Onix

Nick_16

I did a radiant heat loss calc. for my 1200 sq. ft. home and only came up with 29,000 BTU/hr. heat loss on a -5 day outside. Could this be right? This is using the Radiant Works software. I did heat loss with the Slant Fin software and it came up to much more like 38,500. With both software programs, I designed 5 zones. My bedrooms have thick carpet and pad. I thought I would need very high temp (145) to make it work but Radiant Works says 134 deg. to get 17.06 BTU/hr/sq.ft. with stapling up onix. It says 107 deg. to get 9.3 BTU/hr/sq.ft. with onix also. This is under thick carpet and pad.Also, I would like to staple up onix rather than pex with plates if I could get away with it. All of this is staple up over a fully heated basement. Please tell me some of your thoughts on this. I want to be sure before I do it. Also, who sells Onix online or by catalog?

hr

Make sure

you have an accurate R value for that pad and carpet!

Thick wool carpet could be R-2 or more and urethane pad another R-2.

You should be able to get r values from the pad manufacture, maybe the carpet manufactures. Radiant works should allow you to input the total R value. Run it with a higher R to see the changes.

It's not uncommon to see 15- 20 BTU loads on an average, well insulated home.

hot rod

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Nick_16

Radiant Works says for an R-value of 2.3 for "Heavy Carpet & Pad". That's what I was going by. Where can you buy Onix?

hr

I'd still like to see an actual

R value for YOUR pad and carpet. Carpet on the RPA calculator runs from .6 to 2.2 and a 1.5 multiplier if it is wool! Foam pad 2.0 for 1/2"

The floor covering R value is where I have found staple up systems to "choke" when design days come around, is not properly accounted for.

I'm not convinced you want to drive them much over 145- 150, as the plywood and engineered "glued" product manufactures start to squirm. Elevated temperatures, the wood people tell me, will cause the glues and fiber to breakdown after time. There is around a 7-11° delta t between the fluid and outer wall temperature with a thick EPDM tube.

Use caution is all I will say.

The current list price for 1/2" Onix with the recent $ increase is $1.94. I can get PAP and plates for less than that and I feel better about the performance.

hot rod

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Nick_16

Okay,

the carpet isn't wool, I think it is polyester, 3/4" or 7/8", pad is the standard carpet pad 1/2" or 3/4". So should I design the system around a R-4 value? It is a Mohawk carpet and when I called to ask for specs for radiant heating, the woman acted like I had lost my mind. She didn't even know what it was. Also, can radiant heat loss calcs very as much as I mentioned above from regular hydronic heat calcs?

hr

I think the carpet and pad manufacturing association

would have better data. I believe the RPA has some contact info. We have had floor covering and carpet folks speak at RPA metings over the years.

Yeah, I would error a tad on the safe side. What do you have to lose. Hard to fix an underperformer, without cranking 'er up. Impossible to fix if insufficient emmiters were installed. Other than adding supplamental heat.

Yes, heat loss cals can and do vary. We did a side by side comparison years ago at the RPA. Even with radiant specfic software, from various nmanufactures, there were some wide "bottom line" spreads when the same exact spec and inputs were used.

While most, or all, radiant design software is Manual J based there have been some allowances "built in" for radiant designs.

I believe the Slant Fin is intended for HW baseboard, but their numbers have always worked for my BB designs. Hard to argue with that. Maybe their is a bit of fudge in their numbers.

With todays modern modulating equipment a small over kill in sizing should not effect the performance or operating cost. IF you can assure the heat gets to the space.

Constipation in a radiant system is an ugly thing. As the name implies

hot rod

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Nick Dearing

Thank you

Hotrod. I will try it a little higher. Just like you said, you can easily turn the system water temp down but only up to a certain extent. I have joist that are 14" on center and I would like to run two sets of 1/2" pex tubing with plates in each joist space. are the plates thin enough that you can staple right through them? Or do they have holes to put in a small nail or staple? Also, in the future, if I take up the carpet and put in Pergo or Tile, can I remove a few plates if needed and just staple the tube to reduce heat transfer? Thanks again.

Ragu

Hot Rod

I really think you have created a new industry term that says it all in a nutshell: "Radiant Constipation". I, too, have suffered from this afflication. Any problems I've ever had with underheating radiant was never a boiler or tubing issue; it was always a delivery problem. Thanks.