Cost for a garage heated floor system?

[andyvh1959]

When I built my 24x28 shop back in fall of 2019 I put PEX tubing (barrier grade) in the slab. I planned a 30AMP circuit for the electric heat boiler system. But I've not yet bought or installed the boiler/integrator system to connect to the two zone PEX circuit. Researching the systems available at Menards, looks like I'll be spending over $3300 for a 12kw system:

https://www.menards.com/main/plumbing/hydronic-radiant-heat/radiant-heat-boilers/hydro-smart-trade-zones-by-telestats-low-temp-electric-boiler-pro-integrator-panel/hsbp4w-12p-s-mtl/p-1444433729307-c-8519.htm

I'd do the installation myself, since I already have the tubing in the slab and electrical available in the subpanel. So for my shop size is $3300 right for a system sized to keep my shop in the mid 60F range for Zone 1 winter in Wisconsin?

 

[Overboost44]

I can't tell you for sure what you need in WI but for my 26x32, Blue Ridge quoted me a 30k BTU electric boiler with pre-plumbed 3 circuit manifold (1 zone) $4,731. I am in a warmer climate than you are, but hey, it is a datapoint for you. I believe that will be oversized and maybe over priced, but I have not done a load calc on it yet.

 

[PoorUB]

looks like I'll be spending over $3300 for a 12kw system:

You don't need 12kw, roughly 5kw will do fine for that small of an area.

https://www.menards.com/main/plumbi...l/hsbp4w-07p-s-mpl/p-1444433727818-c-8519.htm

 

[andyvh1959]

I tend to agree. I'm not looking to have my shop at 70F in the winter for whatever work I'm doing out there, more like 50F to maybe 60F, especially with heat coming up from the floor. You're in Fargo, I'm in Green Bay, we're both in Zone 1 for winter heating. I bet the calulator for the systems at Menards err well above whats needed. According to the calculator from Menards, calculate BTU needed at 30 BTU (BTU/Sq-Ft/Hr), so for my shop that's 23.5x27.5 (interior) with R19 walls and ceiling, equals 19,388, so round it up to 20,000BTU.

Same calculator at 30 BTU/Sq-Ft/Hr also has watts required per sq-ft/hour, as six to nine. So going at nine watts per sq-ft/hr only comes up to 5,816 watts per hour (5.8kw). So a 7kw system is oversized by 20%. I assume that is for a standard height garage, like mine. If the interior height is higher, like 12' walls maybe increase the wattage by a 1.5 factor, and that bumps it up to 8,724 watts, rounded up to 10kw.

May have to talk to an "expert" at Menards. This 7kw system looks what I need to create the heat for the water-glycol in tubing system:

https://www.menards.com/main/plumbing/hydronic-radiant-heat/radiant-heat-boilers/hydro-smart-trade-zones-by-pumps-low-temp-electric-boiler-pro-integrator-panel/hsbp4w-07p-s-mpl/p-1444433727818-c-8519.htm

Just need to add a hot manifold and return manifold, hoses from the integrator to the manifolds, a thermostat to control the system, and a method to fill/charge the system. The fill system is a bucket of water/glycol, a small 1/2hp pump (fish pond pump):

My 1st question to the person at Menards, "so, have you installed one of these systems yourself?"

 

[PoorUB]

I tend to agree. I'm not looking to have my shop at 70F in the winter for whatever work I'm doing out there, more like 50F to maybe 60F, especially with heat coming up from the floor. You're in Fargo, I'm in Green Bay, we're both in Zone 1 for winter heating. I bet the calulator for the systems at Menards err well above whats needed. According to the calculator from Menards, calculate BTU needed at 30 BTU (BTU/Sq-Ft/Hr), so for my shop that's 23.5x27.5 (interior) with R19 walls and ceiling, equals 19,388, so round it up to 20,000BTU.

Same calculator at 30 BTU/Sq-Ft/Hr also has watts required per sq-ft/hour, as six to nine. So going at nine watts per sq-ft/hr only comes up to 5,816 watts per hour (5.8kw). So a 7kw system is oversized by 20%. I assume that is for a standard height garage, like mine. If the interior height is higher, like 12' walls maybe increase the wattage by a 1.5 factor, and that bumps it up to 8,724 watts, rounded up to 10kw.

May have to talk to an "expert" at Menards. This 7kw system looks what I need to create the heat for the water-glycol in tubing system:

https://www.menards.com/main/plumbing/hydronic-radiant-heat/radiant-heat-boilers/hydro-smart-trade-zones-by-pumps-low-temp-electric-boiler-pro-integrator-panel/hsbp4w-07p-s-mpl/p-1444433727818-c-8519.htm

Just need to add a hot manifold and return manifold, hoses from the integrator to the manifolds, a thermostat to control the system, and a method to fill/charge the system. The fill system is a bucket of water/glycol, a small 1/2hp pump (fish pond pump):

My 1st question to the person at Menards, "so, have you installed one of these systems yourself?"

How many feet of tubing will reflect on the size of boiler. Depending on who you talk to the magic number is around 30 BTU per foot of tubing. If you laid the tubing out at one foot spacing you will have roughly 670 feet of tubing. In round numbers that gets you 20,000 BTU. You can install a 100,000 BTU boiler. but only 20,000 BTU will go into that floor.

Soooo, how many feet of tubing do you have?

"My 1st question to the person at Menards, "so, have you installed one of these systems yourself?"



Sorry, I can't help myself. The guy at Menards would be the last guy I would ask for technical help. They don't exactly hire trained professionals.

I have a buddy across the river in Moorhead with a 900 sqft garage, that heats it with a home made boiler with one 5,000 watt water heater element and it does just fine. If you buy more than a 7,000 watt boiler you are wasting your money.

 

[andyvh1959]

Good points, especially that you and your buddy are in the same zone as I am. I have two zones in my slab, one to the front half and one to the rear half. Pretty sure I spaced the tube runs on 18" C-C spacing, and I started 2' from the OH door on the 24' width end of my shop, 2' in from outside walls. Each zone is at minimum 211' for the number of runs and radii. Two equal zones means 422' x 30BTU = 12,660 BTU. So by that calculation I certainly will not be oversized with a 7kw system by any measure.

Even if I spaced the tubes on 12" C-C, that would get me about 266' per zone, 532' total. 532 x 30 BTU = 15,960 BTU. That sounds like WAY too much for a 24x28 shop. Being frugal as I am I doubt I spaced the tubes on 12" C-C runs.

 

[PoorUB]

So by that calculation I certainly will not be oversized with a 7kw system by any measure.

Yes, the 7kw is way oversized even for that! 7kw is 20,000 BTU, you need about 12,000, but the 7kw is about as small as you will find. If Menards has anything smaller I would get that, 4kw would be about right.

 

[andyvh1959]

Thanks. I'll check if Menards can do a special order for systems smaller than what is shown on the webpage. No need spending more money than I need,.....I am of Dutch heritage so I have to be that way.

 

[BillK]

I cant help you with your selection but I am curious . . . . . you said you have a 30 Amp circuit for the floor heat ? Unless I am wrong with my math that is only good for 7200 W (7.2 KW) and does not take into effect any derating etc.

 

[Burl]

The system at Menards is a HydroSmart system. Talk to those guys. I've had their natural gas system for about 7 years and love it. Those guys are very easy to talk to. Maybe get a better deal buying direct from them.

 

[Dagny]

What's the cost of a kw/hr. in green bay.

 

[andyvh1959]

Yeah, 220v at 30amp is only 6600watts. I'd have to upgrade the circuit to get the capability of 7kw or downsize the system to 5kw. Power cost in WI is around $.18 to $.24 per Kwhr. Average $.21, a 7Kw system would cost $1.47 per hour if running constantly at full output. Net search found heatIng cost per day in the winter is around $7.50 for a well insulated garage.

Hydrosmart shows a 6Kw system rated for 20,478 BTU. By the math 20,478/3.41 = 6,005 watts. My circuit at 30amps is rated to 6600 watts, so by the math it should be good for a 6Kw system, not accounting for any derating. Hydrosmart shows the max amp draw as 25 amp for 220v and requires a 40 amp breaker. Probably a rating factor for the difference. 25amp times 1.5 = 37.5 amp, pretty close to 40 amp, 8ga wire looks right, though it makes no reference to wire length.

Smallest Hydrosmart system is 3Kw, 10,239 BTU. Could be an option, though quite smaller than 5Kw.. Hydrosmart has a 4.5Kw mini boiler for about $1450, plus the integrator panel (pump, expansion tank, valves) for $1760. In components alone $3210.

 

[ipgenie]

I don't know how many feet of tubing I have but my home has 2800sq ft of heated floor in the house and 730 in the garage. I'm in Idaho and heat it most nights during off peak hours with two 4500W heating elements in a residential water heater. It's wired to run both elements at the same time.

If it gets below zero for long the water heater can't keep up and the propane boiler will fire up as needed to supliment. Above zero it's enough to keep the house comfortably at about 70.

You'll have to figure out water temps that work for your space. Higher temps will transfer more BTUs but a good rule of thumb is to feed 140 degrees or less into the slab. Outdoor offset can automate that feed temp higher or lower based on the outside temp to help run more economical.

Maybe that's helpful even though it's not really a good comparison as far as Sq ft and size.

 

[Stuart in MN]

I have a friend here in Minneapolis who uses a domestic water heater for the in floor heat in his garage. A boiler is recommended but it works for him.

 

[mike93lx]

Yeah, 220v at 30amp is only 6600watts. I'd have to upgrade the circuit to get the capability of 7kw or downsize the system to 5kw. Power cost in WI is around $.18 to $.24 per Kwhr. Average $.21, a 7Kw system would cost $1.47 per hour if running constantly at full output. Net search found heatIng cost per day in the winter is around $7.50 for a well insulated garage.

Hydrosmart shows a 6Kw system rated for 20,478 BTU. By the math 20,478/3.41 = 6,005 watts. My circuit at 30amps is rated to 6600 watts, so by the math it should be good for a 6Kw system, not accounting for any derating. Hydrosmart shows the max amp draw as 25 amp for 220v and requires a 40 amp breaker. Probably a rating factor for the difference. 25amp times 1.5 = 37.5 amp, pretty close to 40 amp, 8ga wire looks right, though it makes no reference to wire length.

Smallest Hydrosmart system is 3Kw, 10,239 BTU. Could be an option, though quite smaller than 5Kw.. Hydrosmart has a 4.5Kw mini boiler for about $1450, plus the integrator panel (pump, expansion tank, valves) for $1760. In components alone $3210.

Good thing we have 240v service in the US

You need to derate by 80% as this will run for long periods of time. So a 30a 240v circuit would be good for about 5.8kw

 

[jblnut]

I have a 120kbtu modulating LP IBC boiler in my 54x72x18 farm shop and even on the coldest days it never went above 60,000btus from what I saw when I was watching. Tracking LP usage the first two years I used it put the shop at around a 15btu/sqft of needed heat.

I put in an outdoor wood stove and love it. It heats the house, shop and my little well house using around 22-25cord of softwoods a year. You could put in an outdoor stove and get "free" heat !! More chainsaws, wood splitters, logging gear, trailers, skidloaders, grapple buckets and all the other fun stuff that makes burning wood fun and "free" lol. We love it but it isn't for everyone.

My installer guy for the shop HVAC setup wanted to put in a 200,000btu boiler in the shop and I pumped the brakes on that. It's incredibly well insulated and I thought 30btu/sqft was more than plenty already. Turns out I was correct for once lol

I know of quite a few shops up here heated with water heaters. One in particular is close to 15,000sq/ft. They have a pair of large water heaters in a few places in the shop that provide heat to each zone so they didn't need to do large home run runs back to a central point. That particular shop was built in the mid 90's so things were a little more cowboy than they are now but it's been working great. I seriously thought about a water heater setup for my shop but decided against it as I didn't want the space taken up plus I wanted to do a wood stove in the future and I thought it'd be easier to connect the systems with a LP Boiler vs a water heater. Looking back I wish I'd have done a water heater but oh well.

 

[finn]

I have a friend here in Minneapolis who uses a domestic water heater for the in floor heat in his garage. A boiler is recommended but it works for him.

A water heater, sometimes used and repurposed is a pretty common low buck approach. It’s not the recommended heat source, but quite a few seem to use one with no bad reports.

 

[andyvh1959]

So if you use a HW heater, do you depend on heat transfer to move the fluid or use a low flow pump,

 

[Stuart in MN]

So if you use a HW heater, do you depend on heat transfer to move the fluid or use a low flow pump,

My friend's system does use a pump. The whole thing is pretty simple, a thermostat controls a relay that operates the pump, and the water heater just runs off its internal thermostat.

 

[Stuart in MN]

I have a 120kbtu modulating LP IBC boiler in my 54x72x18 farm shop and even on the coldest days it never went above 60,000btus from what I saw when I was watching. Tracking LP usage the first two years I used it put the shop at around a 15btu/sqft of needed heat.

I put in an outdoor wood stove and love it. It heats the house, shop and my little well house using around 22-25cord of softwoods a year. You could put in an outdoor stove and get "free" heat !! More chainsaws, wood splitters, logging gear, trailers, skidloaders, grapple buckets and all the other fun stuff that makes burning wood fun and "free" lol. We love it but it isn't for everyone.

My installer guy for the shop HVAC setup wanted to put in a 200,000btu boiler in the shop and I pumped the brakes on that. It's incredibly well insulated and I thought 30btu/sqft was more than plenty already. Turns out I was correct for once lol

I know of quite a few shops up here heated with water heaters. One in particular is close to 15,000sq/ft. They have a pair of large water heaters in a few places in the shop that provide heat to each zone so they didn't need to do large home run runs back to a central point. That particular shop was built in the mid 90's so things were a little more cowboy than they are now but it's been working great. I seriously thought about a water heater setup for my shop but decided against it as I didn't want the space taken up plus I wanted to do a wood stove in the future and I thought it'd be easier to connect the systems with a LP Boiler vs a water heater. Looking back I wish I'd have done a water heater but oh well.

I watch the Dig-Drive-DIY YouTube channel. He's in NE Indiana but has a wood boiler that heats his house and shop that came from Crown Royal Stoves in International Falls, MN. Last fall he replaced the existing boiler that had been in use for quite a few years with their latest version which is quite a bit more efficient. He made several videos about the install including a visit to their factory, it was pretty interesting.

 

[andyvh1959]

I might go the route of a small (30gal or smaller) hot water heater along with the integrator panel from Hydrosmart. A small HW heater is less than $500 versus $1800+ for the Hydrosmart boiler system and easier to tailor to the wattage needed and power avaiable.

The Hydrosmart boiler is certainly smaller, mounts easily on the wall, is basically an on demand local water heater, but costs a lot more, and would have to cycle more often. A small, 30 gallon hot water heater creates a larger volume of hot water so it may actually make a small system cycle less because more system water is heated and pumped through the circuit. There is about four gallons of water in the tubing system, so a 30 gallon hot water heater would have almost eight times the tubing volume of water/glycol heated to say 120F. I'd assume the HYdrosmart boiler is less than two gallons of volume.

Now the Hydrosmart boiler creates higher heat, above 140F but holds a lot less of it in the circuit. Also, a small hot water heater would have to be compatible with 50/50 water-glycol. From previous posts it reads like a HW heater is a good application and easy to source. Maybe a brand name like Rheem. Would have to be flow rated to match the pump, floor or wall mount. Maybe that's the cost difference. A Hydrosmart boiler may be near constant duty cycle rated because it holds less than two gallons of fluid. In cold temps it'd have to run/cycle a lot more than a larger volume of hot fluid. Whereas a small HW heater does not have to run constant duty because it creates a larger volume of hot fluid to cycle less. Also, a tank volume of 10 to 30 gallons would allow for lower wattage because the larger volume of hot fluid would "buffer" the cycle time from when the thermostat turns the heater on.

https://www.homedepot.com/p/Rheem-10-Gal-208-Volt-6-kW-1-Phase-Point-of-Use-Commercial-Electric-Water-Heater-EGSP10-208-Volt-6kW-POU/312272992

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[jblnut]

I watch the Dig-Drive-DIY YouTube channel. He's in NE Indiana but has a wood boiler that heats his house and shop that came from Crown Royal Stoves in International Falls, MN. Last fall he replaced the existing boiler that had been in use for quite a few years with their latest version which is quite a bit more efficient. He made several videos about the install including a visit to their factory, it was pretty interesting.

I also have a Crown Royal stove but it’s more similar to his old stove than the his new one. The gasification stoves aren’t real bonkers about burning sappy wood or wood that isn’t well seasoned. The MultiPass Series (what I have) is more like an old conventional stove but has a few features that help with efficiency. One day I may move to a gasification stove but so far so good with this one.

I also like Dig Drive DIY. He’s a genuine dude hat makes nice content.

I might go the route of a small (30gal or smaller) hot water heater along with the integrator panel from Hydrosmart. A small HW heater is less than $500 versus $1800+ for the Hydrosmart boiler system and easier to tailor to the wattage needed and power avaiable.

The Hydrosmart boiler is certainly smaller, mounts easily on the wall, is basically an on demand local water heater, but costs a lot more, and would have to cycle more often. A small, 30 gallon hot water heater creates a larger volume of hot water so it may actually make a small system cycle less because more system water is heated and pumped through the circuit. There is about four gallons of water in the tubing system, so a 30 gallon hot water heater would have almost eight times the tubing volume of water/glycol heated to say 120F. I'd assume the HYdrosmart boiler is less than two gallons of volume.

Now the Hydrosmart boiler creates higher heat, above 140F but holds a lot less of it in the circuit. Also, a small hot water heater would have to be compatible with 50/50 water-glycol. From previous posts it reads like a HW heater is a good application and easy to source. Maybe a brand name like Rheem. Would have to be flow rated to match the pump, floor or wall mount. Maybe that's the cost difference. A Hydrosmart boiler may be near constant duty cycle rated because it holds less than two gallons of fluid. In cold temps it'd have to run/cycle a lot more than a larger volume of hot fluid. Whereas a small HW heater does not have to run constant duty because it creates a larger volume of hot fluid to cycle less. Also, a tank volume of 10 to 30 gallons would allow for lower wattage because the larger volume of hot fluid would "buffer" the cycle time from when the thermostat turns the heater on.

https://www.homedepot.com/p/Rheem-10-Gal-208-Volt-6-kW-1-Phase-Point-of-Use-Commercial-Electric-Water-Heater-EGSP10-208-Volt-6kW-POU/312272992

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Having 30gal of storage vs a small on demand heater is the same concept of an outdoor wood stove. I have over 400gal in my wood stove circuit and it’ll heat it all up when needed.

Also …… it’s just a water heater. Not sure why you’d need a hot water heater. It’s already hot