Heating a large garage .... need real world advice please

[xtal_01]

OK ... so I am just putting the roof on my new workshop ... need to think about heating next.

The shop is just over 4000 sq ft.

I have built it completely by myself ... even put the roof trusses up myself ... not too bad for an old guy (I am 61 now)

I am a machinist by trade but as I tell everyone I work on everything from "tractors to toys".

The attic is 1000 ..... don't need heat there ... though I will insulate it so heat from the lower bay can bleed in and "maybe" keep it from freezing.

The lower level has and office/washroom area ... about 400 sq ft ... might need a separate heater for this area.

The main part is three bays ... about 21 x 52 with 16 to 18 ft ceilings.

I used 2 x 6 construction ... so I will have R19 or R21 in the walls.

The roof trusses have and energy heel so I have 24" even above my wall edge ... I will put 12 - 18 inches of insulation and still have a 6" air gap under the roof.

I put 2" of foam under the slab ... plus insulated the edges 24" down and 24" out with 2" of foam

I live in Vermont ... don't have to worry about cooling (only 5 days on average above 90 ... but we can hit -30).

I am thinking I will build my own swing doors .... they are 14 x14 ... and put 2" of foam in them.

I look at a lot of heating systems .... I think I have it down to two ... but don't have any real world knowledge with a building this big or either heating system.

Things like radiant or tube heaters won't work. When I put an RV in the bays, I don't have the clearance needed.

To not spend a fortune heating, I plan to keep all bays just above freezing (say 40 or 45 deg) and then heat only the bay I am working in that day to say 65 or 70

I can't use a furnace (standard or condensing) as they have a minimum turn down temp of 55 or 60 deg (checked with two factories .... need relatively warm return air or they will corrode).

So in the end, I think it comes down to a Modine style hanging heater or a boiler system with air handlers.

The hot water boiler looks interesting but seems very complicated. Always having to heat water ... zoning valves ... pumps .... lots of pieces and parts. The one nice thing air handlers are relatively cheap so you can put one at each end of a 50 ft bay and get decent heat distribution.

The Modine style heaters are simple. Hang them up ... pipe them in ... turn them on.

I think I would want one with a sealed combustion chamber (using outside air). Not that my shop is so dusty but if I am sanding a car ... or doing some woodworking ... or some painting ... or ... Just would be safer to have outside air for the combustion chamber.

This unfortunately eliminates the cheaper heaters like MrHeater ... only about $650 each.

Modine makes an HDS series ... about $2000 each

I called Modine .... no problem with turn down temps and such .... recommended a 75K BTU unit or 100K BTU unit to be safe.

I did the heat load calculations myself .... 72K BTU ... amazed me how close they were!

Now, here is my problem with the Modine units ... the 75K unit has a heat throw of 38 ft .... the 100K unit has a heat throw of 42 ft

On a 52 ft shop ... will I be cold down the far end?

The factor could not give me an answer ... things like "it should work" ... and "it might be colder down the far end" ... I hate things like "should" and "might" when I am looking at spending about $8K when all is said and done on heating three bays.

I was going to mount these against the back wall .... and that is want they recommended also ... but will I freeze standing by the main doors?

I can go with a ceiling fan for some added mixing.

I have just never seen one of these heaters to know how well they will work.

Any suggestions or advice would be great.

Thanks ... Mike

Here a link to my facebook page with some videos of me building: https://www.facebook.com/michael.csele/

 

[thammel]

There will be enough natural convection that you shouldn't be concerned about how far the heater will "throw" the heat. The most important thing to do will be to insulate very well and seal all gaps. I'm a fan of Reznor heaters and like their UDAS sealed combustion one. That's what I have.

 

[kbeefy]

Thats an awesome building!

I'm no HVAC guy but I have a hanging heater in my 2400' poorly insulated shop.
In my opinion, the only time the 'heat throw' is pertinant is when the heater is actually blowing air. Everything will equalize when the heater cycles off. Where you place your thermostat will affect thigs, you might find it too hot at the heater end while it's running if your standing over there.

Sounds like you'll be pretty well insulated. A couple ceiling fans should help even things out.

 

[thammel]

And great FB site!! Wow!! I just scanned but lots of neat videos! What projects are planned for inside the new shop? By the way, glad to see another church singer - I'm also one!

 

[xtal_01]

Thanks guys! I have built a few much smaller workshops but for some reason the toys keep getting bigger. I am in rural VT ... well ok, all VT is rural, our largest city is only 42,000

I seem to be working on all kinds of farm equipment lately. Lots of small farms ... old equipment that dealers don't want to deal with. I am a city boy and didn't know the difference in a round or square bailer ... or what the heck a tedder was. Many of these guys are barely hanging on. I try to keep them going ... never charge them.

My wife (I met her 15 years ago) broke her neck diving into a pool when she was 12. She needs care ever 4 hours so she had never traveled. I was living in SC (a widower) when I net her (I was originally from Canada ... near Niagara Falls) .. got the idea of getting an old RV and making it accessible ... this way I could do her care while traveling. Got a 10 year old unit ... $18K. When to have a lift put in it ... they wanted $25K! So I cut a new door and built my own lift. I gutted the interior .... put in hospital beds .. and built a lift that goes from front to back. Worked great ... even lived in it while we built the house (not so much fun at -30) but we saved $1000 per month in rent.

The RV is now 25 years old and is dead (rusted out floors ...leaking roof ... furnace is dead ... brakes are dead .... roof leaks ... dead).

Time to find another used RV and make it accessible.

I built an elevator for our house ... $40K for a new unit .... I bought a forklift for $1000 ... used the mast ... put together some hydraulics ... about $2K in the project.

I have a lathe, mill and welder ... both are in storage waiting form me to build this shop.

One bay will be for a machine shop.

One bay for storage of the RV (they last a lot longer when not out in the weather).

One bay for everything else ... working on a car ... wood working ... what ever I am doing that day.

Plus I have way toooooo much junk ... hit and miss engines ... my blacksmithing stuff ... all kinds of junk.

I also build electrical panels for a few companies ... not many but a few a year .... I take any work I can do out of the house so I can be at home to care for my wife.

Anyway .... that is the story.

I could only afford to build the shop if I did it myself ... taking me forever but it is slowly taking shape.

Thanks again for the advice !

 

[Firstram]

Anything worth having is worth working hard for, very nice!

 

[xtal_01]

There will be enough natural convection that you shouldn't be concerned about how far the heater will "throw" the heat. The most important thing to do will be to insulate very well and seal all gaps. I'm a fan of Reznor heaters and like their UDAS sealed combustion one. That's what I have.

Looks like that model has been discontinued. They have many more. I will give a call and see what they suggest. Thanks!

 

[xtal_01]

Thats an awesome building!

I'm no HVAC guy but I have a hanging heater in my 2400' poorly insulated shop.
In my opinion, the only time the 'heat throw' is pertinant is when the heater is actually blowing air. Everything will equalize when the heater cycles off. Where you place your thermostat will affect thigs, you might find it too hot at the heater end while it's running if your standing over there.

Sounds like you'll be pretty well insulated. A couple ceiling fans should help even things out.

Awesome! I am an insulation fan ... I sealed up our house tight and in the coldest winter month, I am at about $200 with natural gas. I am planning on sealing the shop as well as I can. Thanks!

 

[xtal_01]

And great FB site!! Wow!! I just scanned but lots of neat videos! What projects are planned for inside the new shop? By the way, glad to see another church singer - I'm also one!

The wife loves to sing ... I can't carry a tune.

She has sung as a soloist for about 30 years ... weddings ...funerals ...

She was asked to form and direct a community chorus about 15 years ago ... did that for 10 years.

She then formed a new group and directs that: https://www.vermontsfreedomandunitychorus.org/

 

[xtal_01]

Anything worth having is worth working hard for, very nice!

A little hard work never killed anyone. Even my wife, being paralyzed from the shoulders down has a full time job .. she has worked since she graduated from college ... first as part time, then when we go married I got her to get her drivers license and she then went full time. I give her credit ... not many people would live in an old RV in VT for three winters so they can build a house ... but we did it!

 

[fitter30]

Need one heater to offset the garage doors load especially when a door is open.

 

[PoorUB]

One answer would be to put two 45K BTU heaters at opposite ends.

Another answer, a couple ceiling fans to stir up the air.

 

[xtal_01]

One answer would be to put two 45K BTU heaters at opposite ends.

Another answer, a couple ceiling fans to stir up the air.

There is not much cost difference between 45 and 100 K units. This would almost double the cost.

I do think ceiling fans would greatly ehelp.

Thanks!

 

[Ak Jim]

The wife loves to sing ... I can't carry a tune.

She has sung as a soloist for about 30 years ... weddings ...funerals ...

She was asked to form and direct a community chorus about 15 years ago ... did that for 10 years.

She then formed a new group and directs that: https://www.vermontsfreedomandunitychorus.org/

Looks like a great group, they sound really great!

 

[Bert_]

I can't quite picture your layout. Is each bay separated by walls?

A single unit heater is going to have very uneven temperatures without airflow between the bays.

 

[xtal_01]

I can't quite picture your layout. Is each bay separated by walls?

A single unit heater is going to have very uneven temperatures without airflow between the bays.

Yes, I have a wall between each bay. The building was roughly 64 wide x 52 long. I divided it into three bays (two with 14 x 14 doors ... one with access only from the inside and and off ice in the front part).

I was planning on one heater per bay. This way I can control the temperature of each bay.

I would leave all of the bays just above freezing most of the time.

I would turn up the heater in the bay I would be working in that day.

I originally put some (ok lots) of videos on YouTube showing the build

If you go to that link ... at about 6 min in, you can see an interior wall and it kind of shows the three bays.

Thanks ... Mike

 

[Bert_]

Yes, I have a wall between each bay. The building was roughly 64 wide x 52 long. I divided it into three bays (two with 14 x 14 doors ... one with access only from the inside and and off ice in the front part).

I was planning on one heater per bay. This way I can control the temperature of each bay.

I would leave all of the bays just above freezing most of the time.

I would turn up the heater in the bay I would be working in that day.

I originally put some (ok lots) of videos on YouTube showing the build

If you go to that link ... at about 6 min in, you can see an interior wall and it kind of shows the three bays.

Thanks ... Mike

Ok.

75,000 for those small bays is a LOT of heat. I would be guessing more like 45,000, but that's nothing more than a guess.

For reference I heat 40x100x16 with a single 100,000 tube heater. That's in Iowa and we don't see -30 but maybe -20 at the coldest.

 

[xtal_01]

Ok.

75,000 for those small bays is a LOT of heat. I would be guessing more like 45,000, but that's nothing more than a guess.

For reference I heat 40x100x16 with a single 100,000 tube heater. That's in Iowa and we don't see -30 but maybe -20 at the coldest.

I do agree ... 75K seemed very high. My furnace in the house heats on low so 60K for the entire house.

The factory did recommend 75K ... and I used an online load calculator .... it said 72K .... maybe they are being way more conservative?

Mike

 

[Bert_]

I do agree ... 75K seemed very high. My furnace in the house heats on low so 60K for the entire house.

The factory did recommend 75K ... and I used an online load calculator .... it said 72K .... maybe they are being way more conservative?

Mike

What did you use for a load calculator?

 

[xtal_01]

What did you use for a load calculator?

HVAC Load Calculation - Maunualj - Whole House Loadcalc

ManualJ load calculator, HVAC calculation, Whole house, - www.loadcalc.net

www.loadcalc.net

Maybe I was wrong but then why would the factory come up with the same answer?

I can post all the number later ... or maybe run them on a different calculator.

 

[Bert_]

Factory is shooting from the hip. Could be fairly accurate based on experience but they have to be conservative.

I have used that calculator before with good results.

Are you calculating each space individually as if it had 4 outside walls? Or as a group since the interior walls won't have meaningful heat loss?

 

[Bert_]

I would rather leave the building at 50* all winter and maybe turn it up to 55 or 60* at the most if you plan to be out there all day.

I think you end up more comfortable than with a 70* air temp but cold floor and cold tools. Doesn't change the cost much.

You will have to decide what works best for you.

 

[WisJim]

I'm not going to recommend anything in regard to heating equipment, but I want to remind you that a good job of sealing up the building and then insulating thoroughly and properly (no poorly cut batts, etc) will make a BIG difference in heating cost and in comfort. I'd recommend Tyvek or similar under your siding to help seal against drafts and infiltration, and a good job of spray foam in odd spaces where your batts won't fit well. I'm assuming from what you said above that you plan on fiberglass or mineral wool in the walls, but I would recommend spray foam if it is in the budget. And insulate the walls between the bays so when you do raise the temp in one bay you aren't wasting heat on the adjoining bay.

 

[xtal_01]

Factory is shooting from the hip. Could be fairly accurate based on experience but they have to be conservative.

I have used that calculator before with good results.

Are you calculating each space individually as if it had 4 outside walls? Or as a group since the interior walls won't have meaningful heat loss?

I did calculate (I was in a hurry) the walls as outside walls ... but I didn't think just one of the 4 walls would throw off the calculations that much. I will re-run them and see what I get.

Just didn't have the time .... $25K in roofing (standing seam) all came in dented and scratched. They are making me go through it piece by piece and document the damage. Fun times!

 

[xtal_01]

I'm not going to recommend anything in regard to heating equipment, but I want to remind you that a good job of sealing up the building and then insulating thoroughly and properly (no poorly cut batts, etc) will make a BIG difference in heating cost and in comfort. I'd recommend Tyvek or similar under your siding to help seal against drafts and infiltration, and a good job of spray foam in odd spaces where your batts won't fit well. I'm assuming from what you said above that you plan on fiberglass or mineral wool in the walls, but I would recommend spray foam if it is in the budget. And insulate the walls between the bays so when you do raise the temp in one bay you aren't wasting heat on the adjoining bay.

Spray foam is out of the budget .... I used it on the house in spaces like the floor joists hitting the rim board.

My house is large ... only two bedrooms but we hit ledge when digging to rather than spend $30K to dynamite a basement we went up ... basement is the ground floor ... entire house is second floor.

That gave me 4800 sq ft above ground.

I sealed and insulated everything tight. I even caulked ever sheet of drywall it. I crawled along the floor then sealed the sill ... even after using a sill seal.

In the coldest winter month, I pay about $250 per month .... that is very good for our area.

I am using the same construction for the shop. 2 x 5 walls ... lots of caulking ... a 24" rise designed into my trusses where they hit the wall so I can have 12 - 18" of insulation right to the edge and still have a 6" air gap under the roof.

Mike

 

[u3b3rg33k]

OK ... so I am just putting the roof on my new workshop ... need to think about heating next.

The shop is just over 4000 sq ft.

I have built it completely by myself ... even put the roof trusses up myself ... not too bad for an old guy (I am 61 now)

I am a machinist by trade but as I tell everyone I work on everything from "tractors to toys".

The attic is 1000 ..... don't need heat there ... though I will insulate it so heat from the lower bay can bleed in and "maybe" keep it from freezing.

The lower level has and office/washroom area ... about 400 sq ft ... might need a separate heater for this area.

The main part is three bays ... about 21 x 52 with 16 to 18 ft ceilings.

I used 2 x 6 construction ... so I will have R19 or R21 in the walls.

The roof trusses have and energy heel so I have 24" even above my wall edge ... I will put 12 - 18 inches of insulation and still have a 6" air gap under the roof.

I put 2" of foam under the slab ... plus insulated the edges 24" down and 24" out with 2" of foam

I live in Vermont ... don't have to worry about cooling (only 5 days on average above 90 ... but we can hit -30).

I am thinking I will build my own swing doors .... they are 14 x14 ... and put 2" of foam in them.

I look at a lot of heating systems .... I think I have it down to two ... but don't have any real world knowledge with a building this big or either heating system.

Things like radiant or tube heaters won't work. When I put an RV in the bays, I don't have the clearance needed.

To not spend a fortune heating, I plan to keep all bays just above freezing (say 40 or 45 deg) and then heat only the bay I am working in that day to say 65 or 70

I can't use a furnace (standard or condensing) as they have a minimum turn down temp of 55 or 60 deg (checked with two factories .... need relatively warm return air or they will corrode).

So in the end, I think it comes down to a Modine style hanging heater or a boiler system with air handlers.

The hot water boiler looks interesting but seems very complicated. Always having to heat water ... zoning valves ... pumps .... lots of pieces and parts. The one nice thing air handlers are relatively cheap so you can put one at each end of a 50 ft bay and get decent heat distribution.

The Modine style heaters are simple. Hang them up ... pipe them in ... turn them on.

I think I would want one with a sealed combustion chamber (using outside air). Not that my shop is so dusty but if I am sanding a car ... or doing some woodworking ... or some painting ... or ... Just would be safer to have outside air for the combustion chamber.

This unfortunately eliminates the cheaper heaters like MrHeater ... only about $650 each.

Modine makes an HDS series ... about $2000 each

I called Modine .... no problem with turn down temps and such .... recommended a 75K BTU unit or 100K BTU unit to be safe.

I did the heat load calculations myself .... 72K BTU ... amazed me how close they were!

you can absolutely can do a condensing system.

I just did a Rinnai i120CN (95.5% condensing combi boiler) + low temp air handler.

the rinnai is 100% stainless internals, and a grundfos pump.
4 row HX low temp capable ECM air handler, also with a grundfos pump. sweat/propress.

the boiler will modulate from 15k to 120kBTU for heating. with outdoor reset off, it'll just make 140F water, and adjust the fire to keep the outlet temp, no matter the return temp.

outdoor reset is FANTASTIC for bringing down the discharge temps in warmer weather so you don't get that "i'm dying while the heat is on" feeling. you can set your own curves to match your heat load.

if you want multiple zones, you can either do a zoned air handler, or buy a prefab pump panel from menards/blueridge, etc. they will sell you a complete kit, ready to fill.

baseboards are great for garages if you have the space. they're right where the cold air is.

or you can do multiple fan coils (one per bay). boiler don't care.

here's what I used:

https://www.supplyhouse.com/Rinnai-I120CN-i120CN-120000-BTU-Condensing-Wall-Mounted-Combi-Boiler-NG

https://e4m6s3b8.rocketcdn.me/wp-content/uploads/produits/VenTum/ventum-flyer-EN.pdf

 

[mrbill55]

Have you thought about gas fired infrared heating units?

I used Soleronics for my old 10,000sq/ft bodyshop in the northeast and saved a ton of money (ROI was less than 3 years vs the old gas fired, forced air units) as I was not heating the air, but select surface areas.

Bill S.

 

[Firstram]

Have you thought about gas fired infrared heating units?

I used Soleronics for my old 10,000sq/ft bodyshop in the northeast and saved a ton of money (ROI was less than 3 years vs the old gas fired, forced air units) as I was not heating the air, but select surface areas.

Bill S.

Not too good over the RV but would sure be the ticket in the other two bays!

 

[mrbill55]

Not too good over the RV but would sure be the ticket in the other two bays!

I had them mounted on the sides of the bays they were needed in, that way they heated the floor area where I was going to be, on long enough, the concrete becomes a thermal mass in those areas as well, radiating heat out a bit further. Difference in costs vs a forced air system (IE: 11 high mounted units) was paid for in the first three full years....For the other 6 years, they saved me enough money to pay a good portion of my mortgage off.

Bill S.

 

[xtal_01]

you can absolutely can do a condensing system.

I just did a Rinnai i120CN (95.5% condensing combi boiler) + low temp air handler.

the rinnai is 100% stainless internals, and a grundfos pump.
4 row HX low temp capable ECM air handler, also with a grundfos pump. sweat/propress.

the boiler will modulate from 15k to 120kBTU for heating. with outdoor reset off, it'll just make 140F water, and adjust the fire to keep the outlet temp, no matter the return temp.

outdoor reset is FANTASTIC for bringing down the discharge temps in warmer weather so you don't get that "i'm dying while the heat is on" feeling. you can set your own curves to match your heat load.

if you want multiple zones, you can either do a zoned air handler, or buy a prefab pump panel from menards/blueridge, etc. they will sell you a complete kit, ready to fill.

baseboards are great for garages if you have the space. they're right where the cold air is.

or you can do multiple fan coils (one per bay). boiler don't care.

here's what I used:

https://www.supplyhouse.com/Rinnai-I120CN-i120CN-120000-BTU-Condensing-Wall-Mounted-Combi-Boiler-NG

https://e4m6s3b8.rocketcdn.me/wp-content/uploads/produits/VenTum/ventum-flyer-EN.pdf

Interesting! I have only seen older systems with one (or two) pumps near the boiler. I see this one has a pump at the handler .... that is how they use the tankless heater.

What I like about this system is you can put two handlers per bay so the heat is evenly spread.

 

[xtal_01]

I had them mounted on the sides of the bays they were needed in, that way they heated the floor area where I was going to be, on long enough, the concrete becomes a thermal mass in those areas as well, radiating heat out a bit further. Difference in costs vs a forced air system (IE: 11 high mounted units) was paid for in the first three full years....For the other 6 years, they saved me enough money to pay a good portion of my mortgage off.

Bill S.

I will have to do a bit more homework. I looked at two of these units. Even on a wall they wanted almost 8 ft of clearance ... just don't have that much room ... but I will check into it again.

 

[xtal_01]

you can absolutely can do a condensing system.

I just did a Rinnai i120CN (95.5% condensing combi boiler) + low temp air handler.

the rinnai is 100% stainless internals, and a grundfos pump.
4 row HX low temp capable ECM air handler, also with a grundfos pump. sweat/propress.

the boiler will modulate from 15k to 120kBTU for heating. with outdoor reset off, it'll just make 140F water, and adjust the fire to keep the outlet temp, no matter the return temp.

outdoor reset is FANTASTIC for bringing down the discharge temps in warmer weather so you don't get that "i'm dying while the heat is on" feeling. you can set your own curves to match your heat load.

if you want multiple zones, you can either do a zoned air handler, or buy a prefab pump panel from menards/blueridge, etc. they will sell you a complete kit, ready to fill.

baseboards are great for garages if you have the space. they're right where the cold air is.

or you can do multiple fan coils (one per bay). boiler don't care.

here's what I used:

https://www.supplyhouse.com/Rinnai-I120CN-i120CN-120000-BTU-Condensing-Wall-Mounted-Combi-Boiler-NG

https://e4m6s3b8.rocketcdn.me/wp-content/uploads/produits/VenTum/ventum-flyer-EN.pdf

So it looks like the boiler is about $3K ... and each of handlers about $2K (times six) ?

Can I guess that even if the building calculates out to 75K BTU per bay, I only need say 100 or 120 K boiler as you are only heating one zone at a time?

Thanks

 

[u3b3rg33k]

Interesting! I have only seen older systems with one (or two) pumps near the boiler. I see this one has a pump at the handler .... that is how they use the tankless heater.

What I like about this system is you can put two handlers per bay so the heat is evenly spread.

there's two sizes, the larger unit would probably be more suitable for you. I would recommend that and ducting/zoning it for better distribution. the handler/FCU is rated for .75" WC, and mine has no issues with a merv13 media filter on it.

So it looks like the boiler is about $3K ... and each of handlers about $2K (times six) ?

Can I guess that even if the building calculates out to 75K BTU per bay, I only need say 100 or 120 K boiler as you are only heating one zone at a time?

Thanks

this particular boiler is a combi boiler, it does heat and hot water via an internal heat exchanger. so it's two appliances in one. the heat only version is slightly more than half the price. I wanted the space efficiency and cost savings of the single appliance, venting, plumbing, etc.



it's built for 2 stage (you can set your own fan speeds to a resolution of 10 CFM), and mind you those numbers are at 70F return air.
140F supply water and 40F return air will be a LOT more BTU and basically the same discharge air temp.

the tankless boiler will produce setpoint heating water (in my case 140F for simultaneous DHW+CH), and the fire will modulate based on CH temp setpoint. so the colder the water that is returned to the boiler, the more it'll fire to hold 140F supply temps.
that's different from a fixed fire furnace where you get a delta T based on return air and constant fuel input.

I designed for 140F to guarantee staying in condensing operating mode, and to be able to use PVC venting. My envelope only needs 48kBTU peak output, ever, so I have plenty of capacity to spare.

 

[xtal_01]

there's two sizes, the larger unit would probably be more suitable for you. I would recommend that and ducting/zoning it for better distribution. the handler/FCU is rated for .75" WC, and mine has no issues with a merv13 media filter on it.

this particular boiler is a combi boiler, it does heat and hot water via an internal heat exchanger. so it's two appliances in one. the heat only version is slightly more than half the price. I wanted the space efficiency and cost savings of the single appliance, venting, plumbing, etc.



it's built for 2 stage (you can set your own fan speeds to a resolution of 10 CFM), and mind you those numbers are at 70F return air.
140F supply water and 40F return air will be a LOT more BTU and basically the same discharge air temp.

the tankless boiler will produce setpoint heating water (in my case 140F for simultaneous DHW+CH), and the fire will modulate based on CH temp setpoint. so the colder the water that is returned to the boiler, the more it'll fire to hold 140F supply temps.
that's different from a fixed fire furnace where you get a delta T based on return air and constant fuel input.

I designed for 140F to guarantee staying in condensing operating mode, and to be able to use PVC venting. My envelope only needs 48kBTU peak output, ever, so I have plenty of capacity to spare.

I have a tankless water heater here now ... love it. I would want to go the same way. I have a rough in for a shower ... nice to leave the mess in the shop. Using PVC and pex is cheap .... so 140 is a good idea.

Definitely something to think about!

Thanks for all the advice !!!!!!!!!!!!!!

 

[Bert_]

I will have to do a bit more homework. I looked at two of these units. Even on a wall they wanted almost 8 ft of clearance ... just don't have that much room ... but I will check into it again.

8' is strange. I would double check that requirement.

I just hung a couple 80k radiant tube heaters in a shop and they required 42" clearance to combustibles below the heater.


I love tube heaters and would choose one over forced air if it's possible

 

[xtal_01]

8' is strange. I would double check that requirement.

I just hung a couple 80k radiant tube heaters in a shop and they required 42" clearance to combustibles below the heater.


I love tube heaters and would choose one over forced air if it's possible

I will definitely double check. Maybe different manufactures have different requirements. I know one was 81" (just remember because it such an odd number) and the other 96"

Maybe some are less ... I will check ... Thanks!

 

[PoorUB]

I called Modine .... no problem with turn down temps and such .... recommended a 75K BTU unit or 100K BTU unit to be safe.

I did the heat load calculations myself .... 72K BTU ... amazed me how close they were!

Now, here is my problem with the Modine units ... the 75K unit has a heat throw of 38 ft .... the 100K unit has a heat throw of 42 ft

On a 52 ft shop ... will I be cold down the far end?

I got thinking about this, then in another post you mention 75K BTU per bay.

Is you load for the whole shop 75K B\TU? Or two bays at 75K BTU?

When we install floor heat we run on 25-30 BTU per foot,
4,000 sqft x 25 BTU is 100K BTU.
4,000 sqft x 30 BTU = 120K BTU.
If you are 75K BTU total I wonder if you are a bit short, but then I look at you construction and you are making certain the building is tight so perhaps 75K BTU total is good.

Just looking for clarification.

 

[xtal_01]

I got thinking about this, then in another post you mention 75K BTU per bay.

Is you load for the whole shop 75K B\TU? Or two bays at 75K BTU?

When we install floor heat we run on 25-30 BTU per foot,
4,000 sqft x 25 BTU is 100K BTU.
4,000 sqft x 30 BTU = 120K BTU.
If you are 75K BTU total I wonder if you are a bit short, but then I look at you construction and you are making certain the building is tight so perhaps 75K BTU total is good.

Just looking for clarification.

Using the online calculator, it came up with 75K BTU per bay ... that is per 1100 sq ft at 18 ft high. The way it was explained to me, it is like having double the sq footage because the ceiling is over double the height of a normal house.

This would mean my 3000 sq ft building is more like a 6000 sq ft house ... well at least when considering the walls (still only one ceiling).

So the total of all three bays is 225K BTU

Mike

 

[PoorUB]

Using the online calculator, it came up with 75K BTU per bay ... that is per 1100 sq ft at 18 ft high. The way it was explained to me, it is like having double the sq footage because the ceiling is over double the height of a normal house.

This would mean my 3000 sq ft building is more like a 6000 sq ft house ... well at least when considering the walls (still only one ceiling).

So the total of all three bays is 225K BTU

Mike

Wow! I did HVAC in North Dakota fort 20 years. 30 BTU per square foot will heat a building with 20 foot side walls. With you concerns with having a tight building you could easily heat is on half of what they are saying.

Like I said, 4,000 sqft x 30 BTU = 120K BTU. If you want to go with the 1100 sqft per bay, x 3 bays = 99K BTU. The three 45K heaters will end up with 108 after efficiency loss. I might go with 60K units, but honestly, if it were my place it would be three 45K heaters. Your biggest problem is ceiling height, you need a ceiling fan to stir it up.

We did a 34,000 sqft truck shop, 30 BTU per sqft. Heats it just fine, we could have went smaller. common steel building, nothing special. Probably leaked like a sieve and it seemed like and overhead door was opening every half hour getting trucks in and out.

I heat an 1950's, poorly insulated, 900+ sqft rambler on 24K BTU input down to -30F, then I enable second stage heat.

 

[TurnipTruck]

I heat a 40x60 with an upstairs, and 80kbtu keeps it at 55*F without running constantly, even during a week of -25.
I am near the ocean so my wintertime temperatures are somewhat moderated, but we still have seven months of winter.

75kbtu per bay? Nay!