Needed: High Efficiency NG HVAC for a 2,100 sf single story building

I've been asked by the owner of a theatrical company about heat for her building.  It is a single story, 36' x 57' building (almost 2,100 sf) with only a little bathroom partitioned off in one corner.  She is presently heating it with a wood stove but wants to run a NG line in and buy a furnace or two.  She wants to house film editing equipment and needs even heat but wants to get away from the wood stove work.  One estimate she got was for two wall heaters, one at each end of the building (there are already ceiling fans to move air in the summer time during live productions) over $5,000 for 94,000 BTUs.(nNo word on an efficiency ratingfor this one)  Another estimate she got was for a furnace and overhead ductwork (building has 9' ceilings) for well over $6,000.  The climate is Northern PA.

The inside of the walls are bare 2 x 4's which have been sprayed with 2 part foam maybe 4" thick and painted.  There are maybe 6 or 8 double hung windows (double pane) maybe 2' wide x 3' high.  The ceiling is made of insulated garage door panels and there are 2 overhead doors in one end.  I guess that makes it sound like it was a multi-car garage at one time!

This job is a tight budget job and I'm looking for some options and/or input for her since I'm a small contractor and an energy auditor and not someone who came from an HVAC background.

In our initial conversation I began steering her toward a sidewall vented unit.  I haven't run a Blower Door yet.  And it's been a while since I was at the building and then it wasn't to do an audit.


Is it feasible to do something without ductwork?

We are in a more rural area. I have yet to find a HVAC co. who does Manual J calc's.  Do I need one?  and ---I've wondered this for a while, Can I learn to do one?

Thanks in advance!

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Keri, my thoughts are that you do NOT want a wall heater at each end, unless uneven heating isn't a concern.  What about cooling?  Is it needed/wanted?  If you go with a high efficiency furnace it will be direct vent.  I would first look at the ceiling/roof air sealing & insulation, & get it "right", to avoid a system that's bigger than necessary, then get energy calcs done somehow.  There are some folks who will do the Manual J, D, S for a couple/few hundred.  Otherwise it's almost a guarantee the system will be oversized.  I would want a ducted system if it were my building; something simple to get the air distributed well.  You can learn the modeling process of course; you'll have an investment in the software (1100-1200?), and a learning curve.  If there is nobody around to do energy calcs maybe you can be that person.

She Does want something even -- that was a stated priority.

I didn't ask about cooling -- I'll do that on the next conversation.

The roof is gabled and metal.  She wasn't sure about insulation but I'll def. look at that when I go.

I already talked to her about over-sizing and how it occurs.

Ductwork wouldn't be as complicated w/o partitions.

I'm going to work on finding someone to do calc's -- i don't mind learning that but can't justify the expense unless I'm doing it regularly.

Thanks for your input.  Kari

One furnace should be plenty, 2 is overkill. You will need some type of ductwork for even heat distribution, it doesn't have to be complicated.

Do you have photos of the building?

Is it a Single room + Bathroom?

Is cooling required? Even a small AC would be an improvement to just using fans.

Will setbacks be used, if so how much/expected recovery time?

OK -- a second vote for one system plus ductwork.

I don't have photos of the building -- but I'll post some when I get them -- I described it from memory.

It is a single room basically.  She has a few temporary partitions for dressing rooms which she is going to remove.  The bathroom is maybe 7' square in the front corner and is heated with a little electric baseboard unit.  Concrete floor throughout.

I have to ask about AC requirements.

I understand T-stat setbacks BUT what is "expected recovery time"? and how is that calc'd?

Thanks -- Kari

If setbacks are employed, how long does the customer expect to take for recovery?

I'd consider putting the furnace in the corner and running an 50' exposed duct the length of the building. Have registers blow across the ceiling to the other side.

You'll have to explain your first question...I'm not an HVAC  specialist so the "time for recovery" needs a definition -- thanks

Recovery time is how long it takes for the building to warm up when coming back for setback. If a customer normally keeps the building at 70 and turns it down to 50 when they aren't there, how long does it take to get back to 70 once the customer turns the heat back up.. If a customer expects a quick recovery time then a larger system is needed.

OK got it...simple enough.  I think with sensitive electronics in the building -- I'm not seeing a 20 deg. set back even when someone isn't there but I will include that info. when I talk to her next.  Thanks -- 

She is OK with one high efficiency unit and some duct work inside the envelope. She started asking about noise from the blower.  I told her it shouldn't be too loud but that if it was a small enclosure with sound-proofing could be built if it was a sealed comb. unit. 

Cooling is one 22,000 BTU "window" unit installed in the wall.  She says with that one unit and a couple of fans it is easy to maintain cooling.

For heating she's looking at a set temp. of 68 deg. with a set back of no less than 60 deg. -- so that would be 8 degrees of change.  If the unit would have to be bigger for shorter recovery, she said she would probably just leave it at 65-68.

A small central AC is most likely to be quieter and more comfortable that a window unit. Using the smallest furnace that will do the job will go a long way to reducing noise complaints. Has she considered going with a heat pump or minisplits? The cost to install the gas line plus the meter fees may cost more than running a heat pump.

At the beginning of the conversation she said she wanted to get a gas line installed.

In these parts if you install central heating or a gas fired WH sometimes you can get the gas line run from main into the building for free.

She hasn't talked about a heat pump or mini splits and seems satisfied with how the AC is working.  Can you ballpark the difference in price for a 90+ gas furnace vs. heatpump or mini splits for me (2,100 sf building)?  This is a tight budget job.  (Also, I haven't checked the electric service yet)

Mini-split will save cost of the ductwork and provide cooling at the same time. Quiet and efficient. Not sure it would be able to handle the entire heating load in your area.

80% furnace is another low cost option if venting allows, and ductwork costs can be kept in check. A 90% is about $500 more, but some of that may be offset by lower venting costs. A 90% will require a drain for the condensate it produces.

Smaller furnaces will be MUCH quieter, don't oversize. Unless the building is leaky a 3 burner (60-75k) should be good for temps down to 10f or so. Doing a proper load calculation is the best bet to determine correct size.


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