Yet Another "How Should I Heat My Shop" Thread

[atourgates]

I'm having a 44x60 shop (with overhangs on either side making it 60x60 total) built in north Idaho. The gravel pad is done, construction of the shop itself should start in the next few weeks (weather permitting), and I'm hoping to have it insulated (type if insulation TBD), with a concrete pad poured by the end of the summer.

I'm trying to decide what my best bet is to heat it.

The shop will be a combination of woodshop, vehicle parking and recreation space. Particularly on that last count, I expect it'll get more use in the winter than summer. So my plan is to heat it to between 50-60 as a "base temperature" through the winter, and then raise that as needed with either the main heat source (for non-radiant) or a supplemental heat source such as an electric blower or stove (if I go with radiant).

Our average high/low in the coldest months of the year is about 35/24, and we generally get about a week a year when nighttime temps get down to 0F or a bit below, but that's certainly not the norm.

We don't have natural gas (or the option to get it), and right now we pay $0.091/kWh for electricity, and Propane costs us $2.03/gallon. We're planning to add grid-tied solar to the shop's roof at some point (and will be wiring it with that in mind), but that could be several years off. The shop will have its own 200 Amp service.

Insulating, and adding PEX to the 4" concrete floor would add about $10k to the shop's cost, and the boiler and mechanicals from Radiantec would cost right around $4K whether I go with a propane or electric boiler. So, about a $14K initial cost for Radiant.

Using the fuel cost per gallon calculator here, I get the results that per 1-Million BTUs, electricity would cost me $26.67, and propane would cost $26.07.

With that close of a price difference, I'm inclined to go towards an electric boiler since propane would require either a 2nd tank (still researching the rental/installation charge from our utility there), or a 100+ foot run from our existing tank.

The other option I've seen recommended, but don't fully understand, is the option of a ductless mini-split heat pump. It seems like 2x 24,000 BTU units might be enough for the space, which I could get for $4K all-in, considerably cheaper than the initial purchase price of a radiant system.

So, beyond any general advice you might have, I'd love to know:

• Would you recommend forced air, or radiant heat?
• With radiant, is an electric boiler a reasonable option given my propane/electric costs?
• Are there other good options I'm not considering?

 

[bdog]

No one around here has it because it just doesn’t get that cold but everything I have read about in floor heat says it is the way to go in really cold climates. Heat rises so it makes sense. No personal experience but if I ever moved up north that is what I would be looking in to.

 

[atourgates]

Thanks. I've been planning on radiant mostly on the grounds that I've never heard anyone with it say "I really hate it." But I'm totally open to the idea that there could be better options.

 

[The Cobbler]

radiant is slow to respond to changes , so if you keep the temp at say 50° and want to raise it to work in the shop, it takes too long to rise the temperature. so you would be correct in adding supplemental forced air heat . radiant is nice on the feet .

 

[PWC Repair]

I added forced air to my radiant system. It's all I've been running all winter.

 

[hop up]

I would recommend the electric boiler for the floor heat and spray foam insulation to seal the building and increase the R value. I love the idea on solar and with the foam ,heat will hold longer in the building because of its sealing abilities..

 

[Lonnies Performance]

Are you basing your electricity rate on dividing your bill by KW used or using the rate comparison provided with your bill?

When I figured mine out, the electricity cost much more after calculating all the distribution fees, taxes etc. I was closer to $.12/KW.

If using your house rates, keep in mind a separate garage feed will be setup as a commercial rate, which is higher than the base residential rate.

 

[atourgates]

Are you basing your electricity rate on dividing your bill by KW used or using the rate comparison provided with your bill?

When I figured mine out, the electricity cost much more after calculating all the distribution fees, taxes etc. I was closer to $.12/KW.

If using your house rates, keep in mind a separate garage feed will be setup as a commercial rate, which is higher than the base residential rate.

Good point, but yes- that's the actual total of the fees on my electric bill that are variable with the number of kWh used. The other fees are fixed monthly regardless of how many kWh I use.

As far as distribution, we're going with a single pedestal-mount meter next to our distribution box, with a 200A feed that goes to the house, and another that goes to the shop.

There were two reasons for this, one is that our utility charges a $33/mo fee per meter, and the other is that they don't allow you to split a solar generation credit between two meters, even if they're on the same account.

That would mean that when we put solar on the shop's roof, we could only use it to zero-out the shop's electricity use, not our electricity use in the house, which I expect to be much higher.

My goal is to eventually be as close to "Net Zero" as possible, and this is the only setup that'll let us do that with panels mounted on this shop, which will have far-and-away the best exposure for solar on our property.

When I weigh radiant vs. forced air, I guess the big differential is that while everyone seems to love the feel of warm(er) floors in their shop (and I agree with them), forced air would let me heat up and cool-down the shop as needed.

There's nothing in the shop itself that couldn't freeze, so with a forced air system I could theoretically either use automation (let the shop cool down overnight, even below freezing, but come on to make sure the cars are warm'ish in the morning before we leave the house, or in the times we're typically using it) or manually (turn the heat on an hour or two before we plan to go in the shop).

Whereas with radiant, I'd basically be leaving it at a set temperature all winter.

Any thoughts or experience there?

 

[stingry]

First off, I cannot recommend radiant floor heat enough! It is fantastic heat, no noisy heater blowing dust around, warms not only the floor but all objects in the shop, no hot air rising to the ceiling, economical, lower air temperature needed to be comfortable. This is my second year using radiant and would have nothing else.

My shop is 3600 sq ft with 10 ft walls. I use air temp thermostats set at eye level and keep them set at 65 degrees. I work in shirtsleeves even during the nastiest cold windy days. Costs around $100 per month, natural gas and electricity. I am located in Western Nebraska, winter lows in single digits and teens normal, high normally in the high 20s to low 40s.

Your estimate for pex and insulation seems high. Assuming you’re heating the 44x60 section of your shop, This would be 2640 sq ft. 2” XP’s is about $1 per sq ft ($32 for a 4x8 sheet). 1/2 “ oxygen barrier pex is about $.3/ft which is $.30 per sq ft at 12” spacing. This makes $1.30/sq ft. This would be approximately $3500 plus a couple hundred for staples, etc making no more than $4000. Possibly you are adding labor but it is an easy DIY job.

 

[atourgates]

Your estimate for pex and insulation seems high. Assuming you’re heating the 44x60 section of your shop, This would be 2640 sq ft. 2” XP’s is about $1 per sq ft ($32 for a 4x8 sheet). 1/2 “ oxygen barrier pex is about $.3/ft which is $.30 per sq ft at 12” spacing. This makes $1.30/sq ft. This would be approximately $3500 plus a couple hundred for staples, etc making no more than $4000. Possibly you are adding labor but it is an easy DIY job.

Thanks for the feedback. Yes, that cost includes labor. Basically the cost difference in having our pole barn contractor pour a standard concrete floor, vs. one with PEX tubing in it.

Do most people who DIY PEX and insulation install it themselves, and then have a concrete contractor come and pour on top of it?

My quote from Radiatec for PEX and in-floor accessories was about $2,300. , so adding another $2,700 for 2" XPS would be a total of $5K.

I certainly wouldn't mind spending a day setting down some XPS and running some piping if it would save me $5K, I'd just need to find a concrete contractor who's willing to work with me.

 

[stingry]

A friend and I laid the XPS and the pex, easy to do. The pex works best on a warm sunny day. I stapled the pex to the foam board, the supplier of the pex staples loaned me the stapler. I laid 4x6 wire mesh on top of the pex to strengthen the concrete and hold the pex down. The XPS and Pex are extremely durable and will not be hurt by the concrete workers walking on it. Be sure to pressurize the tubing before pouring and have materials to fix leaks if necessary.

I don’t know why the contractor wouldn’t work with you. All they have to do is pour the concrete. No extra labor needed on his part except where the pex exits the floor.

 

[pogrelis97]

I have a 40x60 that I heat with a 5ton electric forced air furnace, I keep it at 40 degrees and turn it to 65 when I'm in there working. in the st Louis area with electric rates at $.06kw I spend $100-$150 to heat it during the winter months. this is 14ft walls, open trusses, and roll insulation between the framing and metal. It could definitely be insulated better but works pretty good for me.

 

[Lonnies Performance]

The other option I've seen recommended, but don't fully understand, is the option of a ductless mini-split heat pump. It seems like 2x 24,000 BTU units might be enough for the space, which I could get for $4K all-in, considerably cheaper than the initial purchase price of a radiant system.

I spent quite a few nights pondering what to do for heat myself.

I ended up with mini-splits for AC, but use them for heat also in addition to my radiant floor heat.

For me it has been cheaper to leave my radiant setting on 50 & use my mini-splits to raise the temp on days I'm working in the garage.

Mini-splits work well if the temperature is in the 30's or above.... they tend to drop in output significantly as you get towards the teens outside & may not function in the single digits, depending on the brand of unit.

A decent mini-split will typically use 1/3 of the power of resistance heat.
Mine pull approx 13A at full load for a 30,000 BTU, whereas that is roughly 10,400 BTU if using straight electric.

I have 6700 SF with 18' ceilings & two 30,000 units have no problem keeping it in the low 60's on the average 30 deg day. I have 4 but typically run 2 unless I need a fast change or it is exceptionally hot/cold out.

You may be very happy with two 24,000 units. It can bring up the temp rather quickly on most days & also cool the place in the summer. Keep in mind these units do not shut off, they run continuously & modulate output as needed. For my needs I cycle them on a schedule as I do not want them on 24x7 wearing themselves out & wasting energy.

As stated in posts above, radiant heat is very nice, but not fast to react when you need to change set points. Another thing I see is, on days with large temperature swings, it is easy to get a temperature overshoot as it warms up outside... meaning you potentially wasted some energy.

 

[Randy in Maine]

I don't have much to add other than to suggest that perhaps you should think about 3 zones. I get my hot water from my house boiler since it is only about 25' away from my shop. I have a little wall mounted Baxi boiler that heats the house and my shop (total of 3 zones) + my domestic hot water.

My shop is only 40'x28'x12' and was built using SIPS so it is pretty well insulated (R-40) and pretty tight. 2" of foam under the 6" of concrete floor and 1/2" pex about every 12". I run 4 250' pex loops. I keep the heat in the shop at 50º which is very comfortable as I move around. I run propane @ $2.49 gallon.

 

[atourgates]

Thanks for everyone's feedback. I spoke with our contractor, and they said they'd be happy to let me lay down the foam and PEX.

In his words, "We don't make our money putting down PEX and foam, and it doesn't make our job any harder if you do it."

For now, I'm having them start construction with the extra 2.5" on the lower wall height that adding PEX and foam would require, with the understanding that if I decided to not go with radiant (unlikely I think), I'd just have to backfill with an extra 2.5" of gravel before they pour the slab.

@Lonnies Performance - your radiant + mini-split setup sounds like more or less the setup I've been envisioning. I'll have to look more into the low-temperature efficiency of mini-splits. During the times that I imagine I'd need them most, our winter temps are fluctuating between about 20-35F. I can't imagine I'd use or need the AC function often, but it'd certainly be a nice option to have if we're doing much out there in the few weeks of really hot weather we get most summers.

 

[d65]

I heat my 300sq ft shop with 7500 of electric heat. It is also insulated. Today it was 35. Outside and shop was 60. Now awaiting the next electric bill.

 

[nsula_country]

I have a 40x60 that I heat with a 5ton electric forced air furnace, I keep it at 40 degrees and turn it to 65 when I'm in there working. in the st Louis area with electric rates at $.06kw I spend $100-$150 to heat it during the winter months. this is 14ft walls, open trusses, and roll insulation between the framing and metal. It could definitely be insulated better but works pretty good for me.

Same setup. 5 Ton Heat Pump with 20kw Electric Furnace. Maintain 50* unless working inside. Can raise to 65*70* in less than 1 hr. 17ft eave, 4/12 pitch, roll insulation.

CT