Pex radiant--pros/cons of above/below floor?

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Old 03-06-14, 07:24 AM
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Pex radiant--pros/cons of above/below floor?

My wife wants radiant floor heat in our cottage so I'm going to humor her and pretend to consider it
I currently have a working standard cast iron boiler, copper fin tube baseboard system. The cottage is divided into 3 sections:
One end on a slab that will eventually be the laundry/mud room/closet space.
Center is over an unconditioned bare dirt crawl. Some excavation via buckets would be required to access the bottom of the floor boards.
Other end is over a basement.

New flooring is needed throughout so this opens up the possibility of installing the tubing above the existing floors. What are the cost/efficiency/comfort trade-offs of installing below using reflectors vs. above using those grooved panels?

Would such a retro-fit be a budget-breaker? We only go to the cottage a few weekends during the winter so heating efficiency isn't a big concern but keeping the existing boiler is important to keep costs reasonable.

Main reason I'm even considering doing this is I hate needing to design around/work around/decorate around baseboards.

 
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Old 03-06-14, 07:35 AM
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It's quite an expensive project. For one, you will need a new boiler and if thats a deal breaker, I wouldn't go any further.
 
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Old 03-06-14, 03:13 PM
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RD, is your tongue in your cheek? I can't tell? Why you thinking new boiler?

Guy, either method if properly done will work... as long as you can get the heat output that you need to meet the heat loss. Sometimes difficult to do so.

Gonna be a bit of work, and probably somewhat expensive, but do-able.
 
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Old 03-06-14, 03:47 PM
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Previously I had only considered tubes under the floor and that was a big problem for the slab section. AND the crawl section wouldn't be a picnic because the joists are only 6 inches over the ground in more then 50% of the floor. That's the reason for the bucket-brigade comment.

Saw an episode of This Old House recently where they were laying radiant on top and that got me thinking it might be far easier in a retro-fit to do it that way. I can sacrifice a couple inches of ceiling height and not miss it. I don't recall in the show if they put anything down on the cold floor before the grooved boards--any extra insulation needed?
 
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Old 03-06-14, 04:12 PM
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the joists are only 6 inches over the ground in more then 50% of the floor.
I'm not terribly claustrophobic, but I once worked for a couple years as electrician apprentice. We had a job where the journeymen needed a 'mole'. Guess who they picked? Right, the skinny kid apprentice... yes, no more than 6" between the WET ground and the floor joists, and it was a BIG ranch and the wires had to go all the way to the other side. I didn't last long on that job.

any extra insulation needed?
I think so... I wouldn't do it without insulation.

Indeed, from one of the PDFs below:

When Warmboard is being installed over joists,
a minimum of R-19 insulation is required
underneath the panels to prevent downward
heat loss.
Check out 'WarmBoard' products. Install PDFs here:

Installation Information | Warmboard, Inc.

Last I checked, the stuff was kind pricey. Haven't used it myself.
 
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Old 03-06-14, 07:02 PM
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Keep it simple... cottage needs to heat quick when you get there. Best designed radiant systems aren't designed to ramp hard. Although floor warming feels so good.
 
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Old 03-07-14, 09:37 AM
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Amen, Who!
I'm in my second winter owning this place and I've been keeping it at 50 while away. The cost has been more than I expected. I've read information on glycol-filled radiant systems like mine that says it doesn't slush and remains pump-able to below zero. Ideally I'd like to maintain 30 degrees but I'm concerned how long it will take to ramp up to comfort level when I arrive--and what stress this places on the cottage or heating system. It takes about 1.5 hrs to go from 50 to 65 with my 100KBTU boiler & baseboards.

My previous cottage was smaller, had no insulation at all, and heat was provided by 2 NG direct-vent wall heaters with tiny optional internal fan to improve convection. I kept the heat OFF all winter there and never had a problem. The coldest temperature I ever recorded there (on one of those max/min recording digital thermometers) was 17F but typically it would be in the low 20's when I would arrive late Friday evening & the heaters would zoom the temp up to shirtsleeve comfort in about an hour. The walls would glisten with condensation but the place was built solid and most the wall covering was wood planking and paneling so I never had any damage of any kind in the 6 years I owned the place.

I was hoping a huge radiant surface like the entire floor could heat up fast.

What kind of damage can be caused by such a fast ramp?

Troop--thanks for the links. I'll do some reading & see if the build-up is acceptable. If not--then at least I looked into it like I promised the wife I would
 
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Old 03-07-14, 11:52 AM
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What kind of damage can be caused by such a fast ramp?
I don't know that it's a question of " damage " as it is a question of whether radiant floor is even CAPABLE of ramping that fast, and in fact, it's probably not.

An advantage of hot air heat is that recovery time is faster... at least to get the AIR warm initially anyway.
 
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Old 03-07-14, 12:17 PM
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Is it a matter of the mass that is being heated? My baseboards are heating lightweight air & the air is then heating the objects--but really the only object I care about when I arrive is the bed
If the system can't immediately start warming the air inside at an acceptable rate then this is a show-stopper for me. I don't mind the floor being cold for hours but seeing my breath as I'm getting ready for bed isn't what I have in mind.


Reading over the Warmboard literature I noticed they recommend R19 under the sheets when installed on an existing sub-floor or over a crawlspace. But it can be installed directly on joists or a slab. This doesn't make sense to me.
 
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Old 03-07-14, 08:35 PM
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I am not even sure I would have a hydronic system there if you wanted to spend that kind of dough... I'd be upping and evening the insulation and draftiness, looking at simple solar and just living with a 2 stage something... Didn't say gas or oil? But either way, 2 furnaces?... a big one and a little one to maintain. Big could even be commercial/louder... If it only took an hour! ;-) And crank the music! LOL

2 Heat devices! Smallest just to maintain and big to heat that house up fast and economically. I would only have a hydronic system if I lived somewhere that I couldn't keep the house from otherwise freezing - simple water, even if it meant house sitting 2 labs and baking lots with the oven. ;-)
 
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Old 03-07-14, 08:48 PM
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How much is it worth if I could tell you how to make her super happy and you look like a rock star for under $500? Off the record of of course... L

There is a very simple solution here.
 
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Old 03-08-14, 03:30 AM
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heat

Remote control thermostat via internet or telephone. And electric blanket?
Steve
 
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Old 03-09-14, 03:12 PM
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Am electric blanket has been great for getting the bed warm.
A remote thermostat would be great but there's no internet or phone there. Kinda like it that way ;-)

So what's the $500 solution to warm floors?
 
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Old 03-09-14, 03:25 PM
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So what's the $500 solution to warm floors?
You a funny guy Guy! (ooops, I see you are responding to Who... I forgot he said that)

Turn your vacuum cleaner so the outlet points at the floor and let it run...

If you can stand the noise.
 
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Old 03-10-14, 04:39 PM
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Just find a clean key areas under the kitchen between the joists and add some plates and pex-al-pex there. Maybe three separate runs so that it is controllable, just by running 1 or 2. Just run it same zone pump as kitchen. Keep the runs short and they can easily just use the existing pump. You'll have a bit more recovery... as well as that warm floor feel (which will make you a hero to SWMBO - in front of the vanity in bathroom too) without too much hassle.
 
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Old 03-10-14, 08:30 PM
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So it's ok to run floor radiant as a branch off an ordinary 180 degree baseboard loop?
 
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Old 03-11-14, 05:56 AM
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You can, but it is generally recommended that the tubing be SUSPENDED in the joist cavity and a sealed air space created in the cavity by fitting foam insulation.

I'm not really clear on exactly what Who is suggesting... series with baseboard loop? 180 high temp staple up with plates? I wouldn't recommend that ... You want a hot stripe on the floors?

Guy, have you seen the Siegenthaler article: " A Little Floor Warming Please " ?
 
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Old 03-11-14, 09:27 AM
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I've never heard of suspended radiant tubes and I'm intrigued by the idea. I can sneak rigid foam and tubes between my near-ground-contact joists by working from excavated ends. A much better proposition than digging out the entire crawl to have access to the entire floor for stapling.

I asked about the 180 degree radiant loop because I thought it was just too hot and was never done.

I'll look for the Siegenthaler piece--is it a download?
 
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Old 03-11-14, 11:09 AM
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Pex supply dot com < just for an example
-price shop for these or better items
-contact manufacturer for compatibility (esp Wirsbo and P-A-P mfr)
-do some basic math on how things will change as you add heat underneath

I would actually say if the floor ends up too warm but you want it even it is as easy as finding, OSB, or plywood or even xps in 4' sheets, rip it into 4" x 4' pieces and screw them under the plates. Very simple to do. Just get screws "that" much longer.

PAP - " x 300' $110
Wirsvo trf plates 4" x 4' x " x 20 $120

And fittings and tools for the PAP as well as drill bits for the joists.

Possibly a sheet of plywood ripped into 4" pcs.

Only thing exotic you might want to add would be a FHV - like a TRV for the floor... but I would just do a test. Run the pipe. Keep shorts runs so it will flow.

Jeff... optimum length of " I.D. piping before its pushing back too much? 30'? 50?

I was spoiled, I had to have flow to keep the monoflo from acting goofy.
 
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Old 03-11-14, 11:11 AM
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I'll look for the Siegenthaler piece--is it a download?
If you google the title you will get a couple trade magazine 'hits'... I think one of them is PMEngineer or some such. You might have to register to access the article but it's free. The article presents a number of ways of adding floor warming to existing systems.

As I recall, one of them is a 'wild, high temp' arrangement.

Thing about the joist cavity insulation, you want those cavities to be as close to air tight as possible, to the insulation should be a tight fit. It might not be as easy as you think to get the foam insulation wedged into place to form an air seal.
 
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Old 03-12-14, 11:05 AM
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...want those cavities to be as close to air tight as possible, to the insulation should be a tight fit. It might not be as easy as you think to get the foam insulation wedged into place to form an air seal.
pretty much impossible on a 70 year old cottage and rough - sawn joists.
 
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Old 03-12-14, 11:26 AM
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70 year old cottage and rough - sawn joists.
Isn't that what "Great Stuff" is for?
 
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