in floor heat between joists, 24" on center with 3" thick wood floor

ddd

What's the best way to go about heating the house through the floor? House is 24x32 with a 2nd floor & sits on a 4ft crawl space.

Bob Bona_4

It all starts with a radiant heat loss and design to see if the floor can produce enough heat to condition the space.

hot_rod

Good chance you will need to install the system on top of that much wood floor. 3" of softwood would be around a R3.6, it would be tough to get an underfloor system to perform under that much insulation.

Only a careful load calc and design will tell you. The room by room load calc will tell you what each room needs to maintain a comfortable condition. The radiant design will indicate if the floor is capable of covering that load.

Mixing radiant floors with radiant walls, ceilings, or panel radiators is another common installation. insist on warm floors for kitchen and baths, in my opinion.

Also pay attention to the structural framing, if you are considering adding a overpour like gypcrete.

Gordy

With under floor radiant in your case you are already dealing with trying to push heat through an r 3 worth of flooring. As Bob said you need a heatloss calculation to see how many btus a square foot is needed to heat the space. Then you will know if the under floor type of install will do the job.

ddd

I've had multiple contractors here to give me quotes. One wants to use 1/2" pex tube & transfer plates with 2 runs between joists. Another wants to do the same, except do 3 runs between joists. Then another contractor informed me yesterday that neither of those will penetrate the floor and that I should use copper pipe and fin tubes between the joists instead and use convection action by allowing air to enter and escape the joist area. This contractor is stating that the pex tube heat will most likely transfer more to the crawl space by using the standard Astro Foil reflective insulation, which is what the first two contractors, who both have done a 'radiant heat loss and design' recommend. What is your comment on these two types of systems?

Gordy

Astro foil is garbage. So I would assume over the top is out of the question? What about radiant ceilings?

ddd

This is an existing home. We think we will need to run baseboard heaters on the main level and upper level, in addition to the tubing between the floor joists. Our floor will at least be warm then, instead of cold in the winter. And we'll have the warmest crawl space around!

So what is the best way to insulate between floor joists after we have installed the pex tubing and transfer plates, so that the heat radiates up thru the floor instead of down to the crawl space?

Zman

There are a few ways to slice this.
If you are going to do it from below you must use plates. 3 per bay would be good.
You may have have to run fairly hot water temps.Pex-al--pex will help minimizes the expansion noise.
As for insulation, the most economical would be foil faced fiberglass.Put as much in the bay as you can fit, leaving an airspace of 1 1/2" on top. Pay close attention to the insulation at the exterior rim joists. It may be worth applying spray foam or at least crack sealant and lots of fiberglass at the rim. I know folks on here have sprayed foam directly to the tubing and plates, I have feared damaging the tubing and have only done this as a last resort for exterior soffits. Even then I would suggest some tubing protection.
We are all just guessing here without more details.
Are the joist ends insulated?
What is the heat loss per foot of the area?
This all come down to the heat loss, if it is too high, you will have to resort to either adding insulation or emitters. In the long run insulation is cheaper because you only pay once.
Carl

Tinman

Lots of great answers here from lots of knowledgeable people. Ultimately, you're going to choose from one of the above mentioned contractors whose ideas/opinions are very different. In my opinion, whomever you choose needs to be able to back up their ideas/opinions with MATH. They need to be able show you, prove to you, that their method will work. The only way to do that is with MATH. They need to input all kinds of information from your home and do not only a heat loss calc., but confirm water supply temps, floor surface temps, gpm, head, etc.

The guys who just flat out said it won't work without doing the MATH, should not be considered. The guys who said 2 passes per bay or 3 passes per bay need to prove why that will work.

Tinman

I'll admit there is a risk for the contractor who shares all their MATH. It's rare but I've done it...only to have my design "borrowed" and then "shared" with a lower priced contractor who was then given the job.

ddd

Thanks for all of your advice. We pretty much decided that we are not going to go the copper pipe/fin tube route. Instead of trying to get most of our heat from the floor, we are going to put in base board heaters too. That way our floor will be warm, and the baseboard heaters will do the rest.

Zman

Another option would be to "prepipe" for low temp panel radiators Runtal make a good one.
Do the Math....
Trust the Math...

Tinman

...using pex-al-pex as your pipe.

Tinman

...home-runned

Ironman

ddd said:

Thanks for all of your advice. We pretty much decided that we are not going to go the copper pipe/fin tube route. Instead of trying to get most of our heat from the floor, we are going to put in base board heaters too. That way our floor will be warm, and the baseboard heaters will do the rest.

Please understand that without doing the proper calculations, you're playing an uneducated guessing game in attempting to design a radiant system. You'll get results that correspond.

The best way of transferring heat from tubing is from CONDUCTION, not CONVECTION. That means tubing with plates. Hanging fin tube in joist bays is the worst method proposed and will require water temps that will result in significantly lowered efficiency.

You've come here seeking help and every pro has told you the same thing: proper calculations MUST be done in order to achieve a proper design. Please, take that advice before proceeding. You're gonna spend a lot of money and have to live with this for a long time. Think about it.

hot_rod

Gordy said:

Astro foil is garbage. So I would assume over the top is out of the question? What about radiant ceilings?

Any foil faced surface in a joist bay will get a coating of dust within days and render any reflective qualities unless. I'm not sure there is much foil faced fiberglass around anymore. Even if you find it it has more ink lettering that shinny foil exposed with all the warnings, ratings and instructions they printed on it

I've looked down joist bays years after foil faced batts were installed, hard to even recognize that it was foil faced.

Conduction transfer is what you want. Sound like a floor warming system with supplemental heat may be your path forward.

Gordy

In other words don't depend on any type of reflective insulation, fabric etc to enhance radiants output.

hot_rod

Enhance is a clever way of saying it.

The foil, or even a polished mirror for that matter could never multiply or increase the thermal output from the tube.

The theory was it bounced some of the radiation back up.

But if the R value wasn't enough the thermal energy would take the path of least R, which with a 3" batt was usually the opposite direction of where you needed it.

Plain unfaced batts with plenty of R value, at the very least a 6" batt, would be a better choice over low R foil face.

Smoke and mirrors comes to mind.

Zman

hot rod said:

Enhance is a clever way of saying it.

The foil, or even a polished mirror for that matter could never multiply or increase the thermal output from the tube.

The theory was it bounced some of the radiation back up.

But if the R value wasn't enough the thermal energy would take the path of least R, which with a 3" batt was usually the opposite direction of where you needed it.

Plain unfaced batts with plenty of R value, at the very least a 6" batt, would be a better choice over low R foil face.

Smoke and mirrors comes to mind.

Hot Rod,
I have always felt the value of reflection was very over rated. I hear what you you are saying about dust.
Does that mean there is no value in the air space as well?
This is good stuff.
Carl

Gordy

To me its all about the best heat transfer to the very surface that will heat the space, and we all know that is conduction. Anything else is second best. Convection has its merits as second best with limitations in certain situations speaking soley from a radiant design.

We all know insulation merrily slows heat loss not stop it dead in its tracks, and that the higher the delta between the surface you want to heat, and the surface you don't want to heat the path becomes evident.

One has to ask themselves in a crawl space scenario, would it be cheaper, and easier to skip insulating the floor, and insulate the walls, and rim joist area of the crawl space. Condition the crawl space with base board with the end result being the conditioning of the floors.

Easier being not weaving tubing, and plates on your back, cheaper being base board in lieu of plates, and pex. Supplemental is base board in the conditioned area above because radiant floor is not going to get it. So now mixing becomes unnecessary. Which probably would not be necessary any way with a high temp staple up design.

I guess in a nut shell sometimes no matter how bad you want radiant there comes a time to consider other options instead of trying to make it work with lack luster results.

I know this much if the crawl space is not conditioned, and even though the floors are insulated you still get cold floors. Carpet tempers it, but it's still a noticeable difference.

Alan (California Radiant) Forbes

I'd be interested to see if ANY floor warming (let alone heating) happens with 3" of flooring. It seems like a big expense, but there are people out there that will pay a lot of money just to take the chill off the floor.

Tinman

I've come close. 2 sheets of 3/4" plywood in the subfloor plus a floor covering of 3/4" hardwood. Roughly 8000 sq ft home about 8 years ago. Extruded plates on 8" centers, roughly 118 degree water supply temps. Every wall in the home was 2 x 6 construction. Super tight. They're still my customers, still very happy.

Tinman

I don't remember the exact details but I ran the numbers through the Advanced Design Suite and it said it would work and it did.

Gordy

I wish I had that customers wallet Stephen.

Tinman

Me too

Tinman

I used my one and only Wirsbo 212 Pro Panel on that job. Saved a bit on labor and looks good in the boiler room.

hot_rod

Zman said:

hot rod said:

Enhance is a clever way of saying it.

The foil, or even a polished mirror for that matter could never multiply or increase the thermal output from the tube.

The theory was it bounced some of the radiation back up.

But if the R value wasn't enough the thermal energy would take the path of least R, which with a 3" batt was usually the opposite direction of where you needed it.

Plain unfaced batts with plenty of R value, at the very least a 6" batt, would be a better choice over low R foil face.

Smoke and mirrors comes to mind.

Hot Rod,
I have always felt the value of reflection was very over rated. I hear what you you are saying about dust.
Does that mean there is no value in the air space as well?
This is good stuff.
Carl

Yes you needed the air space with a convection installation, like UltraFin or the Wirsbo suspended tube method.

With transfer plates the insulation could be tight against the plates, or spray foam if you dare. The concept is to heat the air and get it tumbling or turning in the space, with convection currents.

The one issue we had with spray foam it would find any gap between the floor and plate, get in-between, expand and push the plate a bit.

A better method was to cover the plates first and spray foam.
It made it much easier to repair a tube if one got nailed also.

The rubber tube staple up was somewhere in between, not a true convection system, but without transfer plates not a great conduction system. I don't believe the foil backed with a 2" air space added any value for all the above reasons.

hot_rod

Gordy said:

To me its all about the best heat transfer to the very surface that will heat the space, and we all know that is conduction. Anything else is second best. Convection has its merits as second best with limitations in certain situations speaking soley from a radiant design.

We all know insulation merrily slows heat loss not stop it dead in its tracks, and that the higher the delta between the surface you want to heat, and the surface you don't want to heat the path becomes evident.

One has to ask themselves in a crawl space scenario, would it be cheaper, and easier to skip insulating the floor, and insulate the walls, and rim joist area of the crawl space. Condition the crawl space with base board with the end result being the conditioning of the floors.

Easier being not weaving tubing, and plates on your back, cheaper being base board in lieu of plates, and pex. Supplemental is base board in the conditioned area above because radiant floor is not going to get it. So now mixing becomes unnecessary. Which probably would not be necessary any way with a high temp staple up design.

I guess in a nut shell sometimes no matter how bad you want radiant there comes a time to consider other options instead of trying to make it work with lack luster results.

I know this much if the crawl space is not conditioned, and even though the floors are insulated you still get cold floors. Carpet tempers it, but it's still a noticeable difference.

Maybe at that point you just put a furnace in the crawl space and blow hot air, under the home

Worked great when we had to thaw crawlspace home plumbing in the mountains.

California homeowners would build mountain homes like they did in homes CA and leave all the vents into the crawl open all winter. That along with water lines in the outside walls made for a lucrative pipe thawing business

Rich_49

A suspended tube method will never work . Even if you put the same r value insulation against the band joist you still will have most of your heat flowing to the highest Delta T area which would be the end of the joist bays since we can safely say that poutside is colder than inside the house . Whoever the contractor was that thought this was a good idea should not be allowed back in the house . He has no knowledge of how and why energy moves the way it does . Careful also of the old " I did a heat loss calculation ", although better than contractors that don't perform one or have the supplier do it for them ( usually a bad idea ) anyone can enter information into a program , it takes actual knowledge of how heat and energy move to make it right . Be careful . There are many quality designers who know these things and will design a system and specify performance path and equipment for a local contractor to install for a fee . A few of them right here , I suggest that route . Some will even vet the4 contractors in your area to insure you get a capable one .
May we ask why you chose this time to do this , are you renovating , doing repairs in the home ? There are other ways to heat the space and also the floor , sheetrock has little r value to penetrate and energy flows to the coldest surfaces . Radiant ceilings also warm floors . 70* floors in Colorado for instance using radiant ceilings .

icesailor

Gordy said:

Astro foil is garbage. So I would assume over the top is out of the question? What about radiant ceilings?

Astro foil is more than garbage. Its crap on a roll.

Contact the company and have them send you proof of their peer reviewed testing and ASTM/UL ratings of the reflective and resistance values of their product. I was admiring rolls of that stuff at Lowes last week. The R/Radiant reflective value was a WAG, and the resistive value was non-existent.

Staple it up under floors. Great idea. Gives the mice a larger area to get around on and find ways into the buildings when someone cuts out a odd shaped 5" hole to put a 3" pipe.

Just like all flex duct and flex duct board, Gives the rodents full access to the inside of houses. Including squirrels.

Rich_49

Better yet . Look up the federal trade commission's findings on their claims .

RobG

Have you looked into Warmboard? It installs on top of the subfloor and will give much better response times. Where are you located? Maybe we know someone in your area who is qualified.