Radiant panels and runtal baseboards on same zone

mb_il

I have a room above my garage that is currently unheated. Heat loss calculations show I need 12k BTUs to cover the ~350 square foot room (garage below, attic above, 2 windows & 3 exterior walls). Looking to get insights on the best way to combine Roth radiant panels and Runtal hot water baseboards being fed from the same supply/return.

• expect to get ~18 BTUs / square foot with the Roth, so that gets me about halfway there (6.1k BTUs)
• looking to put in two 96" Runtal UF-2 baseboards (https://www.supplyhouse.com/Runtal-UF-2-96-8-ft-UF-2-Baseboard-Radiator) & one 72" UF-2 to augment. According to the below, I can expect to get 350 BTUs/ ft at 140F, but don't expect to fully get this given supply is coming in 110-120 degrees. Assuming for the moment 250 BTU / sq ft instead, so 250 * 22 = 5.5k BTUs. Planning to install on opposite ends of the room against exterior walls.

https://runtalnorthamerica.com/wp-content/uploads/2020/02/Contractor-Series.pdf?srsltid=AfmBOors1-vkOZTW-_-u23ecuqj9EsvLhRvZYrAfDNSM9haTic_QZfVI

A couple of questions:

• what is the best way to design the layout of the loops? The room is fed from a manifold in the wall of the garage. Initial thought is to put each radiator on it's own loop from the manifold, and then have three separate loops to cover the Roth panels (limiting the loop length to ~200 ft each) for a total of 6 loops. Probably would have a distance of 25-30 feet from each 96" Runtal to and from the manifold, and no more than 5-10 feet for the 72" Runtal.
• can Runtals be fed directly from Pex? All the images I see online shows them connecting directly to copper. What are the options here? Would like to try and run the supply and return loop to the Runtal through the Roth panels themselves, again on their own loops.
• Any issues with 110 degree water feeding the Runtals? Their website says temperatures as low as 140F, but I've also seen commentary on various forums that the lower the temperature, the more efficient they are. I haven't been able to find the output chart that shows how the BTUs vary by SWT, hence the assumption of 250 BTU / ft above.
• Room will have it's own thermostat to control for the extra output needed versus adjacent master bedroom / bathroom.
• Anything else I need to worry about? I'm a homeowner who has just done a fair amount of research so a little out of my depth.

Thanks in advance.

Mike

hot_rod

12K load for 350 sq ft sounds awful high? That is about 34 BTU/ sq ft.

Is there no insulation between the garage and room above? A load 20- 25 btu is even a high number for an insulated space.

mb_il

Thanks for the reply. There is insulation, I opened up the subfloor earlier to double check and it’s those big pink rolls of fiberglass insulation in between the garage and this room. I’m assuming there is insulation in the walls as well.

I was under the impression I might need some extra BTUs due to the partially conditioned garage below: we have a heater in the garage and typically keep it around 40-45F in the winter. Not sure if this is useful at all, but some of the recent cold days (0-10F) we’ve had in Chicago the thermometer I have in the room has read 28-30F.

I just don’t want to go through the hassle and expense of fixing this only for whatever I decide on not to end up being enough to keep the room warm. If it’s a little chilly on those 5-10 super cold days a year we get, I’m alright with that.

hot_rod

The warmer the garage, the lower the heat load for the space above. It the garage were always at outdoor temperature in your area the load would be higher.

The load calculation needs to know the space below is 30 degrees, not the 0 design day temperature. So I still believe your load number is way too high.

It's possible the floor alone can heat the space without supplemental heat. You need an accurate heat load number to know that.

mb_il

Thanks hot_rod. Using the various heat loss calculators available freely online, I get a different number depending on which one I use.

Playing around with this one specifically: https://www.omnicalculator.com/construction/heat-loss

Input values:

• length: 30ft
• width: 11 ft
• height: 7.5 ft (sloped ceiling that peaks at 9ft and drops to 4ft before hitting a knee wall
• level: top floor
• insulation: mediocre insulation showed U-value of 0.6, well insulated show a U-value of 1.0. I used a custom U-value of 0.8 as I would probably classify it as somewhere in between.
• 3 external walls, 2 windows

Now, keeping the internal target temperature to 70 F:

• if I set the design day / ambient temperature to -5 F, I show ~8.5k BTUs required (25 BTUs / sq ft)
• if I set the design day temperature to 10 F (conservatively blending the ~40F internal temperature of the garage and the outside), I come up up with ~6.7k BTUs (19.7 BTUs / sq ft)
• if I set the design day temperature to 20 F (more liberally blending the garage and outside), I come up with 5.6k BTUs (16.5 BTUs / sq ft)
• Again, the ambient temperature of the room itself (the room, not the garage below) was ~28 F during the day without any heat on some of the coldest days we've had recently. Probably slightly colder overnight.

So, the floor alone could cover it assuming I can get 17 BTUs / sq ft from the radiant. If I can get expect to get more than that (low/mid 20s), I'd feel comfortable dropping the idea of the runtals and sticking to the radiant floor only.

EBEBRATT-Ed

Rooms over garages ten to be difficult to heat. Basically floors, ceilings and most walls are exposed. but the heat loss should reflect this.

The problem is that a typical garage if not heated the floor has more heat loss than a typical room over an unheated basement

mb_il

Given the variation in the potential heat loss, if it ends up being verified at a higher number beyond what the radiant panels themselves could generate, is it technically possible to feed a baseboard radiator via a pex loop built into the radiant track?

One thing I’m concerned about is flow rate; I’ll have about 700-750 feet of pex loop for the radiant panels themselves, plus another 100ish feet to feed the baseboard radiators, all being fed by a 3/4 copper pipe coming up through the garage via a 5 loop manifold.

hot_rod

hopefully your pex loops are 300’ or less in length?

The panel rad would be on a loop if its own, not included in the radiant loop

mb_il

hot_rod, yes planning on 3 loops for the radiant running 200-250 feet in length. Could I run the runtals in parallel, with 1 runtal on 2 of the 3 loops, or should I plan a dedicated loop for each (5 loops total)?

hot_rod

Maybe a seperate zone for the Runtal, a two stage thermostat to control the system.