Another Heater Sizing question

[eyes11]

I had a 24'x30'x8 detached garage. R18 walls/R40 ceiling. I was using a 45k btu Reznor natural gas heater. I maintained the heat at 45F all winter long and would heat it up to 65-70F 2-3 times per week. I now added on 24'x32'x10' to the same detached garage basically doubling the square footage.

First question is what size ceiling natural gas heater should I get.

I have a 60k btu Reznor natural gas heater in my attached garage that is probably over sized a bit so....

Second question: Would flip flopping the two heater be my best option? 60k btu in the detached 1470 sqft garage and put the 45k btu in the attached garage (approx 26x32)?

Last question: If i would decide to go with a traditional house furnace for my detached garage (1470sqft) what btu should i look for. I was thinking that if i go the traditional furnace route i would look for a two stage. The furnace should maintain the 45F all week long with the low stage and I would have the second stage of the furnace to pick up to 65-70F. I like the furnace option just not sure what btu 2 stage to look for.

Thanks in advance.

Additional info. Central Wisconsin. Detached garage is all R18 walls/R40 ceiling. Natural gas ran to detached garage already.

 

[Jackfre]

The least cost would be to simply add another wall furnace. Going with a central system will be costly, take up space and not give you much gain. I would suggest that you add a Rinnai EX38

 

[Showkey]

You might want to check the different furnace instructions.

Many warn that room intake temperature should be above 50-55* under normal operation
. The issue is prolong low temp intake causes heat exchanger corrosion. They specifically warn that 40-45* intake air is too cold.

I would suspect a conventional furnace would be more susceptible to corrosion. A high efficiency furnace operating at 60*-65* would likely use far less fuel than the 80% ceiling mount units at 45*. You would have to deal with the condensate.

I have 1000 sqft well insulated detached witha 45k btu. It had a 60k prior that rusted out. I keep it 60* and estimate the NG cost is less than $1 a day in the coldest months. ( We are in the same area .)

 

[D45]

I used to have a 45k heater......it ran alot and also took alot time to bring the temp up to a comfortable working environment

I initially thought about adding a second, smaller heater and just tap into the 3/4" line by adding a T fitting

Then I thought, just sell the 45K and buy a larger heater.............which I did

I ended up getting another Hot Dawg, just in the 75,000 BTU version (HD 75AS-0111)

Some comparison specs for the 45K vs the 75K

45K FAN SIZE: 10"
75K FAN SIZE: 14"

45K INPUT: 45,000
45K OUTPUT: 36,000

75K INPUT: 75,000
75K OUTPUT: 60,000

45K HEAT THROW: 27 feet
75K HEAT THROW: 38 feet

45K AMP DRAW: 3.7
75K AMP DRAW: 2.5

The added BTUs and the longer heat throw was perfect. The 45k heater did not have a larger enough or powerful enough fan, to blow and push the heat down the 60 length of my garage

I sold my 45K for $400 and bought a new 75K for $575 shipped......a good price I think, plus I got the initial 45K heater for free

 

[eyes11]

How do ppl like a traditional furnace for garage heat. I'm leaning towards a 80kbtu 2 stage furnace thinking that the low stage will be ok for maintaining even 50F and 2nd stage for pick up. Just nervous the 60k btu Reznor might be undersized for 1470 sqft.

 

[Showkey]

How do ppl like a traditional furnace for garage heat. I'm leaning towards a 80kbtu 2 stage furnace thinking that the low stage will be ok for maintaining even 50F and 2nd stage for pick up. Just nervous the 60k btu Reznor might be undersized for 1470 sqft.

Traditional furnace 80-96% work fine but they must be mounted off the floor to meet codes when used in a garage. 90% plus solve a few issues PVC venting and outside air combustion. Condensate must be dealt with and high eff furnace are not suppose to ever freeze unless completely drained of the water.

Two stage is going to run the cost up and provide no fuel saving. Two stage is all about comfort in a home heating......low gentle heat, quiet, low draft. None of the benefits apply to garage heating. Two stage is overkill and over bill. Plus it adds complexity to simple job.

Ceiling mount heater is hard to beat for out of the way convenience uses no floor space. Meets code for garage space.

Bottom line, your building is well insulated and sealed 30-80k will do the job.
40-50-65k will be just fine........don’t over think this.

If you really work the numbers 80k furnaces are used to heat a well insulated 4000/5000 sqft 3 bedroom 3 bath home.

 

[Bad00SS]

How do ppl like a traditional furnace for garage heat. I'm leaning towards a 80kbtu 2 stage furnace thinking that the low stage will be ok for maintaining even 50F and 2nd stage for pick up. Just nervous the 60k btu Reznor might be undersized for 1470 sqft.

I have one in my attached garage. its about 30x26. I made a stand to get it up off the floor for code. It heats up fast. zero complaints. My detached building i'm looking at the 50k btu mr heater big maxx ceiling hangar for the 32x28.

 

[Jim greengo]

How will the addition be connected to existing garage?
Will it be walled off with a door dividing things,or 1 big wide open area?

 

[eyes11]

It will be one big space