Radiant problems, Please HELP#2

Tom Towne

Hello All

I figured I should make a second thread on this one as it is getting long and my last post has a important question to all who are willing and able to answer. Here is the last post

Duncan

Thanks for the very informative post. I too question the bubble wrap. I need to ask him about this again. He said that his radiant program does not have a calculation for 7/8 tubing at 16OC but his estimate is that the floor only has a potential for about 13,000 btu at around 130deg water temps. Can you or anyone else confirm this. Another local contractor feels that 1/2 PEX run 8in OC should be added to the system that is already in place. The first feels that this bubble wrap will get the floor where it should be which is still only 13,000 BTU. Both are in agreement that the origonal set-up of 7/8 16OC would never heat the house to 70deg. Kind of confused. Also my contractor can not get a hold of a Munchkin for 4-6 weeks. I did a very good search on the internet for companys that have them in stock. The ones that do are charging 20-30% and one even 50%above list price. Contractor says it is ridiculous and to hang in there as he will locate one. Who ever said heating was easy? Thanks again.

heatboy

If you were close to me..........

I would have said the same thing. Leave the tubing you have alone and add some extruded plates and either 3/8 or 1/2 tube. Provided the tubing installed now runs down the center of the joist, there will be plenty of room to add two more runs of tubing per bay. Water temperatures will reduce greatly be doing this.

Dump the bubble wrap and stick R-19 or greater right up against the sub-floor. Using the extruded plates is, quite possible, the only thing that will save your project.

You aren't close to the Lehigh Valley, PA area, are you?

hb

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Mark Hunt

Tom


I do not think anyone has a software program that will calculate 7/8" tubing 16" oc. That particular design is pretty much the child of the i-net company.

The bubble insulation does not have the same R-value as what you currently have, so I would not recommend replacing it.

Adding 1/2" tubing will improve the system. If you look at what EVERY other MANUFACTURER of tubing does, you will not find 7/8" or 3/4" listed as an under-floor option.

A REAL heat-loss needs to be done, if one hasn't already.

As for the Munchkin, I would have the contractor contact HTP directly and see if they can help.

What size do you need, and where do you need it?

I hope that everything works out for you sir, I am sorry that you have had to go through this.

I would REALLY like to hear what the i-net company had to say about all of this. Perhaps your sharing will save others from the experience.

Mark H



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Tom Towne

Hello Guys

Heat loss analysis showed 39,000 btu with design conditions of -10deg> I have other info if needed. What would the potential BTU of a 28X36 floor with 1/2 pex at 8in O.C. with 130deg temps. Thanks.

Dave_16

Water Temps

Okay here it a little infor that may help you.

Floor R-Value .05 130 Degree Water Temp Btu's SqFt = 33
Floor R-Value 1.0 130 Degree Water Temp Btu's SqFt = 27
Floor R-Value 1.5 130 Degree Water Temp Btu's SqFt = 23
Floor R-Value 2.0 130 Degree Water Temp Btu's SqFt = 20
Floor R-Value 2.5 130 Degree Water Temp Btu's SqFt = 17
Floor R-Value 3.0 130 Degree Water Temp Btu's SqFt = 16
Floor R-Value 3.5 130 Degree Water Temp Btu's SqFt = 14
Floor R-Value 4.0 130 Degree Water Temp Btu's SqFt = 12

This is 8" PC with Radiant Trak/Joist Trak.

Tom Towne

Thanks Radiantwizard

jp_2

real time data

well then, what does the program say for 25F outside with 150F water temp(your current situation)? what is the expected room temp compared to the present room temp?
if the contractor says the floor potential is only 13Kbtu's and you need 39kbtu's, bubble wrap is not going to get you there either will insulating the bond. you need to take a close look at what is presently happening with the system.

I agree with more tubing.

what is your pump flow rate?

jp

Tom Towne

JP

The pump is a Bell & Gossett NBF-12U. Radiantec says .5GPM for every 100ft of tubing. I just looked back in my files and there is a page that said this system would produce up to 40,000BTU/hour. Not even close.

Duncan_9

Output and possible fixes.

Tom, 1000 square feet of heated floor area at 13 btu/sq.ft. output gives you 13,000 btu/hr total output.

A system with suspended 1/2" tubing on 8" centers, no plates, 130°F water temperature running at a 10°F differential (supply temp minus return temp), no plates, and a floor covering with an R value of 1.0 over a well-insulated 3/4" plywood subfloor will give you about 13 btu/sq. ft. output. This is according to Wirsbo's Complete Design Assistance Manual.

I don't think it's too much of a stretch to consider this roughly similar to your system, depending on your floor coverings. This ignores the so-called plates. Others may disagree, but without expensive engineering computer modeling of a 7/8" tubing system, this may be as close as you're gonna get for an output estimate.

But for a floor covering R value of 1.0, forget about carpet and pad.

Which brings me to another point. It appears I wasn't paying close enough attention to what you said, and I misunderstood your construction.

You have a full basement? Is the ceiling finished? Are the floors finished?

At this point there's only a couple things to try to see if the existing system can deliver comfort.

You said: "After heater is done cycling on the temps go out at 150deg and then back in at 143 when the return gets down to 125 the heater comes back on."

This tells me you have a 7°F SYSTEM differential temperature across the tubing in the floors at the 150°F delivery temperature. Not bad. Less output will occur at lower water temperatures.

Now let's look at your average water temperature the water heater produces and delivers to the tubing.

Your water heater has roughly a 25° differential. The water temperature goes down to 125°F before the burner comes back on to heat the water. It shuts off when it gets to 150°F. That's a 137.5°F average water temperature.

With floor tubing temperature dropping 7°F across the tubing, the 137.5°F average water temperature is probably strung out over a fair amount of time since the heater temp ranges from 125° to 150°.

If you could tighten the differential using a digital control, you could raise the average water temperature delivered to the system, and therefore the btu/sq.ft. output. The charts I mentioned previously show about an 18 btu/sq.ft. output for 150°F average water temperature for the construction mentioned.

155°F off and 145°F on at the water heater corresponds to a 150°F average water temperature. IMPORTANT! What is the maximum recommended water temperature the tubing can handle? This is not a viable approach if the tubing can't handle these temperatures!

Increasing flow to tighten the differential temperature across the tubing in the floor would result in marginal btu/sq.ft. gains, a couple btu/sq.ft. Not even that if you take floor R value into account.

However, all this is pretty much wishful thinking. I imagine your finish flooring is well over an R value of 1.0, so in reality, you're not going to see the kind of increase in output I mentioned.

Your repair approach depends on what phase of construction you're in. Here's what I would do if I were you.

Lower your heat loss by going over infiltration and exfiltration with a fine tooth comb. Seal ends of joist spaces, and possibly even the log chinking. ESPECIALLY at corners where logs cross. Inside and out! Non-expanding foam at all electrical and plumbing penetrations and sill plates is also very effective.

Are floor coverings installed? Go with the absolute lowest R value coverings you can find.

Bumping up the heater average water temperature by tightening the differential could result in some gains. Not a realistic long-term option if short-cycling of the heater results. Most likely not an issue with a modulating boiler.

Unfortunately, I suspect these repairs may not get you there if your home only gets to 62° at an outside temperature of 25°, and your design temperature is -10°.

After these fixes I'd be looking at adding more heat.

Least invasive, highest operating cost, highest anger and aggravation factor: small electric heaters in each room for supplemental heat.

Absolutely the best comfort, but most invasive and possibly highest cost: add plates and tubing. Relax and enjoy the heat happily ever after. Are radiant ceilings an option?

Fairly invasive, fairly costly, and extremely comfortable: leave existing tubing for floor tempering, and add panel radiators for low temperature, comfortable radiant panel heating.

Tell us what phase of construction the home is in. Sheetrocked? Wired? Floors finished?

Sorry about the length of this post. Way too long-winded!