tubing to go (want to say less than 100'). We had the warehouse section as one heating zone (multiple runs of the tubing) and then different offices on other zones. Definitely insulation under the slab. They used glycol to heat because if the building ever was not running in the winter they didn't want it to freeze.
 
Why does it HAVE to be foam insulation? I would think rock would be a decent insulator for where op lives?


I've been watching a guy on YouTube do a shop/home build. They did radiant floor heat in the whole thing. They used a specific foam that had grooves for the pex. They are also in canukistan where they have to say "oh its warm today, probably plus 30*" :laughing:

I would think having the pex 2" from the surface would be great in a house, but not in a shop.

Ever since we stayed in a place with radiant floor heat (in Tahoe during Thanksgiving) I am a fan. No cold spots, no cold feet, no "oh man it's kinda chilly in here" *heater kicks on* 5 mins later, "Fuck it's hot in here"

I'm trying to learn as much as possible, so I'll be watching this thread.

Still curious about wood fire heat as a primary "boiler"
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Yes to the insulation and don't forget insulate the edge too. Glycol for real cold areas to prevent freeze up . If you do an open system you will get corosion ,would need bronze circulators . And with a radiant slab pick your temp and leave it . Use a few base boards or the wall mount hydronic heaters with a fan to bring temp up. If you come home and are cold and bump t-stat up your floor is not going to instantly get warmer. Just figure out how many btus you will need and pick a heat source.
 
Yes to the insulation and don't forget insulate the edge too. Glycol for real cold areas to prevent freeze up . If you do an open system you will get corosion ,would need bronze circulators . And with a radiant slab pick your temp and leave it . Use a few base boards or the wall mount hydronic heaters with a fan to bring temp up. If you come home and are cold and bump t-stat up your floor is not going to instantly get warmer. Just figure out how many btus you will need and pick a heat source.

Yes, that was the first thing we learned about floor heat. Its slow to react. Which is good and bad. We were told to just set it to 66-67* and just use the gas fire place thing for when you first wake up or whatever.

The one thing I didn't like about that place was that the tile shower was always freezing, I always wondered if there was a way to run the pex behind the walls of the shower.
 
There are 2x4 foam interlocking panel that have a round nub grid pattern on that the the pex wedge's into . I have one and can get a pic tomorrow.
 
Still curious about wood fire heat as a primary "boiler"
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what do you want to know? My dad has one. He upgraded to a ~$7K unit, but he puts wood in it 2x/day, and it heats a 40x40 shop and a 2800' sq ft, 2 story house (and the water heater) just fine throughout Michigan winters.

I want to say he probably burns....15-20 cord/year?
 
Yes, that was the first thing we learned about floor heat. Its slow to react. Which is good and bad. We were told to just set it to 66-67* and just use the gas fire place thing for when you first wake up or whatever.

The one thing I didn't like about that place was that the tile shower was always freezing, I always wondered if there was a way to run the pex behind the walls of the shower.

Yes you can do that , best if on a separate zone with increased water temp . I have wall in my mud room that is all cultured stone that has pex behind it.
 
what do you want to know? My dad has one. He upgraded to a ~$7K unit, but he puts wood in it 2x/day, and it heats a 40x40 shop and a 2800' sq ft, 2 story house (and the water heater) just fine throughout Michigan winters.

I want to say he probably burns....15-20 cord/year?

That was kinda my idea, big wood stove in a shop with the radiant heat ran through as well, then a gas or electric backup as well. I'm not spending $7k on a wood stove though, so I was just wondering how they work. My biggest fear would be over heating the fluid.

Yes you can do that , best if on a separate zone with increased water temp . I have wall in my mud room that is all cultured stone that has pex behind it.

Makes sense I would think if it was right behind the tile, it would heat up quicker than the slab? If the temp is higher would you need a dedicated heat source?
 
That was kinda my idea, big wood stove in a shop with the radiant heat ran through as well, then a gas or electric backup as well. I'm not spending $7k on a wood stove though, so I was just wondering how they work. My biggest fear would be over heating the fluid.



Makes sense I would think if it was right behind the tile, it would heat up quicker than the slab? If the temp is higher would you need a dedicated heat source?


his is an outdoor boiler - not a wood stove.

1200px-Heatmaster_Outdoor_Wood_Boiler.jpg



You won't like a wood stove with the fluid run through it - it'll be too hot or too cold. His unit is entirely self contained, runs on a standard 115v circuit.
 
his is an outdoor boiler - not a wood stove.




You won't like a wood stove with the fluid run through it - it'll be too hot or too cold. His unit is entirely self contained, runs on a standard 115v circuit.

My thought was why not have it in the shop, then get the benefit of it heating the air in the shop as well.

That's my worry. I would think you could design a system to either bypass the woodstove if it's too hot or add gas/electric heat if it's too cold. How does the furnace keep an even heat?
 
How does the furnace keep an even heat?


it's got a temp sensor for the fluid/inputs from the various thermostats, via the zone valves.

At it's basic level, it's trying to keep the glycol (or water, or whatever) at a set temp. zone valves open, colder liquid cycles through, furnace opens the damper, and lets more air in, which burns the wood, which makes the liquid hot.
 
My thought was why not have it in the shop, then get the benefit of it heating the air in the shop as well.

That's my worry. I would think you could design a system to either bypass the woodstove if it's too hot or add gas/electric heat if it's too cold. How does the furnace keep an even heat?

Quite well actually! They literally shut the air off to the combustion chamber, t Yhey have high and low limit aquastats that are set about 10-15 degrees apart. Mine maintains constant temp all winter long. I don't have radiant but have heat exchangers in the house. If it was in the shop you wouldn't really get much heat off it, they are insulated pretty well, just put in a Modine type heater in the shop, or radiant if you can.
 
Quite well actually! They literally shut the air off to the combustion chamber, t Yhey have high and low limit aquastats that are set about 10-15 degrees apart. Mine maintains constant temp all winter long. I don't have radiant but have heat exchangers in the house. If it was in the shop you wouldn't really get much heat off it, they are insulated pretty well, just put in a Modine type heater in the shop, or radiant if you can.

That's right, I remember seeing a video of one of those furnaces. I forgot that they control the flu and intake automatically. They are pretty slick.

I'm sure you wouldn't get much heat off of that style, they're designed to be outside, so I'm sure they're super insulated.

Like I mentioned, I'd be fine if it wasn't hot enough to heat the fluid on its own, but I don't know what would happen if it got too warm. I'm also not sure how much of a coil it would need, or where to run it:laughing:
 
That's right, I remember seeing a video of one of those furnaces. I forgot that they control the flu and intake automatically. They are pretty slick.

I'm sure you wouldn't get much heat off of that style, they're designed to be outside, so I'm sure they're super insulated.

Like I mentioned, I'd be fine if it wasn't hot enough to heat the fluid on its own, but I don't know what would happen if it got too warm. I'm also not sure how much of a coil it would need, or where to run it:laughing:

From my understanding of radiant heat and an OWB (outside wood boiler) you would have to have an indirect water to water heat exchanger, the temp of the OWB is somewhere around 165-175 deg F and radiant wants to be a lot cooler than that. Part of the equation is storage, that aids in the consistency of the temps. Mine the draft induction fan is set to come on at 150* and go off at 165* I put wood in it twice a day, 7 and 7 no matter the weather, you just have to learn to adjust the amount according to the outside temps.
 
200' max loop with 1/2" pex. Spacing about 10" apart. Insulating the outside edges is probably the most important. Foam under is best, another not as good option are the blankets, looks like a black and orange tarp with some foam inside. I would not go less than 2.5" min from surface, too much chance for getting hit with a nail or tapcon from an interior still plate, and your crack control sawcuts. It won't stay exactly where you left it as they pull up the mesh/rebar mat when they pour. If your doing the work of laying the pipe, make a tool with two spaced apart notches and a handle. Makes it much easier to space and tie down.

My place was big so I could not run all the loops back to the mechanical room. I ran sch40 pipe with high temp water to different areas and mixed it down to the proper temp at the manifolds. We have a primary boiler loop with 3 secondary loops for heat and one for hot water. Basement, upstairs, and garage. Most efficient to heat the whole mass to one temp and leave it.
 
With the outdoor boiler most are an open system ,so a hydronice plate exchanger can be used. This way you would only need 1 corosion resistant circulater. The rest of system can be the typical closed. So if you have a gas/oil/electric heat source in your home and set the aquastats accordingly when your fire goes out or not home the regular system will take over. The system could also be set up with mutilpe temps using zone's and mixing valves, so your radiant could be 85-100 deg, baseboard 175 deg, and 140 deg for domestic hot water which there are a ton of ways to achieve that. And for an open system on a wood furnace you can only put the unit lower down hill from house as the height of vent unless you extended it . Otherwise the water will never stay on line to house. And you always have to add water too, some have a float deal that keep them filled.
 
200' max loop with 1/2" pex. Spacing about 10" apart. Insulating the outside edges is probably the most important. Foam under is best, another not as good option are the blankets, looks like a black and orange tarp with some foam inside. I would not go less than 2.5" min from surface, too much chance for getting hit with a nail or tapcon from an interior still plate, and your crack control sawcuts. It won't stay exactly where you left it as they pull up the mesh/rebar mat when they pour. If your doing the work of laying the pipe, make a tool with two spaced apart notches and a handle. Makes it much easier to space and tie down.

My place was big so I could not run all the loops back to the mechanical room. I ran sch40 pipe with high temp water to different areas and mixed it down to the proper temp at the manifolds. We have a primary boiler loop with 3 secondary loops for heat and one for hot water. Basement, upstairs, and garage. Most efficient to heat the whole mass to one temp and leave it.

How big is your place? We're building 60x100' metal building with a 25x40' apartment in a corner. I've not attempted to figure it out for sure yet, but I was thinking that we'll have to do something similar, with 2 sets of manifolds, one near the apartment and one more centrally located for the shop.



Everything I've read, and all of the YouTube videos I've watched have all used foam insulation under the slab. I was really confused, when 2 different folks told me washed gravel was fine. My brother is just about finished building his McMansion by the lake, it's slab on grade with radiant floor, and they didn't use foam under the slab either.

I've seen the foam that kind of looks like Legos for routing the tube, I believe I saw that on This Old House. I'll look into it, but knowing me, foam board, weld wire, and zipties are probably the route I'll take.

I get putting a perimeter layer of foam around the slab, but what about overhead doors, or I guess any doors for that matter, how do you thermally isolate the slab from the outside apron or sidewalk?

I've seen the plywood or OSB, kind of looks like a zip panel with channels routed in it for pex, I thought that would be worth looking into for upstairs. I'm not real interested in pouring concrete up there, so I may skip in floor heat there.


Any thoughts on solar water heaters?

Sounds like most folks are using a "boiler" or more traditional tank style water heater instead of tankless.

Do you need a pump for each zone, or just have a thermostat control a solenoid valve for each zone?
 
Is natural gas available? If so why discuss any other heat source?
Put in a natural gas hot air furnace to heat up the air quickly when you want to work on something.
 
Is natural gas available? If so why discuss any other heat source?
Put in a natural gas hot air furnace to heat up the air quickly when you want to work on something.

No, rural area, but I'll have a gas range in the kitchen so I will have a propane tank.

I grew up in a home with wood fireplaces inserts and a wood furnace in the basement, I'm not dealing with that noise ever again. If I ever have a wood fireplace again, it'll be purely for ascetics or emergencies. We did the pellet stove thing for years too, I'm done with that as well.

I, haven't poured the slab yet, insulation and pex isn't that expensive, so it seems like I might as well set myself up for radiant while I can.
 
At the doors run the foam up to the bottom side of the apron slab, then use an expansion joint between the two. Foam is best. Depending on climate and average ground temp it makes a difference in what is lost to the ground and how fast. Higher temp differential the more energy lost. My basement is dug into the hillside 15' deep and ground temp is somewhere in the 50s. I set that t stat to 55 all winter and It will maybe come on a few times in a season.

The house is roughly 32x100. Mechanical at the far end in the upstairs car garage, I couldn't pump low temp water all the way around from there so I have boiler temp water going to different mixing stations.
 
https://www.isibp.com/products/insul-tarp-under-slab-insulation/
Screenshot_2020-08-30-22-23-52.png

There is also this stuff too. I used this in my house and don't have any complaints. As far as a thermal break for the door I have none on mine, con is heat loss,pro is when it snows it stay's melted in front of door 12". To do over I think I would use 2" foam then protect that foam edge with 2" x1/4" galvanized steel. Zone valves take up less space , my preference is to use circulators with the b.v. flange on either side in pic.
 
That was kinda my idea, big wood stove in a shop with the radiant heat ran through as well, then a gas or electric backup as well. I'm not spending $7k on a wood stove though, so I was just wondering how they work. My biggest fear would be over heating the fluid.

use a thermostatic mixing valve
most interesting setup I've seen was a wood boiler and some old water heaters as storage tanks (all at atmospheric pressure), you get all that mass up around boiling during the day, the valve keeps the water in the concrete loop from getting hot enough to crack the slab, and you can supposedly go a couple days between fires if your insulation is good enough.
 
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