heater size question.....again...michigan here

[ED26]

heater size question.....again...Reznor 30 vs 45k UDAP

27x24x9 attached garage. R13 walls, R43 in ceiling. Insulated Garage Door, two man doors, one window over work bench.

Looked all over online and searched the website for recommendations. I get not oversizing the heater.

Probably maintain current temp through winter 50/55...then crank up to 65 before going out to tinker...

Its not a workshop (not in it everyday), usually have one car in a bay and other open to do projects.

Will the 30k do the job, that is what the local contractor is recommending.

it gets windy by us; just dont want the 30k if it takes forever to get to 64 degrees...if you know what im saying

 

[PennWoodworks]

Is this a one car garage you are intending to heat with a 30k btu heater???

I have a 2.5 car garage that’s heated by 17k btu electric heater. My walls are less insulated as well. Takes about an hour to get the garage up to 63 F from 55F. I put in a WiFi thermostat though so I just do it from my phone before I go in.


Sent from my iPhone using Tapatalk

 

[ED26]

Correct, two car 24x27x9 attached garage.

Will have one car in a bay the other bay is usually open for working area.

I’m looking at a Reznor UDAP 30K or UDAP 45K natural gas unit heater.

30k unit is 25k output btu
45k unit is 37k output btu

 

[bdbecker]

You missed a "2" in your first post, it makes much more sense now. Yes, 30k BTU is probably what you want. Maybe 45k depending on how cold you get - what type of temps to you see in your area?

 

[Trapps]

Both Reznors you mention are great units. The price difference (excluding install) is pretty negligible in the big picture. I'd go with the UDAP-45. My theory (who knows how bad this advice is given my current level of insanity) is that the larger unit will work less and be more efficient and therefore last longer than the UDAP-30. Both units have the same 'footprint'. It will also insure you can overcome Michigan winters which can be quite cold.

 

[bdbecker]

Both Reznors you mention are great units. The price difference (excluding install) is pretty negligible in the big picture. I'd go with the UDAP-45. My theory (who knows how bad this advice is given my current level of insanity) is that the larger unit will work less and be more efficient and therefore last longer than the UDAP-30. Both units have the same 'footprint'. It will also insure you can overcome Michigan winters which can be quite cold.

Bigger is not always better when it comes to gas furnaces. Too big, and you risk short cycling the heater, which increases wear and tear and shortens its service life. The OP is probably on the line between the 30k and 45k units, depending on what part of MI he lives in.

 

[Greg5OH]

Metro detroit? 35k,
Copper Harbor? 80k

 

[ED26]

Metro Detroit off the coast tho so we get lots of wind.

A friend of mine said Reznor is made in Mexico now and support blows.

I’m not HVAC expert but I know from research modine and sterling made in USA

Trying to find quietest unit since attached garage

 

[finn]

I had an 18k when I lived in suburban Chicago. It was ok until we got cold snaps of the single digits or lower. Couldn’t really keep up at those temperatures, although it was ok at mid teens and above ambient temperatures. I didn’t heat the garage when I wasn’t using it, though, so there was a lot of mass to bring up to temp.

Either 30 or 40k should be adequate for you, considering you plan on maintaining some heat all of the time.

 

[Greg5OH]

to know for sure...heat loss calculation.
ball park of, i know a guy who did X....go with 45
I too am finishing up a 45 install, ADP unit made in Canada.
Im south of Flint, very little wind as Im in a forest.
980 sq feet 10' ceiling with a 4x24 section being 12 feet.
Should be in a nice happy medium with a 45k 80% eff.
R13 walls, 12" of blow in on the attic, big *** window.

 

[WP9]

Lived on the East side (near Lakeside Mall) and had a 20x20x8.5ft shop attached to garage. 2x6 walls with r19 fiberglas, Anderson windows(4) , double insulated doors to outside, ceiling R32. I had a Reznor closed combustion 45K heater and it worked flawlessly for the 18 years I was there. I could bring the temp up 15 degrees within 10-15 minutes and short cycling was not too bad. I could have used the 30KBTU model just as effectively, but wanted a fast heat up.
For your size, assuming you have garage doors to contend with( which tend to be "leaky", I would think the 45K model would be a good choice. They are noisey, especially when you are working within 8-10 feet of the unit.
I now have a larger shop ( approx9000 sq ft r21 walls r49 ceiling.) and have a mini split. Jury is out as I have only had it running since October. Amazingly quiet, cannot raise temp quickly like a large gas unit, but heating bills are about double those of the gas fired Reznor. ( then again size of shop is much larger)
Looking forward to air conditioning in the summer, it will be a plus.

 

[Showkey]

Beacon Morris which appears to be a division or brand of Sterling is made in the US.

 

[Trapps]

Bigger is not always better when it comes to gas furnaces. Too big, and you risk short cycling the heater, which increases wear and tear and shortens its service life. The OP is probably on the line between the 30k and 45k units, depending on what part of MI he lives in.

Agree 100%.

But between the two options the OP listed, 30 & 45, I'd opt for the 45. If he'd said between 30 and 75, 100 or 150, then I'd have gone with the 30.

 

[yeldogt]

With his level of insulation I can't see needing more than 30k --- make sure no leaking doors.

Smaller heaters make a space more comfortable due to the longer run times --- there will be more comfort when the heater is running. A larger heater will heat the air and stop -- heat the air and stop. You want longer run times.

With a well insulted space and having NG available --most people end up keeping spaces warmer with NG being so cheap.

 

[jvitez]

Get the 30k. As other have said, the two reason's you don't want a heater that's too big for the space:

1. Short cycling. AFAIR it takes ~10-15 min for a fuel burning heater to reach steady state maximum combustion efficiency. Short cycling is therefore less efficient as the heater will not reach the stated efficiency rating. There's also a potential for rusting out the heat exchanger if it can't get hot enough to eliminate condensation. Burning NG and propane create lots of water vapour.

2. Comfort. A short blast of hot air then a long period off creates heat stratification. Heat doesn't rise, hot air rises. Still hot air ends up at the ceiling and you're cold. That's the beauty of modulating gas valves, being able to keep the fan on in proportion to the heat generated, so you always feel warm air and the air is kept circulating minimizing heat stratification.

 

[cadunkle]

Consider what temperature you want to keep it at and temp when in use. I have a 45k Sterling heater in a 24x30x10 deteched in the mid atlantic region with R13 walls and R21 ceiling and it would take about 90 minutes to get from 50* to 72*. I like to be warm, I did my time in the cold and warming my hands on a torpedo heater. 90 mins was too long for my taste even with a wifi thermostat to use ahead of time when I thought of it, granted it was serviceable to get started after 20-30 mins of the heater running.

I now keep the garage at 60*, the heater hardly runs any longer to maintain that temp and I'm out there often enough that it's worthwhile to cut time to warm up in half. A nice bonus is even after it's up to 70*-72* my tools and projects don't feel so cold.

The other consider is the rollup door. You lose a lot of heat in just a minute or two to move a vehicle in or out. Not as big a deal if bringing a hot engine inside as that helps recovery time, but it's still substantial. If I were to do it again I'd have gone larger. probably a 60k Sterling.

As others have said, a smaller heater with longer run times will last longer and be more efficient, as well as be more comfortable. If oversizing for rapid temp rise some companies offer a stainless heat exchanger option with can extend life of the unit. For your case with great ceiling insulation and attached I'd be inclined to go with a 45k-50k heater, particularly if you only want to maintain 50* when not in use which is typically the minimum recommended by manufacturers for good heat exchanger life.

 

[toyotadriver]

Since you plan to maintain the temp all the time and just raise it when you work out there, I’d go with the 30k. If you left it off all the time and only turned it on when you work out there, then I’d go with the 45k

 

[Tizzy]

I just put a 75k separated combustion in a 32x40x12. R-19 walls, R-38 ceiling. R-13 overhead doors. I wish I’d have went with the 90.
My opinion, and I’m no hvac guru, get the 45.

 

[ED26]

im close to where you used to live (east side)...spoke w the HVAC guy again, he said the 30k will heat better. my plan is to keep it probably 50-55 all the time. then crank to 65 an hour or so before going to work out in garage.

some of the online specs between 30/45 online i found; curious if any of these stick out between the two and what would make better sense

30k efficiency - 82
45k efficiency - 83

30k kw/h - 8.8
45k kwh - 13.2

30k BTU out put - 24600
45k BTU out put - 37350

30k Power Watts - 109
45k Power Watts - 155

30k discharge temp rise - 50
45k discharge temp rise - 55

30k air volume cfm - 456
45k air volume cfm - 629

30k output velocity fpm - 475
45k output velocity fpm - 656

30k fan output hp - .02
45k fan output hp - .03

30k fan motor rpm - 1550
45k fan motor rpm - 1550

30k fan diameter - 10
45k fan diameter - 10

 

[BobotheMonkey]

A lot of this depends on design. I did the same thing and was hoping for some kind of a blanket answer. I use a 20K BTU electric heater to heat my 24x40x10 garage in western WI. Its perfectly capable above 0 and doesn't take more than an hour or so to heat up from 40. My garage has r-19 walls and R43 ceiling, but has 1 inch of foam board on the ceiling and all the walls and ceiling were seam sealed with spray foam. Assuming its a relatively tight structure, the 30 should be just fine. If you want it to be able to hold 65 the few days a year it doesn't go above zero, would think the extra head room on the 45k is the ticket. I think the 30 would still do the job, but it would run quite a bit below zero. If I ever have an issue with the 20k heater, I have a small propane back up, but haven't seen any long below 0 stretches yet. If it were me, 30k is what I would choose, but I wouldn't expect it to maintain 65 if its 20 below...

 

[ED26]

A lot of this depends on design. I did the same thing and was hoping for some kind of a blanket answer. I use a 20K BTU electric heater to heat my 24x40x10 garage in western WI. Its perfectly capable above 0 and doesn't take more than an hour or so to heat up from 40. My garage has r-19 walls and R43 ceiling, but has 1 inch of foam board on the ceiling and all the walls and ceiling were seam sealed with spray foam. Assuming its a relatively tight structure, the 30 should be just fine. If you want it to be able to hold 65 the few days a year it doesn't go above zero, would think the extra head room on the 45k is the ticket. I think the 30 would still do the job, but it would run quite a bit below zero. If I ever have an issue with the 20k heater, I have a small propane back up, but haven't seen any long below 0 stretches yet. If it were me, 30k is what I would choose, but I wouldn't expect it to maintain 65 if its 20 below...

i am in process of insulating now; R43 total in ceiling, and the walls are r13. vinyl siding. new garage door insulated, two man doors, and one larger window over back work bench. one wall adjoins living space; so three exterior joining walls.

HVAC guys says the 30 will heat better; although it is not a shop. man, im torn. the wife will be putting her car in at night and leave in morning. i do not have any paint projects, just regular garage tools and a space to tinker so ideal it doesnt make much sense to keep it heated 55 all winter long here in michigan although nat gas is cheap.

 

[BobotheMonkey]

I guess I'm not sure it was asked, but what type of insulation? Assuming fiberglass or blown cellulose. Both have wind washing issues. Is the attic area ventilated where the wind will do this, or totally enclosed? Are you covering with drywall or unfinished OSB? Especially since you have one wall attached, I would think you're completely fine with 30k. They say approximately 70% of heat loss is from air leakage, so make sure your seals are up to snuff and spray from any penetrations.

Super rough calculation says about 18k for your needs. This calculation would be 4 exposed sides and being able to heat to 65 even when extremely cold. There are so many factors that it is always hard to say for sure without inputting every piece of data into a load calculation. My guess is you are overthinking it. Like I said, I am happy with my 20k heater and have nearly 4000 cubic feet more than you do on a stand alone building, but I don't expect it to keep up well below zero either. I seam sealed everything and put up foam board as a thermal break before finishing the ceiling. Total R-value is 43(not total wall value), but I do have wind washing, so take the R38 of fiberglass that sit on top of the foam with a grain of salt. Its a vaulted ceiling though, so blown in wasn't a great option due to settling. I think you'll be happy with a 30k. I'd trust the HVAC guys.

 

[bdbecker]

Based on the NG prices here, it costs about $0.14 to run a 30k heater for an hour. Unless you have some serious leaks, I doubt your heater will run that hard keeping your garage a 55F once it stabilizes after a car leaves/enters. My guess is you'll see your gas bill go up by $30, maybe $40.

 

[cadunkle]

Wow that's cheap. I did the math the other day and it costs about $.59/hr to ruin my 45k heater. $.14/hr works out to about $.47/therm vs $1.42/therm on my last bill in the mid atlantic. At $.47/therm in would cost $.21/hr to run a 45k heater.

 

[ED26]

I guess I'm not sure it was asked, but what type of insulation? Assuming fiberglass or blown cellulose. Both have wind washing issues. Is the attic area ventilated where the wind will do this, or totally enclosed? Are you covering with drywall or unfinished OSB? Especially since you have one wall attached, I would think you're completely fine with 30k. They say approximately 70% of heat loss is from air leakage, so make sure your seals are up to snuff and spray from any penetrations.

Super rough calculation says about 18k for your needs. This calculation would be 4 exposed sides and being able to heat to 65 even when extremely cold. There are so many factors that it is always hard to say for sure without inputting every piece of data into a load calculation. My guess is you are overthinking it. Like I said, I am happy with my 20k heater and have nearly 4000 cubic feet more than you do on a stand alone building, but I don't expect it to keep up well below zero either. I seam sealed everything and put up foam board as a thermal break before finishing the ceiling. Total R-value is 43(not total wall value), but I do have wind washing, so take the R38 of fiberglass that sit on top of the foam with a grain of salt. Its a vaulted ceiling though, so blown in wasn't a great option due to settling. I think you'll be happy with a 30k. I'd trust the HVAC guys.

Fiberglass. R13 faced parallel in bottom cord, r30 perpendicular unfaced over to the r13. Attic is ventilated. Soffit vent to the ridge vent. I put the vent Shute in ea cavity and will use the r13 & pieces of r30 to place tight under the Shute over the top plate. If that makes sense.

We get some gusty winds in our location ...house has 3/4 foam board over osb sheathing and then newer vinyl siding. Fiberglass man doors newer and insulated 16x7 garage door.

Unsure on the ceiling. Probably a wood 5/8 product. Don’t want to tape and mud etc.

 

[BobotheMonkey]

If the vent baffles go all the way to the peak, you should be good. You are going to lose heat through convection either way. The more I learned about insulation, the more I found that fiberglass kind of *****. Foam board and spray foam are the best options, but you have to work with what you have! I think you'll be happy with the 30k. Worst case, you can can sell the smaller heater and buy the bigger one or put foam board over the bottom of the ceiling. I chose the foam board route due to having an attic area over part of the shop where I could only get r19 in the cavity.

 

[ED26]

I’ll possible do the foam on ceiling before install my finish product to add to insulation value.

 

[bdbecker]

Wow that's cheap. I did the math the other day and it costs about $.59/hr to ruin my 45k heater. $.14/hr works out to about $.47/therm vs $1.42/therm on my last bill in the mid atlantic. At $.47/therm in would cost $.21/hr to run a 45k heater.

You are right... that is too low. I must have dropped the "1" off the price I have loaded into my excel sheet. I had "4.96" instead of what was probably meant to be "14.96" as the price per therm. Updated to the current average price of $15.76/therm, I now get $0.46/hour to run a 30k heater.

Thank you for spotting that!