Garage Heater - Pex or Copper

Gary_7

I'm planning to install a Modine HHD45 Hot Water garage heater. I'm planning to run the pipes/tubing perpendicular to the joists due to the installation location. I will install the pipes through the joists so that in addition to pipe insulation, the joist bay insulation will help keep the pipes from freezing and reduce pipe heat loss. Looks like it could be a tough job with copper, not sure if i'd be able to flex the copper pipe enough to get it to go through the holes in the joists without damaging the copper pipe.

Question #1: If I use pex instead, about an 20' run, would I need to install an expansion loop on each side (boiler and heater)? Or is one side enough? I expect up to 210 degree F water flowing thru the tubing. Too hot for Pex?

Question #2: The installation manual doesn't specify whether to use 1/2" or 3/4" but the connections on the unit are 1/2" and the connections at my boiler are 3/4". With an 18-20' run, would I lose too many btus with 1/2" pex tubing or copper pipe? Is there anything to gain by using 3/4" over the 1/2"?

thx in advance
Gary

hot_rod

3/4” Pex would be my choice. Why 210 degrees?
The pex will expand as it warms, so allow for that when you pulled through drilled holes. A 1-3/8 hole will accept the plastic isolators or pipe insulation.

An expansion arm on either end will take up the small amount of linear expansion

Jamie Hall

Ah... um. If you plan on putting holes in the joists, there are very definite limits on where they can be safely located in the joist, and how big they can be. Not within two inches of the top or bottom, not over a third of the depth of the joist, not closer together than three hole diameters, located only in the middle third of the length... for starters.

hot_rod

If you have the web type I joist a 1-1/2” hole can be drilled anywhere in the web, or use the pre-punched holes.
Most building code books have hole and notch charts in them, for structural 2X lumber

Ironman

Most pex is rated for 180*. Why do you need 210* on a hydronic system? That’s getting way too close to the boiling point.

Also: you would have to use O2 barrier pex.

pecmsg

I hope this garage doesn’t get below freezing. 

Gary_7

Thx for the comments/questions. Here are some answers.
- WI joists so holes won't be an issue. Will install web stiffeners if necessary.
- Up to 210 degrees because that's what my boiler gets up to (I think). I think it shuts down at 190 or when return gets up to 170. System runs under a little pressure so boiling point should be higher than 212. I'm also not interested in installing a tempering valve and I don't think that would work with my boiler anyway. (EK1)
- Yes the garage will get below freezing occasionally but I plan to run it on a t-stat at about 40.

MaxMercy

Insulation doesn't prevent freezing if there's no heat source. If your pipes will run along a wall or ceiling with a heat source behind it, then insulate between your pipes and the unheated area - do not insulate between the pipes and the wall or ceiling.

If there is no wall or ceiling with heat on the other side, your insulation won't help if the boiler quits. Eventually, the pipes will freeze if the area is freezing.

pecmsg

Gary_7 said:

Thx for the comments/questions. Here are some answers.
- WI joists so holes won't be an issue. Will install web stiffeners if necessary.
- Up to 210 degrees because that's what my boiler gets up to (I think). I think it shuts down at 190 or when return gets up to 170. System runs under a little pressure so boiling point should be higher than 212. I'm also not interested in installing a tempering valve and I don't think that would work with my boiler anyway. (EK1)
- Yes the garage will get below freezing occasionally but I plan to run it on a t-stat at about 40.

Better have Glycol in that system.

Gary_7

I'm going to stay away from glycol because of the btu output reduction.
Yes if the boiler fails or I lose electric I may have a problem, but thats the same risk we have with the home also.
Am considering putting in a recirculating pump to keep the water moving at low temps.

pecmsg

Do a lot more research than.

MikeL_2

  Operating temps near or above 200°F can fluctuate and be dangerous. Inaccurate gauges, latent heat, circulator failure, and pressure drop can all contribute to water flashing to steam......
   

Daveinscranton

Just a thought.  I am not a pro.  Just old.

 I leave as much infrastructure exposed as possible.  A pipe/fitting you can get to will not leak.  One you can see won’t leak either.  Murphy’s Law type of thing.  If the pipe needs insulation, then it gets insulation.  Too many times taking out ceilings, sheet rock etc.  

Building inspector went batty looking at my laundry room.  Surface mounted plumbing.  It was legal and within code.  He could not believe someone would do that in a new house.  He was still talking to himself as he drove away.  Everything in the basement is exposed.  It doesn’t leak either.  If I covered it, it would.  Nature of life I think.

Nothing has leaked.

MaxMercy

Daveinscranton said:

If I covered it, it would.  Nature of life I think.

Nothing has leaked.

Don't own a Colonial then!!

hot_rod

I would certainly look into lowering the operating temperature of the boiler. The team from EK hangs around here, certainly they could shed some light on the settings.

jringel

Thank you for your post @Gary_7 .
The best and most simple approach is to install the zone as copper, nothing else is required.
If PEX is required and the operating temperature of the unit heater loop can exceed the PEX maximum temperature ratings, then one solution is to add a thermostat (Aquastat) like an L4006A1017/U on the supply pipe feeding the zone.
The thermostat can open on rise at an appropriate temperature for the PEX to operate (maybe 180°F open, with a 5°-30°F differential). This would break the thermostat call to the Energy Manager for the PEX Zone and turn off the burner, but if it were the only zone calling, it would purge the heat remaining in the boiler and continue to operate the unit heater – the thermostat call and burner will come back on when the temperature drops. If other zones were calling, the boiler temperature would likely remain lower most of the time, and the thermostat will provide PEX overheating protection. You may need some testing to pick the appropriate open on rise temperature (and differential) as there may be some delay to respond, and to accommodate potential coast up in temperature after the burner turns off.
30% glycol is worthwhile for garage freeze protection. The reduced heat transfer can be offset with a higher PEX circulator flow rate (if a zone circulator) and higher unit heater fan speed, so install the larger PEX tubing for both output. Having enough flow through the zone will keep the supply and return temperatures closer together and minimize supply temperature creep.

Gary_7

Thx John for the info.

I was leaning toward copper over the pex but I have re-evaluated and decided not to do it. It is a large expense and a headache to do the job and since I would not be using it on a daily basis I think I'm just going to install an electric heater for the few times that it will get used.

By far you're response is the most in depth and helpful reply.

Thx
Gary