Radiant heat?

[JCHJ]

I am new to the website and we will build a Barnado in Eastern MT this spring. I am working with a great contractor that, like me, has not installed radiant heat nor minisplits but is more than willing to help me do so. I want to do this install and would like to keep it "KISS", if such applies to radiant heat flooring.

I have done some research and will continue to do so to educate myself and I am curious as to if I need to break two anticipated heating zones into 4 or more (2 each (shop/living area) due to square footage) ? The build will have a 60x40 shop area with the adjoining living area 30x40. The upstairs and downstairs will also utilized mini split units for cooling and added heating capacity. I assume 1/2 pex is appropriate or do I need to go larger? Do you have suggestions on a boiler for the application? The contractor will insulate the footings and slab with 3 inch foam. The build will have 16' 2X6 sidewalls and insulation will be spray foam throughout (other than the slab).

Everything I read provides paralysis by analysis. I am beginning to think it may be much better in the long long run to skip the radiant heat and mini splits for a conventional HVAC system? Thanks in advance for any input and advice

 

[stingry]

Don’t give up on radiant floor heat, it is a very comfortable heat and is economical if properly designed and the space is well insulated. I heat 3600 sq ft with two zones of 1/2 “ PEX, 12 loops of 300’ each spaced 12” apart. I use a 75,000 BTU natural gas water heater as a heat source. I’ve been up and running for 8 years without a single hiccup. I set the temperature and leave it. Good luck with your project.

 

[jack stand]

If any of the living area will be on slab, you'll definitely regret not doing radiant.
It might take 3,4,5 weeks of winter, but the cold will sneak into the slab eventually and even if it's 50-60* that's going to effect the comfort "bigly"! I have a similar build and we added a ductless m/s system primarily for a/c. We discovered their wonderful heating abilities and they extended the time in the shoulder seasons before we fired up the radiant. But before long the slabs temperature just won't let you feel warm despite the air temperature provided by the m/s's.
In your shop (same dimensions and wall height as ours), hot air heating just plain *****! Hot air will rise up and hug the ceiling, and trying to circulate it with ceiling fans.... the effect is a cold draft and opening up an overhead door will cost you hours to recover from especially with mini splits.
We heat our water in a pressurized (closed system) wood boiler with a oil hwh for backup.
I'd recommend a real cast iron boiler, fired by whatever your least expensive btu's are locally and you might as well have a domestic coil and take advantage of that during the winter and I'd recommend adding storage (for the radiant heating)*
Running a boiler just for dhw in the non heating times just doesn't make sense (to me), install a regular hwh for the summer.
We actually have a "Bock" oil hwh that's got a secondary pair of pipes that are for radiant and that's our "backup" and shoulder season radiant source. I only heat the shop slab when the wood boiler is fired up usually a week or so before Christmas.

*one of the economic advantages of radiant is it's designed to be happiest being supplied with 110* water temperatures. That's almost half the temperature of other hot water heating methods.
Added (hot water) storage will economize the boiler and limit it's run time.

 

[Jackfre]

Sounds like a nice space. In your circumstance I’d do the radiant as well with mini-splits for summer and shoulder seasons. Should you choose a cast iron boiler I’d go with Buderus. Their castings are a bit more robust in handling low return water temps, but you still need to pipe for that. You will be in the 80-85% range with cast iron. A wall hung SS boiler is the way I would go. 95% and likely equipped with the outdoor reset which you will need. You can get combi boilers for H & DHW, but before doing so consider the lay-out of the place and the expected use of the DHW. Locating your water heater far from the point of use can drive you nuts. A tankless gas or heat pump water heater will be your best options. There are updated pipe sizing tables for domestic use. Go to the IAPMO site and check them out prior to laying out your pipe systems.

 

[jblnut]

Don’t give up on the radiant floor heat !!!

As mentioned the recovery time when the shop doors are opened is amazing with floor heat. You have a giant concrete battery in the shop just waiting to heat the space again once the door is closed. It’ll be back to temp in far less time than if you’re heating with a forced air system.

I also heat with an outdoor wood boiler and don’t usually fire it up until it’s at risk of freezing. I’ll run the propane backup systems in the shop, house and well house in the “shoulder seasons” to give them some run time and make sure everything works before going into winter.

As far as pipe sizing and zones ….. I have a 54x72x18 shop with two zones. One for the office and bathroom and one for the main shop. There is one loop for the office run and 8? for the shop. I had the pipes spaced 8” for the first 6 runs around the exterior, then 12” for the next 6 runs and 16” apart for the rest of the interior. The office is the same. I also put 4” of insulation down around the outside 8’ and 2” for the rest of the interior of the shop.

I think the max recommended length for 1/2” pex is 300’ but it is also important to keep the runs the same length as each other in the same zone. That way an equal amount of water will be running through each run. My boiler has its own internal circulator and each zone also has its own circulator. The water running through the floor is 90f’ish when the outdoor boiler is running and 120f’ish when the LP boiler is doing the heating.

Whatever your heat source is for the floor make sure to put in at least one extra pex pipe going down into the slab to place a floor thermostat for each zone. I run the shop and house off the floor stats. The house has a forced air furnace for AC and is used to heat the 2nd story. In the house I keep the floor at 69f while the furnace is set to 69f as well on a thermostat upstairs. It works very well.

In both the shop and house I have IBC boilers. They’re what my hvac guy recommended and so far they haven’t given me any issues in 4yrs. They are both available with DHW but I opted to use electric heaters for water as I don’t use the boilers during the winter as the wood stove provides heat for everything.

Mini splits would be a great option to condition the space in the summer and shoulder seasons. You could also do a forded air setup but it’d likely be more $$$ if it isn’t also doing the primary heating. That being said, having a couple backups in cold environments isn’t a bad thing either. I’ve got a buddy in NW Montana and he sent me a picture of a thermometer at -49f a few weeks ago. Gross.

Don’t give up on the infloor heat !!!!!

 

[fitter30]

For the living area there is no better heat than floor radiant. The shop are you going to keep it heated all the time? Type of work in the space and type? Air is easy to heat mass takes time. Set temp back for days at a time mass cools off has to be brought back to temp to be comfortable. There are companies that can run your loads, lay out tubing design on the internet. Minis for cooling i cool and heat 1900 ' with 5 mini wall and 1 ducted. With 2 units 3 heads. Need to watch you tube videos to see how there cleaned and if parts are needed for a repairs might be more than day away. Most efficient way to heat and cool is geothermal can be ground to water or to refrigerate.

 

[jblnut]

Air is easy to heat mass takes time. Set temp back for days at a time mass cools off has to be brought back to temp to be comfortable.

When it’s below -20f outside I’ll set the day temp in the shop up 6f from normal (56f) and it’ll take roughly 3hrs to get there running 90f water through the floor. I’ll set it back down around 10pm when I fill the stove for its evening fill and the shop won’t call for heat until roughly 5am. The floor heats the air up 2f every hour which I think I pretty good when it’s -20f outside.

It’s not a raise the temp to work in there daily sort of deal but I’m doing it to take some load off the boiler overnight so I don’t have to fill it at 11 and 5.

 

[lovetap]

Take the guesswork out of it and do a heat loss calculation (Manual J) and feed it into LoopCAD (free 30 day trial) for system design.