Radiant and forced hot air garage set up questions, need advice.

[JOE.G]

Hi, My garage is 28x28x10 first floor and second floor is 28x28x8.
Right now I have on the first floor a Big Max 80 K hanging unit ( I know it is over sized ). The second floor has a ventless propane fireplace which I only turn on if I am going to be in the man cave. There are stairs with a door at the top which I do leave open most of the time. I have ceiling fans on both floors.

The first floor has 4 250 foot loops of radiant in the floor and I have yet to hook it up. What type of unit should I go with for the radiant? I have a propane manifold in place already and I would like a simple venting system with a unit that takes up little space preferably hanging on the wall.
I have had good luck with Navien products.

I keep the heat on 45-50 Deg all winter unless I am out there then I turn it up. Everything is insulated including the ceiling of the first and second floor.

I was thinking I would hook up the radiant and leave that at 45 to 50 then use the Big Maxx for the quick rise if needed. At this time it does feel chilly even at 70 because the concrete is cold.

Any tips, does this make sense? I may not even use the Big Maxx once radiant is hooked up. Thank you

 

[Dana]

The very smallest NHB-55 would have sufficient capacity to handle the likely combined load of both the garage & first floor, assuming there is glass in the windows and insulation in the walls, as reported. But the minimum-firing rate of the NHB-80 is the same as the -55, so it won't be any more prone to short cycling, if you're not quite sure what the load is or if you want a slightly faster recovery from temperature setbacks. HTP's UFT-080W might be cheaper, and is easier to install in most systems, especially if you're also installing an indirect water heater zone. With the UFT's low pumping head fire tube heat exchanger it doesn't need to be plumbed primary/secondary the way the NHBs do.

I'd personally be inclined to install a cold climate 3/4 ton Fujitsu mini-split -9RLS3H for both heating and cooling in the upstairs space, and just continue to use the Big Max for the lower half. The Fujitsus have a "Minimum Heat" mode which keeps it at 50F, and the efficiency is pretty amazing- substantially cheaper heat than condensing propane in most markets (even high electricity price markets.) In heating mode that 3/4 ton Fujitsu can deliver 15,000 BTU/hr @ +5F, (11,000 BTU/hr even at -15F). Unless there is a lot of window area upstairs that should be plenty.

For yuks, run a LoadCalc or CoolCalc load calculation for the upstairs space, using aggressive assumptions about air tightness & R-values, etc.

 

[Sponsor]

 

[JOE.G]

I'll run the Calcs as soon as I get a second. The Room upstairs has a door to the out side and 4 windows, the down stairs has a man door, garage door ( highest R Value door I could buy ) and 3 windows, all windows are new Energy windows. The walls are all a full actual 2x6 with the correct insulation.

I am not worried about cooling the building as it never gets uncomfortable in the summer in its location, I am really only concerned with heating the floor on the 1st level, Maybe down the road adding a base board upstairs but it is not in the current plans. Upstairs is just a Man cave that is finished but not a full time living area and the current fireplace has it up to temp in a very short time.

 

[Dana]

Propane, or NG?

Got a ZIP code?

NY is a pretty big state covering three climate zones- Saranac Lake is a lot cooler than NYC or the Hamptons, and might actually use some fuel to maintain 50F over the winter, whereas in the Hamptons it'll probably just coast at 50 or better just on solar gains except during cold snaps, assuming its reasonably air tight with low-E windows.

 

[Jadnashua]

A slab on grade without insulation and a vapor barrier beneath it could tend to suck a lot of the heat you add out. Getting the slab a bit warmer will go a long ways towards the comfort level, though.

 

[JOE.G]

I am in the Catskills Mountains of NY, I have Insulation and a vapor barrier under the slab, I have 4 foot cement walls which are probably 3/4 under ground on the three sides. We use LP here.

 

[Dana]

I am in the Catskills Mountains of NY, I have Insulation and a vapor barrier under the slab, I have 4 foot cement walls which are probably 3/4 under ground on the three sides. We use LP here.

Residential retail LP is running ~$2/gallon in NY statewide. Residential electricity runs about 18 cents/kwh.

The source fuel energy content of LP is 91,600 BTU/gallon. Burned at 95% efficiency in a condensing boiler that delivers (0.95 x 91,600=) 87,020 BTU/gallon into the heating system water. So to deliver a million BTU (MMBTU) it takes (1,000,000/87,020=) 11.5 gallons, which at $2/gallon is $23/MMBTU.

Heating at ~80% efficiency with the Big Max would cost $23 x (95%/80%)= $27.31/MMBTU.

The Fujitsu 9RLS3H tests at a rated HSPF of 14BTU per watt-hour, or 14,000 BTU/kwh. So it takes (1,000,000/14,000=) 71.4 kwh/MMBTU, so at 18 cents/kwh that comes to ($0.18 x 71.4= ) $12.85/MMBTU.

So at those price points heating with a better-class mini-split costs just a bit more than half what it costs for condensing propane, less than half the cost of heating with the Big Max.

Maybe you can get propane for a buck a gallon, but most people can't. I doubt electricity in the Catskills is running north of 30 cents/kwh, which is what it would take to cost as much as heating with propane.

Are the concrete foundation walls insulated (at least on the above-grade part)? An 8" concrete wall fully above grade has U-factor of about 0.75 BTU/hr per square foot per degree F temperature difference, which adds up to a HUGE heat loss if it's 3' tall around 3/4 of the perimeter (assuming the 4th side is mostly insulated garage door). That's 3' x (3 x 28') = ~250 square feet. Even lower elevation towns like Oneonta have average mid winter temps in the low 20s, higher up you're looking at 20F or even cooler for the December-February hourly mean temp. With an indoor temp of 50F that becomes an average difference of 30F, so just the uninsulated 3' of above grade foundation is going to be losing about:

U0.75 x 250 ' x 30F= 5625 BTU/hr...

...x ~2000 hours = 11.25 MMBTU for just the 3 months of winter, just for the above grade foundation wall losses at an indoor temp of 50F.

Insulating it to R10 with 2" of foil-faced polyiso strapped to the wall with 1x 4 furring through-screwed to the wall with masonry screws, with half-inch gypsum (necessary to meet fire code) would cut the U-factor to about 0.093 BTU/hr per square foot per degree-F, which (do the math) burns through only 1.4 MMBTU for the 3 months of winter.

Another, potentially better solution is insulating on the exterior, digging down to the footing (or 2' below grade) with 2.5-3" of EPS would be worth it. (It would have to be done with EPS rather than polyiso, which can soak up ground water over time). There would need to be some Z-flashing at the transition from framed wall to foundation to properly direct bulk water to the exterior, and the exterior can be protected with any number of purpose made finishes.

 

[JOE.G]

When I poured the slab I did put 2.5 EPS around the outside of the walls, The only wall that does not have it is the front wall which is 2 ft high and 6 foot wide on each side of the door.
The Fujitsu 9RLS3H Seems like a nice set up, But I would still have cold floors, I can feel the cold halfway up in my shop standing there unless I run the big maxx for a while and I did install ceiling fans to bring the heat down but the cold is coming off of the concrete.

Dana Thank you for the ideas, The Mini split I think I would have Done if I did not have the Big Maxx yet, I am not sure the cost to switch would make sense at this point. If I have an issue in the future I would replace it then.

I do have heat loss from around the garage as I can see especially in the front that the snow and frost melt away about 6 in to a ft from the building.

 

[Dana]

Almost any cold-climate 3/4 mini-split (or even the half-ton Mitsubishi FH06NAH) would probably do nicely for your upstairs space.

If there is already a huge amount of heat leaking through the slab edge & footing, the last thing you want to do is use the slab as the heating radiator for maintaining the standby 50F room temps without doing something to better manage that heat loss. If the Big Max is used for maintain room temperature, an electric boiler running off a floor thermostat could be turned on a few hours in advance of when you intend to use the space. That's more expensive to run than the propane burner if it were being used for primary heat, but it's not a huge expense if it's only being used intermittently to bring the slab up to 60F or for a few hours or days. Electric boilers are dirt cheap, pretty rugged, and easy to install.

If the space around the building isn't paved, digging down a foot and installing 2.5-3" thick EPS "wing" insulation 2' wide (or even 4' wide) around the perimeter will be at least as good as insulating the footing:

It's often useful to slope the wing insulation to improve drainage, which keeps the footing drier, and thus better protect it from frost heaving in a less-heated building:

 

[Fitter30]

1/2" pex is 30 - 35 btu's per foot, 30k btu's. Design flow .9 gpm, water temp 5-10* over thermostat setting. Can run water a little hotter but would want a thermostat with f!oor sensor. Could use a water heater for a boiler and with a condensing boiler need a drain for condensate.

 

[JOE.G]

I have a Drain to use, I have a few different to choose from How hot do you usually want the water for a system like this? Mini Split Would have been nice when I first did this build I am not sure now if it would be or not.

 

[Jadnashua]

If the garage area might ever freeze, you should consider filling the boiler with a suitable antifreeze mix. Note, that will decrease the heat transfer ability and make things a bit less efficient, but will keep the system from freeze damage and potential leaks.

Something like Ditra-Heat-Duo would likely have a bit faster response, but would only work if you wanted to tile the garage area. https://www.schluter.com/schluter-us/en_US/Floor-Warming/Schluter®-DITRA-HEAT-DUO/p/DITRA_HEAT-DUO

If you're lucky and have cheap electric, either an electric boiler or electric floor warming may work for you. The Ditra-Heat-Duo has a thicker fleece on the bottom to provide a bit of thermal break with the substrate versus other versions.

 

[JOE.G]

I think i would keep it water, If I was ever to shut off heat totally off Id drain it down. I was thinking of putting race deck down.