Hydronic driveway circulator pump advice

[MIDan]

Hello I have read through a few of the posts on hydronic systems and done my own but am still a little lost and looking for advice. The first owner of my house put in the start of a hydronic heated driveway system. The garage has a manifold with 4 loops for a driveway that is about 240 sq feet. I have pressure tested the system so I know that it holds pressure but the system is missing circulator pumps and an expansion tank. I am going to describe the setup and then include some photos:
There is a 50 gal Powerflex power vent water heater. The water heater is about 6 feet from the heat exchanger, two copper pipes come off of the side of the water heater run up to the ceiling and then over to the heat exchanger so close to 12 feet of 1/2 inch copper pipe. After the heat exchanger there are a red and blue pex pipe that run to a wall 12 feet away then into the garage where they are wrapped in some foam insulation and travel along the garage wall to a 4 zone manifold. So I've been trying to do the math and calculate gpm and head loss, my work shows a gpm of 7.2 on the manifold side with a head loss of about 10 but I really don't know if that is right. I'm also not sure how to figure out gpm and head loss for the water heater loop, and I have no idea how to figure out how big of an expansion tank I need. I can get some grundfus alpha1 15-55fr for $90 each and I think that will give me what I need but I'm not sure.
All of my photos are too big to post but I can share a link to them I think.

Driveway heating

9 new items added to shared album

photos.app.goo.gl

Thanks in advance for any help
Dan

 

[Breplum]

Just FYI, you have a low effeciency (80%) furnace and a lower effeciency (70%ish tank water heater).
You will be better off upgrading to 96% AFUE some day, and, sooner is better...you will get a good return on that investment.
You might have better luck at HeatingHelp.com The Wall...but doubt you'll get fully fleshed out solution.
I would seriously recommend hiring a licensed pro.

 

[Sponsor]

 

[Fitter30]

Drive is 12' x 20'? snowmelt loops 6" centers 150 btu's sq ft

Radiant Snowmelt Systems at Work

Snowmelting employs tubing buried outside to melt ice and snow, keeping driveways, sidewalks, hospital and senior housing entry areas, helicopter pads, and delivery ramps free of ice and snow.

www.pmengineer.com

 

[Jadnashua]

Snowmelting can be installed with a few different levels of effectiveness. At the top of the heap is one with enough heat to keep the surface from any snow or ice, regardless of the temperature and rate of fall of precipitation. That tends to get used on sidewalks and maybe helicopter landing pads where it is critical to always have safe access. Then, you have a system that can keep up with a moderate snowfall, but at the higher end, will take a bit of time to melt off the remainder. At the bottom of the scheme, you have one that can melt the snow, but it takes time, regardless of the snowfall rate. All of them should have melting at the base which can facilitate plowing or shoveling to augment the end result if desired or needed.

The outside loop should have antifreeze in it with enough capacity to prevent freezing at your worst temperature expectation. Snowmelt on asphalt can be problematic, but works better in concrete. The amount of heat you need is based on which level of system you want to implement and whether the surface has any insulation underneath to isolate it from the ground.

One big thing is to ensure that the meltoff has somewhere to go that won't create a safety hazard...melting all of your driveway and having it refreeze when it hits the roadway can have both safety and liability issues. Suitable drains may need to be included in your design and depending on their depth, may need heating to make sure they don't just fill up with ice.

Note, the use of antifreeze will decrease the ability of the fluid to transfer heat, so it becomes about 10% less efficient at that versus when using pure water.