Unit Heater Placement and Size

[dsl_mech]

Can someone assist in deciding how many BTU unit heater I need and where would be the best place to install it?

I have a 32' x 40' shop. 11' wall height with 13' in peak due to scissor trusses. Will have R-20 insulation in walls and minimum R-28 in ceiling. Might go to R-40 in ceiling. Have two 10' x 10' R-16 overhead doors and one man door. No windows. Its a working shop and will probably heat no higher then 55F while working. Drop it down slightly while unused. Climate is Vancouver, BC, Canada just above border of Washington state on West coast. Thanks for any suggestions.

 

[American Locomotive]

Do you want a heater that will keep the space warm and provide good comfort, or do you plan to keep the space unheated and want a heater that will crank out a ton of heat and get the space up to temperature in 10 minutes?

 

[dsl_mech]

Do you want a heater that will keep the space warm and provide good comfort, or do you plan to keep the space unheated and want a heater that will crank out a ton of heat and get the space up to temperature in 10 minutes?

Thinking more keep the space warm and provide good comfort. Planning to keep the shop around 55 when working. Hoping to drop down slightly when not in use for extended periods of time to save on some gas (how far not sure right now). I do have plumbing in the building so heat will never be completely off during the heating season. I will have a wifi thermostat and try to turn the heat up in advance when I know im going out there. The odd time I forget I have no problem suffering until it gets to temp. I do not expect the heater to crank out a ton of heat and warm the place up in 10 minutes. Pretty much im hoping to end up with a properly sized heater that works well for the space. Not undersized or oversized. Ive tried to have a few HVAC guys run heat calcs and recommend a size based on the building and so far nobody is interested in doing the actual calculation and seem to be just throwing out a random number.

 

[PoorUB]

What are the HVAC guys telling you for size?

I have a number in my head.

My opinion is most guys aim big. The customer doesn't complain when the heater heats up the space, but put in one too small and we have problems, so they go big.

 

[dsl_mech]

First guy who came out quoted a Lennox LF24-120. Which from my research is from the commercial line of heaters as the LF24 residential garage unit heaters appear to max out at 75,000 BTU. The 120,000 he quoted has an output of 96,000 BTU if I remember correctly.

The second guy who came out and actually asked more questions about my intended use of the shop and required heat level said I would probably be okay with a 30,000 or 45,000 BTU heater.

From my lengthy reading of this forum and google. Im leaning towards a 45,000 or 60,000 Reznor unit.

 

[PoorUB]

I would go with a 60,000 BTU unit heater.

In my opinion the 45,000 is a bit small, but might do it. a 60,000 would be good.

A 120,000 BTU unit heater??

 

[corey5521]

I have a 30x40 shop in TN. 12 foot white metal ceiling with R-30 on top, R20 on the walls with no covering yet. I run an 80K BTU Mr. Heater. Obviously a different climate and the heater is probably overkill but even on the coldest days my shop doesn’t drop below 35-40 degrees and will heat to 65 in 10-15 minutes no problem. I only run the heater while in there but have future plans of a mini split and may try to keep it at 50-55 all winter. The Mr. Heater is great. It’s quiet and efficient. I run two ceiling fans to move the heat down.

 

[corey5521]

Forgot to add that I run it dead center on the back wall. It faces my two 10x12 garage doors.

 

[fitter30]

Size of equipment has everything to do with the insulation and air infiltration. Nobody can size a heater without knowing these things.

 

[klassenl]

On the prairies where I have lived all my life we would start at a minimum of 45000 btu. My shop is a little smaller and lower ceiling. I have no problem keeping it at 10 celcius during the winter with 45000.

Seeing that the coast is more temperate than the prairies that may be enough.

I would likely choose 60000 btu for a little more headroom when it gets cold for long stretches or when you would like it warmer than usual.

 

[dsl_mech]

Thanks for all the suggestions so far. Local supplier with Reznor heaters has every size readily available except for the 60,000. I am waiting to hear back from them how long it would take to get one. I understand the 45,000 may be a little too small. What would be the negative of stepping up to the 75,000 that they have available?

 

[American Locomotive]

Basically a common complaint with oversized unit heaters (or forced hot air systems in general), is that the space doesn't feel "warm" or doesn't feel like it "stays warm" or it "feels like there's a chill".

Basically air can only conduct heat to a surface (metal, concrete, wood, whatever ) so fast. With an oversized heater, it heats the air in the room up very fast. You get a huge rush of hot air, that quickly makes the room feel too warm. The thermostat satisfies, but everything in the room is still cold. The air in the room quickly cools, and then the heater is running again. This will repeat for a while until everything in the room is warm.

A smaller heater will more gradually warm the space up, and it will feel more comfortable. In general, a heating system should be designed so that on the coldest night of the year, the heater is just about running continuously to maintain your set temperature.

 

[PoorUB]

Thanks for all the suggestions so far. Local supplier with Reznor heaters has every size readily available except for the 60,000. I am waiting to hear back from them how long it would take to get one. I understand the 45,000 may be a little too small. What would be the negative of stepping up to the 75,000 that they have available?

I too large unit runs short cycles and does not warm up the heat exchanger well and can rot out from moisture sooner. It will also heat the space up faster and probably over shoot the temp and you may have slight temperature swings. A smaller unit will run longer cycles and the room temp will be more constant. Also the smaller unit will me slightly more efficient, easier on your bank account, but hard to say if it is enough to really notice.

If you can not get the 60K, go with the 75K, but unless you are ready to install the heater I would wait.