How much attic insulation is enough?

[VetteNut]

I planning on getting a Modine hot dawg 30k or 45k installed before winter hits the Chicago area. And am concerned I don't have enough insulation , I don't want to waste all my new heat!

I have an attached 2.5 car (550 sq-ft with 10-ft ceiling) garage. It's currently drywalled and insulated with R13 wall and R30 attic. Also have an insulated garage door. There is only 1 common wall shared with the house, and no living space above it, vinyl siding exterior.

I'm wondering if I should put some blown-in insulation in the attic to get it to R38 or R49? Or am I past the point of diminishing returns?

Also while I'm at it, I've read mixed reviews on the 30k vs 45k for my sized space. The HVAC guy thinks 45k is too big and is worried about cycling. With the minimal price difference, Will I regret going with the 30k unit?

 

[TurnipTruck]

I vote for a 30k, just so it won't short cycle. I would run with your existing insulation this winter as a trial. If it seems as if the heater runs for too long or the gas bill is excessive, add insulation.

 

[CNGsaves]

Any windows ??

That amount of insulation for Chicago is bit skimpy, but you could give it a "trial run" for one winter as above poster says. x2 on going with 30K Btu for 2 car garage, unless you plan on using heater as more "Immediate" heat rather than maintaining a consistent heat.

The 45K heater would be better . . IF . . you rarely turn it on, but when you do, you want garage to be 70 degrees on a winter day in Chicago !!!

Along with more insulation, your game plan should also include improving how airtight the space is, so check all door seals (add weatherstripping), foam electrical outlet wire holes, etc. Good luck.

 

[Radix2]

Try the slantfin app to see the difference in btus with more insulation. It will be really small after R30, especially so considering a garage with the giant door. I agree with CNG more to be gained with keeping out drafts, etc.

 

[VetteNut]

No windows. My garage door normally only opens twice a week during the winter on garbage days. (And when the snowblower needs to come out). I'll look into better weather stripping and such thanks!

I should also say, my intention is to keep the garage at constant temperature. I may turn it up to 70ish to work out there only 1-2 days a month. So having to "heat up fast" is not a priority. So it sounds like to save $30 and skip the 45k unit

I hadn't thought of trying out the R30 for a winter to see how it does, before just adding more to it. It just seemed like not enough.

 

[NUTTSGT]

If you want more insulation, you can buy 40' rolls of R11 (15"OC) for about $10/roll. Just roll them perpendicular to the other batts to blanket the attic. It should give you plenty with the current R30 that you already have.

At $10/roll, it doesn't hurt the wallet picking a roll up here and there. When you get enough for the job, then it's time to get dirty.

 

[Showkey]

I vote for R38 as the minimum and R49 would be the preferred. Blown in cellulose from Menards would likely be the cheapest per sq. ft. While your up there touch up the whole house. Depending on the age of the house IL sorta known for being "light" on insulation standards. ( codes)
Do not cover or block the soffit vents. Attic vents in this area ?
Insulate the trap door.

Weather stripping on the garage doors would be a good first start.

 

[VetteNut]

Great idea I hadn't thought of putting more rolls down! My garage attic and house attic are separate. My house attic actually has R38 in it, That might actually be cheaper than blow-in. As I'd have to hire for the blown-in for health issues, I was quoted at around $1200 for both attics. (Bringing garage to R49 and house to R60). House was built in 2008, we paid for the upgraded insulation then (to R30/R38) but the codes have gotten stricter in the last few years as R49 is now the current code.