Look at these numbers; am I crazy to think something is wrong???

Brent_2

I'm not sure why you are so worried about supply temp. The spacing and flooring is already decided. If it turns out you don't need as high of temp you can just set your controller lower. Maybe you can make 1 temp lower or both or neither.

dblagent007

Water temp design

I am building a three story house (basement, main, and second floor), all of which will be heated with radiant heat. The tubing is in concrete in the basement and is in Warmboard on the main and second floor.

The radiant contractor designed the system to run at two water temps, 113 F and 139 F. The entire main floor was designed to operate at 139 F and the upstairs and basement, with the exception of only one room, were designed to run at 113.

My home is highly insulated as follows:
walls = four inches of closed cell spray foam (R28);
underside of roof = six inches of closed cell spray foam (R42) with another six inches of an unfaced fiberglass bat (R18);
floors = two inches of blueboard (R10) under concrete slab, eleven inches of blown in fiberglass under the Warmboard on the main floor and the second floor (R25-28).

Given that I am using Warmboard and my home is highly insulated, why does my radiant system require such high water temps? My home looks more or less like a rectangle. I don't have any rooms that stick out in a weird direction. I've attached the water temp design for each room as well as the heat load calcs for the two rooms with the highest heat loss. In fact, I have even attached the floor plan in case that is off interest to you. Take a look and tell me what you think.

I should note that the highest design temp room (the mud room) was spec'd as if it had carpet on it when in reality it will have tile. I think that the next highest temp room (the nursery) is off because the amount of insulation under the floor was shown much too low.

The weird thing about this is that one of the reasons that I chose Warmboard was because so many people on the Internet were raving about how low you can get your water temps. However, the radiant contractor is blaming the high water temps on the Warmboard because the tubing is only twelve inches on center. The contractor says that if he would have designed the home upfront (he was brought in after the Warmboard was put down), he would have used gypcrete and spaced the tubing closer together in higher heat load rooms to get lower water temperatures.

I think the real problem is that my radiant contractor is treating the Warmboard the same as if it was twelve inch on center gypcrete. If you open the attached file with the radiant design you will see that he has treated the Warmboard areas as "lightweight overpour."

The radiant contractor has never used Warmboard before (very very few have in my part of the country; gypcrete rules here) so I don't think he is giving it any credit for being more efficient. If the Warmboard should be treated differently, then how should he change it in his program?

I would appreciate your thoughts on this.

Bob Bona_4

first

thoughts are that infiltration and fenestrations in a particular room are going to dictate water temps in it. You are dealing with fixed centers, so supply temps are your only means of control. Where you might evision 120 degree supply temps could end up being higher b/c extenuating circumstances such as floor coverings or heat losses.

Most software I know of doesn't take WB into acount, so your contractor may have opted to use gyp as a similar emitter. As you know,the dynamics of the two are different. My gut is to trust WB design criteria from the factory. I have dealt with them, and they are really sharp.

dblagent007

I have attached Warmboard's water temp design chart. Now, let's assume that the radiant contractor did the heat load calcs correctly. The highest calc'd room load per ft2 is 16.3 with a floor covering R-value of 2.2. This is wrong because he figured the room would use carpet when it actually uses tile. However, let's use it as a worst case scenario example.

If I use the attached Warmboard chart to set the water temps, then my max water temp is 115 F.

Paul Pollets

Water temps and modulation

Before 2nd guessing the contractor, let's presume the calcs are 'close'. The concrete slab temps of 113 seem high, unless you live in Northern Minnesota. Most slabs I design require 80-95 degrees req water temp. Were the calcs performed on radiant software? Were the correct insulation values entered for the building envelope?

Using a modulating condensing boiler, the heating curve would simply be set lower to reduce water temps in the heating circuit(s).

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dblagent007

The design temp where I live is 5 F. The calcs were performed with Wirsbo software. The insulation values for the envelope of the house (the outside walls, underside of roof) were entered correctly. You can see those values on the calcs I posted above.

The problem I have is that the system is already in. It has a mixing valve set at 113 F. As I mentioned in a post above, the highest water temp dictated by Warmboard's chart is 116 F. I suppose I can lower the heat curve to set the max temp at 116 F, but then my system has a mixing valve that is doing absolutely nothing.

EDIT: Paul, the tubing is twelve inch on center in the conrete and the floor coverings will most likely be carpet.

EDIT #2: Actually, now that I think about it, the insulation value under the concrete was only set at R5 when it should have been R10.

dblagent007

The plot thickens

After I found the Warmboard water temp chart, I called Warmboard. The guy at Warmboard agreed that if I used their water temp chart, my max water temp would be 116 F.

I reviewed the calcs I posted above with the Warmboard guy and he said that if the contractor should have approximated Warmboard as six inch on center Concrete (not twelve inch on center gypcrete).

It is starting to look like my initial suspicions were correct. The contractor didn't give Warmboard any efficiency benefit. Approximating Warmboard as twelve inch on center gypcrete in his software program results in ridiculously high water temps.

dblagent007

The plot thickens even more

Okay, so I called my radiant contractor and told him about the water temp chart provided by Warmboard. At that point, he started to question the delta T and pump flow rates that Warmboard assumed to come up with the chart.

At this point, I have no idea who is right or what to do. All I know is that I have never, never heard of a Warmboard system requiring 140 F water with a home that is as insulated as mine and in a climate that has a 5 F design temp. Something is very wrong here and I need to get to the bottom of it.

jp_2

btu/sqft

what are the required btu/sqft?

how long are the loops?

dblagent007

The BTUs/ft2 for all of the zones are shown on the design (the PDF file I attached above). The highest BTU/ft2 shown on the design is 16.3, but that will drop once the insulation values have been revised. In the end, I think the room with the highest BTU/ft2 will be around 14-15 BTUs/ft2.

heatboy_2

It looks to me ....

.... that two rooms, the mudroom and nursery are the rooms that need 139° water. Everything else is substantially less. What is it about those two rooms that make the load higher?

Ron Gillen

Heatloss Calcs

Check the ceiling and floor calculations for the individual rooms. Nursery shows downward losses. Even if the floor is not insulated there are no losses up or down if above or below a heated space. If this was done for all rooms it would make a huge difference in the reported heat load.

jp_2

zones

might be too late, but I would have put all bathrooms on one zone. often a warm bathroom in cool weather is nice, bedrooms can easily be cooler, even tieing in the kitchen would be a good idea. wake up, pee, shower go make coffee. or make coffee first!

dblagent007

Bedroom below nursery

Good point, there is another bedroom directly below the nursery.

Above the nursery is a little more complicated. The roof line comes right down to the outside walls of the nursery. We have insulated the underside of the roof as it extends upward from the outside walls of the nursery. Once the roof comes up high enough there is another room with radiant heat in it above the nursery.

In the end, all of the space above the nursery is considered to be within the conditioned envelope of the house. Part of the area above the nursery will actually be heated with radiant and the other part (pony wall areas) will not be actively heated, but will be inside the insulation envelope so that they are only a few degrees cooler than the heated area.

dblagent007

Actually, it's not too late.

One thing I like about this contractor is that he is running thermostat wires to every room so that we have the option in the future of making every room it's own zone. All we have to do is find the thermostat wire in the wall, hook up a zone valve at the manifold, hook up the thermostat wires at the manifold and in the mechanical room and, viola, I have a new zone.

Of course, this only works if the tubing loops in that room only extend through that room (i.e., can't have tubing loops running under walls between different rooms). In my house, the tubing loops are such that I really could make each room a zone if I wanted to.