Design help / advice

ben01

Hello all,

I am currently in the process of a home remodel with a room addition. The house is 110 years old and has cast iron radiators throughout, with the exception of the kitchen, family, and mudroom addition. The kitchen large radiator was removed for lay out, the living room was a addition 30 years ago where the utilized forced air, and mud is new construction. Anyhow, I am looking to utilize radiant heat under the 3/4" X 2-1/4" oak which rests on 3/4" plywood. i have run a room load calculation with Uponor's ADS which came back with a heat loss of 29,500 over 1,360 sq foot. I'm in Chicago and selected average construction and have all the measurements correct. In your experience, how accurate is this program?

I am planning on using a cast iron boiler with a separate mixed zone for the floor heat and keeping the original cast radiators in the remainder of the house. My major concern is will this be enough to properly heat the area? much of it is a open concept with no walls separating. We do have quite a bit of glass, which was accounted for. All windows are new Marvin and entire area will have R-21 closed cell spray foam insulation.

Curious on the pros thoughts?


Thanks in advance!
Ben

ben01

Alos, planning on using 1/2" tubing with 6" spacing and heat transfer plates.

hot_rod

Looks like 22 btu/ sq foot? that is workable if that is actual exposed kitchen floor area. You would need to subtract out any floor square footage that has cabinets or appliances covering the floor, as you will not get much output if any from those areas.

So take that load number 29,500 and divide it by available square footage in the space, the result is the btu/ square foot that you need.

3/4 ply and 3/4 hardwood works out to about R-1.8, so supply temperature needs to be adjusted to accommodate that.

I think that program spits out a design also, showing you required SWT, output, spacing etc?

With an 82° floor surface temperature you get about 24 btu/ sq for in a 70° air temperature, SWT around 118°F.

The RPA RadPad "old school" slide rule is handy for quick calcs.

ben01

Here is a breakdown for the kitchen. I have a living room, mudroom, and powder room too.

kitchen 322 actual square foot
deduct 80 sq ft for cabinets and island
heat loss 5,480
SWT 115



I used the R value of 1.65 in the calculation.

The system shows a radiant load of 30,000 btu / hour.

30,000 Btu divided by 1280 square foot minus cabinets = 23.43 btu per square foot.

I selected 6" spacing.

My major concern is the couple times a year when temps drop drastic. Design temp was -1

thanks

Gordy

For Chicago design temp ranges from 2 to -4 degrees depending on location. I’d use -4 as that’s a sure thing most winters around here.

Radiant ceilings is a fine option also. Not so much dependent on available floor space unless there is soffits for the upper cabinets in the kitchen. Which still gives more sf than base cabinets. Also the r value of the floor detail is not a factor in raising supply temps. You could even have both floors, and ceilings.

I think 22-24 btus a sf for new construction is a bit high. Usually heat loss calculators are padded for a very good reason.

Gordy

R 1.65 is close for the floor. R values for soft, and hardwoods vary some what depending on information source. Figuring high is better than low.

ben01

the kitchen and family rooms are existing construction but have and or will be buttoned up. Rim joists were spray foamed, walls were sprayed, and 2nd floor roof deck above is also sprayed. I know nothing about radiant ceilings.

Mudroom also has a open staircase to basement. I plan on installing a loop in that slab, as it is still open.

What would be considered "reasonable" btu per square foot?

hot_rod

Radiant panel output is pretty close to 2 BTU/ square foot for every degree difference. Temperature difference between floor surface and air temperature.

So if the room temperature is 70F and the entire floor is running 82 82-70= 12 X 2=m 24. That is where that22- 24 BTU/ sq ft number comes from for a comfortable radiant floor.

82F floor surface is considered comfortable for bare feet on radiant floors. Above that some folks experience sweating feet
Shops or commercial radiant can run a bit higher if occupants are never bare footing Robert Bean has some studies on floor surface temperature and occupant comfort at healthyheating.com

So for more output either raise the floor surface temperature, or lower the room air temperature.

Back in the day radiant was promoted as being able to supply a comfortable home at lower air temperatures, say 67 or 68F. I don't find that to be true, especially with older folks. My mother in law needs 72- 73 F these days to be comfortable.

As Gordy mentioned ceilings and walls can have higher output due to both high possible surface temperature, and very little furniture and cabinets up there.

Run a ceiling at 88F surface temperature in a 70 ambient 88-70= 18X2 = 36 btu/ sq ft possible.

I'd guess 5-10% fudge factor in any of the load calc programs?

Gordy

I’ve never found that lower room temp claim because it’s radiant to be true either. I always like 72

May have been because the envelopes were looser back then, and the floors temps never really dropped to near set point.

The fudge factors on these programs can be variable when compared to real life conditions. If the wind speed is more than the program uses that factor narrows considerably. If the winds are calm then it becomes more padded. Solar gain internal gains all can create variable factors. The program has a base set of conditions that the program writer feels comfortable with.

hot_rod

Yeah, the heat load number is basically a snapshot in time, conditions inside and out can and do change second by second.

In the solar thermal business they call that the instantaneous heat output when they rate and list themal collectors.

But you need a starting point, so it is what it is.

ben01

Are others using the Uponor ADS? if not, are there any other heat loss calculators that could be could recommended?

hot_rod

You probably need some training and experience with a powerful program like that, does it have a tutorial? Or someone familiar with the program to check your work.

A radiant specific software like that is best. Several fairly simple free online calculators at SlantFin and US boiler websites.

ben01

Any input on the generic transfer plates found on Ebay and other sites?

Zman

ben01 said:

Any input on the generic transfer plates found on Ebay and other sites?

What is the application?

ben01

I am looking to utilize radiant heat under the 3/4" X 2-1/4" oak which rests on 3/4" plywood.

Gordy

Extruded omega style plates offer the best heat transfer.

Conduction is king. If the tube fits loosely in the channel, and the plate doesn’t make good contact to the floor underside. No good.

hot_rod

Radiant Design up in Bozeman, they were the original designer of the extruded plates, might find some good info at their site,

3/4 hardwood and 3/4 softwood =- R-1.8, add any floor covering r-value to that.

https://radiantdesignandsupply.com

ben01

Thanks, I looked into the plates from Radiant Design seem to be the ticket but pricey.

I am having quite a hard time figuring out a heat loss for the house. Its 100 + years old and has had several improvements in the past years. The entire attic has spray foam as do many of the walls, which were opened during remodeling. New windows were installed throughout too. Doing reverse math from the omiters in the existing portion of the house, the system was designed to have 60 BTU / sq foot. Of the 3 programs I used, im coming back with 21-27 BTU / sq foot.

I had my heating only supplier run the heat loss and he simply used 30 as a "standard" multiplier for each room.

Gordy

You are probably 20 a sf. Maybe less. It’s good the emitters are over sized.

Good plates are not cheap, but like insulation it’s the gift that keeps on giving once installed correctly. With your floor detail you need good conductive heat transfer so make sure plates make good floor contact.