Hydronic Radiant Alternative?

[Bob Winkler]

I picked up a special issue mag recently called "America's Best Home Workshops" by Wood magazine. It's actually quite good and one of the shops used a method of radiant heat that looks easier and may be an alternative for me. I'd like opinions on this. I quote:

"He settled on zoned in-floor radiant heat. On top of concrete slab he laid 30-lb builders felt and 6 mil plastic taped at the seams. Pressure-treated 2x6s were laid end to end as floor joists, followed by 2 layers of 2" polystyrene foam insulation in the bays, topped with sheets of Reflectix insulation. Runs of hydronic hose followed. Those were covered with Advantech, an oriented strand board-type subfloor material."

It goes on the talk about how he ran wiring and DC piping in the floor bays. It doesn't say anything about his furnace.

I'm interested in this concept because I have a concrete slab that I was thinking of covering with a wood floor. This might be a good way to add a wood floor and heating system for me. Here are some of my concerns/questions:

- can a conventional water heater be used (50 or 60 gal)
- how would the pex tubing be retained in the floor bays
- is the efficiency ok without specialized conductive subfloor treatments such as Warmfloor subfloor or aluminum plates

Thanks for any input from you radiant experts out there.

Bob

[Faust M. Ruggiero]

I have radiant heating in my house. Warm floors in PA winters are a treat. My system dates back to 1949 when my house was built. I studied the modern methods as a solution for an unheated sun porch.
In answer to your question; the insulation and heat reflective materials are to keep the heat from radiating down instead of up into the floor. They are needed. The plastic acts as a moisture barrier and is definitely necessary. The sub flooring has grooved routed out as channels for the tubing. Plastic tubing is an excellent choice since it requires no fittings to round corners. The hot water heater probably won't work but a plumber could tell you more. The system will require low temperature water, about 100 degrees or less. Hotter than that will cause hot spots in the floor, a good way to learn to dance.http://www.sawmillcreek.org/images/icons/icon7.gif
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[Peter Rawlings]

Bob, is this an existng building or a slab you intend to build on?

[Ken Fitzgerald]

Bob,

It's been 5 years since I researched in the floor radiant heat so somethings have probably changed.

Do a search. There are a number of national companies who do this and provide some pretty good design advice free.

The problem that stopped me, no water source in my shop. It got really expensive to have a system designed, built and approved to meet the local building codes.

Radiant heat is typically a little more expensive up front but in the long run it should pay back.

[Dave Schreib]

Unfortunately, I dont have answers to your specific questions but I would like to put in a plug for the radiant floor heat. We have it in the finished portion of our basement - it was installed then the concrete was poured on top of it. It is a fantastic luxury. Temperature wise, the basement is the most comfortable space in our house.

Rather than build on top of the concrete floor with 2x6s, would you consider breaking up the existing concrete and doing it "right"? That would save you from losing ceiling height and keep you from having different flooring heights. I bet that much of the work would be DIY friendly. Good luck

[Bob Winkler]

To answer some of the questions and comments.

This a workshop I built this summer on a concrete slab. I didn't have time to plan and execute a "proper" radiant pex layout in the slab due to planning my daughter's wedding which occurred during the building construction.

The current ceiling height is about 10', so I would be willing to sacrifice some height. Since I would like a wood floor for comfort and aesthetics, I was considering 2x4' floor structure covered with subfloor and hardwood. I would run some wiring (not too much) and some compressed air in the floor. I won't need to run DC piping.

One radiant option is Warmboard which is a 1 1/8" subfloor and has the routed grooves for pex. The hardwood would go right over this. The problem with this is that the Warmboard is very expensive and must be designed to fit the space.

Another option is as described in the article I mentioned, which is pex tubing under "normal" T&G subfloor.

A final option is to skip the radiant heat and install a wall furnace or other hot air heater. The wood floor would still insulate me from the slab.

And Ken, I also don't have water plumbed and was going to use a water/glycol closed-loop system.

Thanks for the comments and opinions.

Bob

[Peter Rawlings]

Bob, what you're proposing is possible, but I might modify method from what you originally posted. The BIG key is getting the slab insulated, since it sounds like there's no insulation under it. Is there a vapor barrier under slab?

You want the bulk of the heat to radiate up, slab will act like a huge heat sink without it, increasing system cycle times and temps. The economies of radiant will be lost. Another thing to consider is the glycol. It actually reduces the efficiency of the system somewhat. Hydronic heat doesn't respond quickly like forced air. It takes hours to raise temps a few degrees. I run straight water in a closed system all winter long at 60 degrees, but I'm in the shop almost every day.

It's not cheap to do well, I'd put down at least 2" of extruded foam with sleepers on top, likely 2x4 flat with your pex and other stuff in the 1 1/2" void. Decking and finish floor on top of that. Be careful with nail length.

The other possibilty would be gypcrete on top of the foam/ pex. This would give some of the benefits of using the concrete as a radiator.

The reality is that either one of these will likely be 4 or 6 times more expensive than a forced air furnace. To give you an idea, the system heating our 2800 sq.ft. building was around $7.5k for mod/con boiler, manifolds, pumps, pex and pro design. I did the install. The up side is I maintain that building at 60 throughout the southern Idaho heating season for around $35-45 a month. Highest ever was around $60. We intend to be here till we leave this earth.

I'm sure it could be done for less $, but I really didn't want to engineer this seat-of-pants. Although after installing, I'd feel more comfortable with doing that.

There are other possibilities like panel radiators, which might also make sense. Might be worth it to consult with a pro for most bang for buck. I can reccomend a couple depending on where you are.

Peter

[Tom Godley]

Bob -- like others have said -- insulation is the key for the system to work efficiently.


I built an addition onto my house -- extending the current radiant heated wood floors into this new area. We built a conventional block foundation and then poured a slab a few inches lower then the current floor depth. The slab had insulation under it as well as on the sides at the block wall plus a vapor barrier. I then used another vapor barrier and 2x6 pressure treated lumber on its side as nailers on top of the slab with 1" foam placed between the 2x6's. I used Warm-board and then the new floor. Warm-board is a great product -- and it actually was the cheapest and easiest way to do this over a slab. It is very easy to lay out and work with.

The addition of the aluminum allows the system to conduct the heat out of the tubes and onto the floor surface quicker and using lower temperatures -- this increases response time an allows for lower water temps -- this in-turn cuts operating costs.

Many systems use hot water heaters for the heat source -- and the tubes can be attached using many different systems from staples to specialized clips for ridged foam.

I would not use any builders felt with tar in the design! - I remember reading this article.

I am about to have a new floor poured in 1/2 of my shop and I am going over all the pros and cons of all kids of floors at this very moment!

[Damon Marxer]

Bob:

I have not seen the issue but I installed radiant heat in my outbuilding this summer. It was new construction so the pex was laid before the cement was poured. In your case, it sounds like the slab is already in. It is a great heating system and I wish my house had it as it is so nice.

One question I did not see is if you insulated under the slab with 2 inch foam and visqueen? I would think your biggest issue adding it after the fact would be heat loss going down. With that said, I think you could lay sleepers down and run the tubing between the sleepers and then fill it will cement or even sand. You might want to put down a reflective material first to reflect the heat upward. I have 500' that I was going to use for the upstairs system but never used it as I found insulation with a reflective back. It is just a thin material that is shiny on one side.

I worked with Radiantec (http://www.radiantec.com/index.php?gclid=CPWqwcLMiZ8CFQ0hDQodNjWAsA) and they were very helpful as I am certainly not an expert in this area. I would give them a call and explain your situation. I am sure they could come up with a system that would work. Their website also has manuals you can download that will show an option similar to what you are explaining.

Also, I wanted wood floors similar to you and finally nixed the idea as it just became very expensive. The Warmboard you mentioned is good and reflects the heat upward but it is extremely expensive stuff. However, if you go the sleeper method you could still do wood floors. Just be very careful when nailing it down and I would use short nails.

Good luck!

Damon

[Jim Foster]

If you ask a plumber to price this out, it's very expensive. Also, I think the subfloor when done well uses up a few funds.

To get the best efficiency you need some type or radiant or conductive material around the PEX, and you can hook the radiant up to an existing boiler without too much trouble. (if you have the capacity on the boiler for the extra BTUs) I do not now how it would work with a typical water heater becaue in general the radiant water runs constantly for many hours a day.

The easiest way to lay down PEX on a floor is to use Warmboard. The warmboard alone will be several thousand dollars, it helps radiate the heat so it's important to use a good base for the PEX. Pex tubing is also expensive. You will also need a manifold with several ports (300 ft runs are a rule of thumb and you may easily need 900ft pex) and a larger diameter pex for supply/return to the boiler, unless you connect with copper. On the boiler you will need a three or four way mixing valve (Radiant floor water temps are lower than standard boiler temps, so you mix the boiler water with return water and cold water to get the temp down). Depending on the flooring material like hardwood flooring you shoud have an electronic temperature control managing the mixing valve so you don't "dry" the floor out too much with high temps. (Since the radiant is very slow to respond to temp differences in the water its a good idea to have it properly controlled from the start)

When you price out the subfloor and radiant in a compete estimate, I can only imagine the number will be surprising.

One consideration is that the concrete provides a much better damper for machine tools and a much more solid base. Also making holes in a radiant floor can be fatal to the PEX tubing. You can fix it pretty easily, but the flooding will be a pain to clean up under the subfloor.

I think for a pre-existing space, a great idea I've seen is to add the mini-split AC/Heating units that can double as AC in the summer. The reason to have AC is just as much for dehimidifying as cooling, which prevents rusting. One of the forum members mentioned once you get over 53% releative humidity can bloom rust. The mini-splits can come with several "zones" or wall units, so you can spread them out nicely to over a pretty good size space.

I added radiant flooring to a large slab on grade remodeling project we did and did exactly what you are suggesting. I put down about 800 sq-ft or so of Warmboard and PEX as you describe for several rooms and as I mention above it's pricey when all done. (If I recall, the warmboard alone was 6K, this price might also include the 3, three or four port manifolds I needed) I also laid down PEX under my new garage floor (concrete) and after adding up the cost of the PEX, insulation, manifolds, mixing valves, etc... It was also pricey. The garage is nice when you have to lay under a car in the winter or spend time working on a car. My shop is above the garage and has no heat currently (If I heat it, it becomes finished space and subject to higher taxes. They let me go on the garage because I was able to convince the assessor that even though it was heated it was still just a garage.) I'm using a kerosene heater in the shop and it would be nice to have a better heating setup, but I do not think I would notice the benefits of radiant in the shop.

I don't want to damp your spirits on the idea, but hopefully you'll be ready for any sticker shock when you look into it a little closer.


I picked up a special issue mag recently called "America's Best Home Workshops" by Wood magazine. It's actually quite good and one of the shops used a method of radiant heat that looks easier and may be an alternative for me. I'd like opinions on this. I quote:

"He settled on zoned in-floor radiant heat. On top of concrete slab he laid 30-lb builders felt and 6 mil plastic taped at the seams. Pressure-treated 2x6s were laid end to end as floor joists, followed by 2 layers of 2" polystyrene foam insulation in the bays, topped with sheets of Reflectix insulation. Runs of hydronic hose followed. Those were covered with Advantech, an oriented strand board-type subfloor material."

It goes on the talk about how he ran wiring and DC piping in the floor bays. It doesn't say anything about his furnace.

I'm interested in this concept because I have a concrete slab that I was thinking of covering with a wood floor. This might be a good way to add a wood floor and heating system for me. Here are some of my concerns/questions:

- can a conventional water heater be used (50 or 60 gal)
- how would the pex tubing be retained in the floor bays
- is the efficiency ok without specialized conductive subfloor treatments such as Warmfloor subfloor or aluminum plates

Thanks for any input from you radiant experts out there.

Bob

[Bob Winkler]

Thanks for the excellent and very detailed responses. I really appreciate them. Based on these and my own research, it is clear that radiant heat is certainly a permium heat at a premium price.

What I decided to do for now is to invest in high-quality insulation and minimize my heat loss by also adding an insulated wall enclosing my overhead doors. This "cold room" will act as a buffer from the outside, and be used for lumber and misc. storage. I will access the heated shop from this room via either nice double insulated glass french doors or double steel doors.

For heat, I have ordered the 5KW Dayton workshop electric heater. It is inexpensive to purchase and easy to install. If at some point in the future I can't tolerate the electric bills, perhaps I can revisit gas direct vent heaters. For now, I don't want the expense of the gas heater or hassle of tearing up my yard to run the gas line.

Bob

[Jeff Nolan]

instead of a hydraulic radiant heat solution for this application, can anyone identify a reason not to go with a NuHeat electric mat system? I used this in the bathrooms of my house and it's fantastic, and with no valving, fittings, piping, etc. it is certainly a lot simpler in design.

[Jim Foster]

When I tackled the radiant flooring described in a post above, I looked at NuHeat also for a floor that I could not install hydronic radiant on/in and it was also a very premium priced product when calculating how big of a mat was needed and how much heat you would get out of it. Also the areas we were considering were already plumbed for baseboard heating, and would have needed additional wires run, so the cost differential was significant.

That being said, I liked the idea of using NuHeat and had hoped to use it for some areas of my house, it just did not pan out for me. Maybe it was really because of the hangover I had from the cost of putting the PEX based radiant in. :)



instead of a hydraulic radiant heat solution for this application, can anyone identify a reason not to go with a NuHeat electric mat system? I used this in the bathrooms of my house and it's fantastic, and with no valving, fittings, piping, etc. it is certainly a lot simpler in design.