BTU gain from \"suspended joist\" radiant to\"staple up\" radiant???

Unknown

not 3 or 4 times the entire system price, but for this section of the system, it could be.

DeirdreLouisville_2

BTU gain changing suspended joist radiant to staple up w/plates?

Dear Wallies,

Some of you may remember me from last year. I have an circa 1882 stucco over solid brick home. Last year, we had radiant floor heat installed on the first floor.

Unfortunately, they used the "suspended joist" system-- they ran 1/2" pex suspended about 4" below the subfloor. Several inches below that, they installed "reflectix" and then installed R19 fiberglass below that. Lots of money, lots of intall time, lots of problems from day one-The biggest one being that the rooms can't get above about 60 degrees when it is really cold out. Contractor and Zurn rep say the system puts out 20 btus per sq. foot.

Before you ask, no they didn't do a heat loss calculation AT ALL, simply went on the Zurn rep's guess-- The house is in an historic ditrict and has large single pane windows and twelve foot ceilings.

This last year I replaced my old boiler with a Lochinivar Knight (80,000) and installed radiant in the kitchen and two baths (pex in lightweight concrete). Used a different contractor, of course. Kitchen and baths heat well.
So, here is my question- If I have the suspended pex reinstalled as staple up with plates, how much additional heat would be delivered to the space? Would additional insulation below the floor make a significant difference?
Thanks for any advice you can offer!
Deirdre

jp_2

i think,

everyone will ask you, "how much heat do you need", in other words, do a heatloss, you can get a copy of Slantfin's software on the main 'wall' page. heavy plates will surely help by the way.

DeirdreLouisville_2

I have looked at the product, but frankly, I am just a middle aged, barely computer literate woman doing a home renovation-- I don't want to install a new program and learn to use it! Last year, I did some quickie estimate at an interactive website and I think it was in the 30 btu sq. foot range.

Troy_3

Floor makeup?

What is the makeup of your floor? Including finish flooring. 30BTUs/sq.ft. from 1/2" pex and extruded aluminum plates is doable depending on how thick your floor is. I usually figure twice the output when adding extruded plates over bare tube. When you say only 60deg. inside, at what outdoor temp. is that? Do you find at 10 deg. warmer outside it is warmer inside?

DeirdreLouisville_2

The floor is 100yr. old oak on top of a subfloor of 120 year old pine boards. It has been refinished at least twice, losing a bit of thickness from sanding each time.

zeke

I would be curious to know what the surface temperature of the floor is. It looks like a poor design since heat would have to radiate and convect to the underside of the subfloor, then conduct thru 2 floors and finaly radiate to the room, the worst scenario. I think you were badly served by the contractor by not knowing the heat load before tackling such an expensive job.


If you could measure the temp of the floor surface, then a good rule of thumb is that the BTU's per sq foot that it will deliver is about twice the difference in temps between the floor and the desired room temperature.


For example, if the required room temp is 70 degrees and the floor temp is 100, then you would be getting 2x(100-70)=60 BTUH per square foot.


If you give us the outside temperature at which this monster gives you only 60 degrees, I think we can estimate the load right now and determine whether you want to throw good money after bad to correct it or use it with some auxiliary heat source.

Unknown

Well, Deirdre, a brick home with single pane windows, high ceilings, and no insulation can *very easily* outstrip any radiant floor method.

Luckily, your climate is not extreme. But before you spend a bunch of money on aluminum plates that *might* fix your problem, have someone do a real load calculation. Otherwise, we're all guessing like your zurn rep, and you can spend a lot more money on a solution that may not solve your issue.

DeirdreLouisville_2

If the outside temperature is say, 20-25 degrees, my living room and hall cannot get above 61. The dining room, which is adjacent to the heating kitchen and heated bedroom and which has only one short wall exposed to the outdoors can get to about 63 degrees.

Spudwrench

add panel radiators?

After doing a heat loss, you might consider having some European style panel radiators installed as supplemental heat. They are fairly slim and unobtrusive and if you're just using them to suppliment the existing radiant system, they could probably be pretty small. It would save a lot of labor compared to ripping out the existing insulation, radiant tubing etc- you'd still have your nice warm floors, but you could also have a nice warm room!

good luck,
Nathan

jp_2

i agree with spud

get a heatloss done and look at adding some panel radiators with TRVs. properly RE-done floor radiant would probably cost 3 - 4 times more than it did.

zeke

The design heat load as I calculate should have been twice as much as you are getting, based on a zero degree outside temp and 70 deg inside or a differential of 70 degrees. Presently you are getting a 40 degree differential (60-20) which means that the required heat is 70/40 times what is being delivered.

I doubt that an improved floor radiant system can deliver what you need not to mention the cost.

Accordingly, I concur with the above people that you can go to paneling at a good deal higher temperature to get the increased heating you need and by all means don't use anybody that doesn't give you a detailed estimate of the heat losses for a 0 degree day.

As another option, you might consider a hot water radiator that could take up the added requirement. The Europeans make some nice looking units that could do it.

Kevin_in_Denver_2

fan coil

The least expensive method would be to add a fan coil. I have one in my uninsulated office and it operates just like one more zone.

Again, heat loss and sizing calculations apply.

DeirdreLouisville_2

Panel radiators would not be period appropriate in my house. Putting back in the period radiators we removed is impossible as they have been scrapped (huge, very heavy iron). We have a final payment to the original contractors of about $4400 (at the end of last winter, they were still tweaking the system and offered to wait for final payment until this winter, assuming the system performed adequately).


The area we are talking about is about 700 square feet. Would it really be that expensive to take down the insulation and add plates to the existing pex (there is some slack and the run back to the boiler is 15 feet-- could additional pex be spliced in, there?) and then reinsulate?


Researching around the links here at heating help, I ran into a study that showed a doubling of btu between staple up with no plates vs. staple up with plates. I didn't find any btu information on suspended joist systems, but is reasonable to expect roughly the same doubling of btu delivery?

Troy_3

plates

I would add plates. No question. What is your coldest outdoor temp? Where are you located?

DeirdreLouisville_2

3 or 4 times more??

I know you don't normally talk price, but is it really true that a proper installation of 700 square feet of radiant (hooked up to existing boiler) would be $34,000-$45,000?

DeirdreLouisville_2

We are in Louisville, KY. I understand my local design temp is 5 degrees. But, we don't spend more than a few hours a year at that temp. We are willing to compromise a bit, with a system that would keep us at, say 68 degrees on a 10 degree day rather than 70 degrees on a 5 degree day.

The house is very large and we can always retreat to other rooms for a few hours/days a year.

Unknown

No Question?

What if adding plates doesn't solve the problem? Then what have you achieved?

DeirdreLouisville_2

Well, that's why I am here asking was sort of improvement I might expect from adding the plates

If, as some of the research I have looked at seems to suggest, I can double the output with the plates, then I think my problem will be solved (at least to a point where we could be happy with it). If, on the other hand, plates will only give me a 10-20% improvement in heat delivery, it may not be worth the expense.

The house is very poorly suited to forced air (high ceilings, 3 stories with an open staircase). We still have envelope improvements to make, which may reduce our load in the future.

Our biggest handicap is location--Here in Louisville, NO ONE that I have ever spoken to will do a "Manual J" heat loss calculation (or any other explainable method of deciding how much heat is needed). Instead, boiler guys will add up the number or radiators and HVAC guys give a guess based on square footage.

Unknown

You think. But you don't know. No offense, but you really don't know. Now if you do envelope improvements AND add plates, that may do the trick.. but again, neither you nor any of us KNOW until those numbers are run.

you could expect 50% to 100% more heat from heavy plates, depending on how hard you can push your flooring which is also a limiting factor.

But, that does not mean it'll do the trick. Will it help? definitely. But it does not mean that it will solve the problem.

jackchips_2

It will also

be interesting how this house will be portrayed if/when it is ever sold.

For sale: One house that may or may not reach design temp but there are plenty of rooms to gather in to hug.

:-))

Jack

Troy_3

Heatloss

Calculations is nothing more than an educated guess. I have seen more people say that if you do a heat loss after the fact you will see why it doesn't heat. I never got this logic. Reality is here. The lady is living with this system. We have real life conditions to observe. To tweak a heat loss calculation will not get her more heat. It is nothing but a tool. It is much more effective to see what is happening at various temp. Now the next step is to look at the system- available total btus, loop lengths of installed tube, boiler pipe size, pump size etc. I feel you will be real close from what little we know. The system realy needs to be checked.

Unknown

You are correct. Done correctly though, they are pretty close, and could much more quickly than any other alternative determine whether it's even worth thinking about putting plates in, or whether more severe actions are necessary.

Just throwing in extruded plates blind could potentially be quite a waste of money if it's still not even close, which is quite possible in this case.

DeirdreLouisville_2

Rob, you are right, I don't know. And, as far as I can determine, there is no one locally that I can hire to come and tell me either a)how much heat I really need or b) how to design a system that will deliver radiant heat.

I am very envious of the set up so many seem to have where actually qualified, interested radiant heat proffessionals will come to their home, design a system, install it and ta-da! They get actual heat! All I can do is the best I can-- that is research well and then guide my local guys (not incompetent, just stuck in their ways or unwilling to research)to do what can be done.

As to how the house will sell--Who knows? It is 6,000 square feet, three stories high and situated in an historic landmark district. The second and third floors are heated/cooled via forced air, ducted out of the ceilings (previous owner put in in 1994). When we really want to get warm, we climb a ladder on the third floor

When we bought the house, the first floor was heated by an ancient gravity fed boiler with a 300,000 btu capacity. It also had no insulation whatsoever, ancient, leaky, huge windows and a million other repair issues to tend to.

We have blown R38 into the attic, insulated the few frame walls in to R19 (the remainder are 11" thick brick), put interior storms on half of the 65 windows and used 144 tubes of caulk around the window openings.

Between the new boiler, the 600 square feet of radiant in concrete and the 700 square feet of suspended joist radiant, we are in over $25,000 just for heat, on just one floor of our home. If spending another few thousand will get it right, I can do that. But I hate to just give up and start over.

Ed_26

radiant

What about your ceilings? - 12' ceiling, if not a special finish, could you put supplemental radiant there? The advantage is... run @ higher temps/fast response. (or wall radiant) How thick is the floor? (100yr. oak, 120 yr. pine is probably 3" or better.) With the addition of plates underfloor, should do the job. (perhaps injection mixed to acheive nec. temps to loops?)

DeirdreLouisville_2

The ceilings are ornate plasterwork, so no we would consider touching them-- but the floors are only about 1.5" thick-- the pineboards are the only subfloor and the oak has been refinished at least twice and is no more than 1/2" thick.