Reznor unit heater size?

[etbjr]

Looking to put a Reznor UDAP in my 36x72x12 building, 2x6 construction on the walls. R15 spray foam on the walls and ceiling R38-40 blown fiberglass. Was first thinking a 125K heater, then changed my mind to a 150k. The place where I’m getting the heater from is out of stock on the 150k, but will sell me a 175k for the same price, do you guys think I’ll be oversized with the 175k? Location KY. Thanks!!

 

[Dagny]

I bet they are all too big. Have the guy you are buying it from do a heat loss calculation on your building. Pretty sure Reznor don't sell to big boxes.

 

[etbjr]

I’ve had several heat calculations done, ranging from 75k-. Have called Reznor directly and one rep said 100 would be plenty another one said 200k...so I’ve gotten three local cals done by HVAC companies and they all say 150k. I’m not getting the unit from a box store, it’s a local store that’s sells Reznor.

 

[nadogail]

Can the 175K heater be modified to limit it to 150K, maybe by plugging some gas jets?

 

[etbjr]

Really don’t want to do something like that, even if it is doable.

 

[Snip]

etbjr, I'm a bit south of you in Crossville Tn. Maybe a little more milder winter temps? I built a similar sq ft building 40x66 with 14 ft walls. When I started asking questions about heating it using a Reznor radiant heater using R19 FG in the walls and around a 30 blown into the sealing most of my answers were in the 100k range. The shell is up but I have not finished the interior or heated it yet so I cannot tell you if it is correct yet but I feel confident from the feedback i got the 100k unit will do what i need. A couple of ceiling fans will help. While in the planing stages a couple of years back I ran across a smoking C//L deal on 2 100k units and 60' of tube and reflectors and wasn't sure if I would need one or both. The current plan is to use one with about 50' of tube and save the other unit as a spare

 

[purediesel]

My heated shop area is 49x47x16 which is just over 200 sq ft smaller than yours and I installed a UDAS 115k unit (88k output) and it heats the area great. I am in the process of finishing the wall insulation with 1.5" XPS foamboard so its not even sealed that well. The ceiling is around a R44 or so with blown in fiberglass. I also have 2 man doors and 1 24' insulated overhead door on the west wall that needs new seals to make things worse.

 

[etbjr]

I’m pretty sure that the 125k(120) which is 99,600 output would work, just a little undecided if it’ll be a little bit small is why I’m considering the 150k. The heat throw on the 150k is 69ft vs the 125k at 60ft is another reason also with my shop at 72ft long, although I do have 4 60” ceiling fans installed which will help distribute the heat a lot.

 

[C2F]

https://www.loadcalc.net/

Use this site for your calculation. It allows you to select for your area. With the building design with the insulation. Post what it says

 

[etbjr]

Well, if I entered it all in correctly, it said 42,396. Seems quiet low to me compared to other online calculators I’ve used, I don’t know.

 

[C2F]

Well, if I entered it all in correctly, it said 42,396. Seems quiet low to me compared to other online calculators I’ve used, I don’t know.

That is quite low. How many sq feet is your house and btu furnace? And what’s the coldest it gets around you? My area Can see 5F

 

[Dagny]

I'M in the business almost everyone installs too big.

 

[C2F]

See if they sell a 2 stage heater

 

[etbjr]

I'M in the business almost everyone installs too big.

Would you mind recommending a size?

 

[Showkey]

Would you mind recommending a size?

2500 sqft 42k is way too small.

The simple manufacturers chart will get you very close and make an adjustment for climate and insulation.

125k will do the trick. 75k too small 175k too big.

 

[zmotorsports]

I’m pretty sure that the 125k(120) which is 99,600 output would work, just a little undecided if it’ll be a little bit small is why I’m considering the 150k. The heat throw on the 150k is 69ft vs the 125k at 60ft is another reason also with my shop at 72ft long, although I do have 4 60” ceiling fans installed which will help distribute the heat a lot.

My building is 50x60x16 with the shop portion being 40x50x16 so about the same cubic feet as yours. When my contractor spec'd out the heater for mine he came up with requiring a 100k btu gas-fired heater. I wanted just a little bit more as a cushion because my 20x50x16 RV bay would draw some of the heat away from the shop and IF I needed to open that wall up to heat the RV bay then I had that option as I didn't want to have to winterize our coach any more.

When pricing there was a pretty good jump between a 100k btu Reznor and the 125k but not much more between the 125k and the 150k so I just went right to the UDAP 150. It heats the shop fantastic and now being in the middle of the third winter and have experienced temperatures in the past all the way down to single digits at times I am very pleased I went a bit more than the 100k but I think the 125k would also have been adequate. The other main contributor is how well I had the shop insulated. Even in teens outside and the shop up to temperature the heater only kicks on a couple times per hour and our gas bill is less than our last place with a third of the square footage detached shop.

 

[etbjr]

My building is 50x60x16 with the shop portion being 40x50x16 so about the same cubic feet as yours. When my contractor spec'd out the heater for mine he came up with requiring a 100k btu gas-fired heater. I wanted just a little bit more as a cushion because my 20x50x16 RV bay would draw some of the heat away from the shop and IF I needed to open that wall up to heat the RV bay then I had that option as I didn't want to have to winterize our coach any more.

When pricing there was a pretty good jump between a 100k btu Reznor and the 125k but not much more between the 125k and the 150k so I just went right to the UDAP 150. It heats the shop fantastic and now being in the middle of the third winter and have experienced temperatures in the past all the way down to single digits at times I am very pleased I went a bit more than the 100k but I think the 125k would also have been adequate. The other main contributor is how well I had the shop insulated. Even in teens outside and the shop up to temperature the heater only kicks on a couple times per hour and our gas bill is less than our last place with a third of the square footage detached shop.

I’m glad you saw this, your post about your heater and shop size is the main one I’ve been comparing to. You’re right, yours is just a little larger than mine on cubic feet with your 16ft ceilings. I figured it at 32,000 and mine at 31,104. I agree with others, I think the 125k will work, but I like the fact that the 150k has a heat throw of 69ft vs the 60ft of the 125k. With mine being 72ft long I think that’ll help, but I do have the four 60” ceiling fans in there, I just need to make my mind up and gets some heat!

 

[etbjr]

Zmotorsports, did you sized yours to the 50x60x16 or the 50x40x16? If I’m reading this right you wanted that cushion for the RV bay, so more than likely sized it included that space if you needed to heat it.

 

[zmotorsports]

Zmotorsports, did you sized yours to the 50x60x16 or the 50x40x16? If I’m reading this right you wanted that cushion for the RV bay, so more than likely sized it included that space if you needed to heat it.

We originally sized it for just the shop and it came out under the 100k requirement which is why the contractor bid in a 100k heater. I had to convince him to go a little larger knowing the large heat sink the concrete would be for the RV bay pulling heat from the shop.

When we started pricing them is when we found the pretty large price jump from 100k to 125k but a much smaller price increase from 125k to 150k. I made the decision to go right to the 150k just in case I had to open up the wall or ventilate between the shop and RV bay as I was dead set against having to winterize the coach any more and wanted it ready to travel at any given time, even at the small increase in expense to heat it. Even in single digit temps the furthest corner and coldest section of the RV bay hasn't dropped below about 39-degrees so far. Usually it is around 44-46 degrees in the dead of winter without opening the man door or any extra measures to move heat from the shop to the RV bay.

The throw from the 150k heater is great and even diagonally across my shop it gets quite toasty in the machining area of the shop. I aimed my heater directly towards the lathe and mill and here was my thinking, I thought when machining I am merely standing and not exerting myself so I would be more prone to be chilled vs. anywhere else in the shop where I would actually be working and moving about so I wanted the most heat concentrated to the back machining corner of the shop.

An unplanned scenario that I discovered is that the warm air hits that back corner of the shop and diverts around the other two perimeter walls working up towards the front of the shop near the large overhead doors. This is the perfect scenario because you want the least insulated area to be the last area the heat gets to otherwise you're just pushing the heat right to the least insulated area, which is the overhead doors. It works perfectly and is comfortable anywhere I am at in the shop and the only are I actually feel any air movement is in the machining area when the heater blower motor kicks on. When I turn my ceiling fans on I set them on the lowest setting just to push the heat down but not fast enough to feel any air movement. In the summer months I turn my ceiling fans up to the highest setting and they do help to aid in cooling.

As for the Reznor UDAP in general, I LOVE it. I had an old Reznor 75k in my last shop when I first built it and it worked great and was fairly quiet when the blower motor engaged. About 4 years or so before we sold our last place our A/C unit in the house went on the fritz and we upgraded the home furnace and A/C unit and also included a new heater for the shop knowing it was on its last legs. My friend who I had quote the heater carried Modine line and suggested the 75k Hot Dawg heater for my shop. After installing it I was frustrated with just how loud it was. Sounded like a jet taking off whenever the fan motor came on. When we built the new shop I was adamant on going back to a Reznor and a friend just installed a UDAP 75 in which I was impressed with. My Reznor UDAP150 is fairly quiet and even when filming in the shop the heater can barely be heard when the blower motor comes on, whereas our last place I had to quit filming when the fan engaged.

As an added bonus, the gas consumption was a lot less than our last place as well. Our monthly gas bill between our last home (1200 ft2) and shop (1150 ft2) was nearly $300 at the coldest part of winter and so far our highest gas bill at the new place with the 2500 ft2 main level of the house and 3k ft2 detached shop/RV garage has been $177.00. I contribute much of that savings to both the house and the shop being much better insulated. The house was certified as an energy star home before we purchased it and both the house and the shop are built with 2x6 construction vs. 2x4 at our last place.

Hope that information is helpful.

 

[etbjr]

2500 sqft 42k is way too small.

The simple manufacturers chart will get you very close and make an adjustment for climate and insulation.

125k will do the trick. 75k too small 175k too big.

Thanks for that pic! I’ve been reading alot of your posts also on sizing, what is your shop and heater size again, I can’t remember? Want to do some comparisons, thanks!

 

[Showkey]

2500 sqft 42k is way too small.

The simple manufacturers chart will get you very close and make an adjustment for climate and insulation.

125k will do the trick. 75k too small 175k too big.

Thanks for that pic! I’ve been reading alot of your posts also on sizing, what is your shop and heater size again, I can’t remember? Want to do some comparisons, thanks!

My shop is 1000 sqft with 50k Beacon Morris. Well insulated in cold climate. I replaced a 75k Lennox in the shop because of board failure and ( bad) rust. The Lennox was 18 years old and came with the home purchase so use is not known.

That Lennox was vented horizontal with B vent.......the metal was literally paper thin from corrosion after X years of use.

 

[etbjr]

I do agree the 175 is too big, so my decision is between the 125k or the 150k. The 125k is 99,600 output, so approximately 38 btu sq/ft, 150k is 124,500 output, around 48 btu sq/ft. Really don’t want to be on the small side if and when the 16x10 garage door is opened. I thinking the 150 would help recover faster, but not sure if it’s oversized too much to cause problems??

 

[zmotorsports]

I do agree the 175 is too big, so my decision is between the 125k or the 150k. The 125k is 99,600 output, so approximately 38 btu sq/ft, 150k is 124,500 output, around 48 btu sq/ft. Really don’t want to be on the small side if and when the 16x10 garage door is opened. I thinking the 150 would help recover faster, but not sure if it’s oversized too much to cause problems??

I do like how quickly my 150k recovers from opening an overhead door to pull a car in or out, however, I have no comparison to the 125k. I don't see how it could be a huge difference.

 

[Bert_]

The 2 suggestions for heater size you get on this forum are too big, and way too big.

In my business shop it's got a 100k tube heater. Building is 40x100x16. Honestly the heater could be smaller.

 

[etbjr]

The 2 suggestions for heater size you get on this forum are too big, and way too big.

In my business shop it's got a 100k tube heater. Building is 40x100x16. Honestly the heater could be smaller.

This is what I don’t understand, a couple have said the two heaters are too large for my area, but when I do a search for btu requirements per region of the country etc.. I keep seeing 40-45 btu sq/ft. These two heaters put me 3 btu on the low end and 3 on the high. Now I understand insulation plays a big part, and I am WELL insulated I think, 3”-6” of open cell spray foam in the walls and R38-40 blown in fiberglass in the ceiling, sooo that should let me get away with being on the low end, but not sure how low I could go. The only reference I have is I do run a 22,000 btu kerosene heater now while I’m in there and it brings the temp up 3 degrees an hour, which I think is very good considering the size if the space. The four ceiling fans are definitely doing they’re part. Last started out at 45 inside, two hrs later 54 inside. 100btu is probably doable, but I wouldn’t want any smaller I don’t think with the research I’ve done in Garage Journal.

 

[Bert_]

It's been 0* highs here for several days in a row. Building is 40x100x16 with 6" fiberglass in walls, I think around r38 ceiling, no slab insulation, and 2 12x14 insulated doors.

It's stays as warm as I want it even if you open the doors several times a day. It has 100k tube heater. You have a smaller shed, better insulation and live farther south. You don't need more heat.

Btu/ sqft is not a good number to go by. Usually ends up with a grossly oversized system.

 

[etbjr]

This is real, it's been 0* highs here for several days in a row. Building is 40x100x16 with 6" fiberglass in walls, I think around r38 ceiling, no slab insulation, and 2 12x14 insulated doors.

It's stays as warm as I want it even if you open the doors several times a day. It has 100k tube heater. You have a smaller shed and live farther south. You don't need more heat.

Btu/ sqft is not a good number to go by. Usually ends up with a grossly oversized system.

Probably doesn’t matter for sizing, but you have a tube heater and I’m getting forced air.

 

[Bert_]

Probably doesn’t matter for sizing, but you have a tube heater and I’m getting forced air.

From what I have seen the tube heater has more comfort at lower air temperature. It's like the sun shining on you.

Compared to forced air they should both maintain the same temp.

 

[Bert_]

You're calculation of 42k is probably right. You'd be looking at a 60k because these are 80% heaters. I wouldn't argue if you want a little more 75 maybe 100k but don't think you need more it gets into the category of grossly oversized.

Gets old when all the time people here recommend a heater 3x oversized.

Gotta remember also that you probably only have a week at the outdoor design temp. Even with the minimum heater you have plenty to spare most of the winter.

 

[etbjr]

Well the 125k is on order, more post to come when I get it. Since the distributor didn’t have the 150k in stock (they only had the 125k and 175k) I knew the 175k would’ve been too big so I went with the 125k so I didn’t have to order from somewhere else with the possibility of getting it damaged when it got here.

 

[skulldrinker]

Ive got a 75 in my 2-1/2 car garage and belive me go with the big one one for your size. Otherwise itcwill cycle every 4 mins .

Sent from my SM-N960U using Tapatalk

 

[Bert_]

Ive got a 75 in my 2-1/2 car garage and belive me go with the big one one for your size. Otherwise itcwill cycle every 4 mins .

Sent from my SM-N960U using Tapatalk

Not sure I'm reading this correctly. ^

Short cycling is a problem that happens because the heater is to big. Long cycles are best for comfort and efficiency.

 

[American Locomotive]

As mentioned, most people grossly oversize their heaters. All of the calculators online are usually on the conservative side, erring for safety. A properly sized heater will make you more comfortable and burn less fuel in the long run.

Realistically a properly sized furnace should just about run continuously during the most extreme cold your area will typically experience.

When you oversize your heater, it hurts comfort. You'll quickly warm the air in the building up, making you feel extremely warm very fast. But nothing in the building will be warm yet. The thermostat will cycle off, and then 5 minutes later you get chills as all the cold things in your building **** the heat right out of the air. Furnace turns on again, and this whole process repeats for an hour or two until everything is warmed up.

Where as a smaller, properly sized furnace will run for far longer, heating the air more gradually. It will be constantly bathing the shop with warm air, so you won't get the drastic temperature swings like you would with an oversized furnace.

As far as "heat throw distance": That's just really a made up marketing thing. Just turn on a ceiling fan to circulate air.

Ive got a 75 in my 2-1/2 car garage and belive me go with the big one one for your size. Otherwise itcwill cycle every 4 mins . [/IMG]

That's literally the opposite of how it works. A smaller heater will run for longer and cycle LESS.

 

[Mbrown]

I have a Reznor F100-3 that is giving me some problems. I have replaced gas valve & thermocoupling and it runs good for while and then apparently t-stat calls for heat and burners do not lite and heater kicks out pilot & everything. Any ideas or help would be greatly appreciated.

 

[Jeepnford]

I used some of the online calculators and they were all over the place. I have a 40x60x12 stick built 2x6 walls with batt insulation in walls and about R30 cellulose in ceiling. 6 windows and 2 overhead doors. I live in far Northern Missouri. I ordered a 125k LP unit heater earlier today before I found this thread. Now I’m thinking I oversized it. If I need to downsize I’ll try calling tomorrow and changing it. Thoughts?

 

[u3b3rg33k]

2500 sqft 42k is way too small.

The simple manufacturers chart will get you very close and make an adjustment for climate and insulation.

125k will do the trick. 75k too small 175k too big.

This is funny.
my garage insulation is almost done (half the ceiling left). 5kW/17kBTU heater can make it 65F in there when it's -5F outside. I idle it at 40F to keep things from freezing.

my house furnace stage 1 is 40k in, 80%. never went stage 2 last week.


as for "reheating after opening the doors", well, if all your stuff is 65F, it will not cool off that much if you make a reasonable effort to close the door after you drive out. if you have warmed the slab up by having some air circulation (like a ceiling fan), then even a few minutes of having the door open isn't the end of the world.

 

[Bert_]

as for "reheating after opening the doors", well, if all your stuff is 65F, it will not cool off that much if you make a reasonable effort to close the door after you drive out. if you have warmed the slab up by having some air circulation (like a ceiling fan), then even a few minutes of having the door open isn't the end of the world.

This is the part a lot of people miss. Just because the door gets opened doesn't mean your heater has to do all the work. You could shut the heater off and the air would still warm back up. All your stuff stores a lot of heat.

It's also a good reason to keep the heat on to some extent, at least if you're out there often. Trying to warm up a building full of stuff takes time and a lot of energy. Even a huge heater will be able to warm the air, but everything else will be cold for many hours. So the big heater still doesn't make it comfortable even if the air temp is warm.

 

[zmotorsports]

as for "reheating after opening the doors", well, if all your stuff is 65F, it will not cool off that much if you make a reasonable effort to close the door after you drive out. if you have warmed the slab up by having some air circulation (like a ceiling fan), then even a few minutes of having the door open isn't the end of the world.

This is the part a lot of people miss. Just because the door gets opened doesn't mean your heater has to do all the work. You could shut the heater off and the air would still warm back up. All your stuff stores a lot of heat.

It's also a good reason to keep the heat on to some extent, at least if you're out there often. Trying to warm up a building full of stuff takes time and a lot of energy. Even a huge heater will be able to warm the air, but everything else will be cold for many hours. So the big heater still doesn't make it comfortable even if the air temp is warm.

Agree to both. Most people don't realize that the concrete is the biggest heat sink and focus solely on insulation in walls and ceiling. By keeping the shop at a reasonable temperature with the concrete slab and all contents above and at a mild temperature, it is much less stress on the heating system to bring it up that last bit. Plus like mentioned, opening the door and closing it within a reasonable time frame won't cool everything down to the ambient outdoor temperature and only require a short cycle to warm the air back up.

When I was calculating trying to decide if it was worth the added cost to upgrade from R48 to R60 in the ceiling the payoff just wasn't there because the biggest factor was still the concrete slab.

 

[etbjr]

Heater has arrived! Just need to get it hung and vented, going to have the gas company do the gas run.

 

[olvs]

congrats! it looks good, I found useful service https://www.thefurnaceoutlet.com/ with info about all models and affordable prices. I'm planning to install new hvac unit this year too. Hope I'll find the perfect heater for my house too.