Another cold climate home with hydronic piping in exterior walls. Who does this??

PeterOrion

Hello Folks, I have a similar situation in Climate Zone 6 / Central NY for a slab on grade cape with distribution running up to the attic knee wall areas and then down a few exterior wall bays. We are a weatherization agency looking to cut down the hemorrhage of natural gas usage with insulation and air sealing measures. Others have warned about insulating the wall bays with piping arguing that hot water freezes faster that cold. An internet query offers that is more the case with warm or ambient temp water and not significantly faster than if the water is cold or hot. It seems more sensible to prepare the client to shut down and drain the system in the event of an extended power outage rather than the permanent costs associated with the degraded distribution efficiency. In short, we are weighing not insulating the wall bays with piping vs. changing the system to glycol. Any feedback would be greatly appreciated.

DCContrarian

In general, the efficiency hit of glycol is way overstated. It doesn't make your burner burn any less efficiently. What it means is that slightly more fluid needs to be pumped to get the same heat transfer. Your system will have a slightly lower maximum output, but unless it's undersized that shouldn't be an issue. The circulator pump will consume slightly more energy having to pump more fluid but that's the extent of the energy penalty.

Steamhead

I would think that if the wall bay insulation is placed between the outside wall surface and the piping, then the piping would remain at or near the indoor ambient temperature, so it would not be much more vulnerable to freezing than any other interior piping.

pecmsg

hot water does NOT freeze quicker!

mattmia2

How much work are you doing and how much piping is in the exterior wall? Perhaps moving it will solve numerous problems. Glycol needs maintenance of the inhibitor. Placing the insulation between the exterior and the piping would seem to be an amount of work where re-routing the piping would be a negligible additional step.

LRCCBJ

It is an ongoing fallacy that hot water freezes faster than cold water. Personally, I believe the fallacy is developed from the fact that hot water cools faster than cold water. People without any intelligence then extrapolate that hot water must freeze faster because its temperature is falling faster. Nothing could be further from the truth.

With regard to piping in the exterior walls, I restored one house to get the iron piping out of the living space. The look is less than desirable.

Since the wall was open, I utilized 2" styrofoam, 14.5" width for the entire height of the bay. The styrofoam was cut slightly large so it was pressing on the studs without any gaps. The copper lives in the 1.5" space between the sheetrock and the styrofoam. The copper is not insulated and the intention is for the line to warm the fairly small space left in the bay.

The system works perfectly down to -3F. However, it has never suffered a power outage at that temperature to verify that it would be successful under those conditions. I highly doubt that even interior piping will survive more than 24 hours in the event of an extended power outage at -3F ambient.

hot_rod

Piping in an outside wall is never a good idea. Pipe insulation limits the loss, but it is all about the delta between the pipe wall temperature and the space around it.

These charts show the pipe loss differences between bare and insulated copper.

Two things about glycol, it has a lower heat capacity, higher viscosity

So a 40% mix at 120F temperature would require about 8% higher flow rate, maybe 15% higher head. In some cases you may need to increase pump size.

In a clean system, hydronic glycol should last 15- 20 years. Testing every few years will assure it stays in good condition.

In some cases glycol is the best answer for 100% freeze protection if piping is susceptible to freezing and extended power outages.

I've seen fin tube baseboard freeze inside the building, when there was air leakage around the framing. So the building envelop has a lot to do with freeze potential.

Screenshot 2024-10-03 at 1.34.15 PM.png

delcrossv

"I've seen fin tube baseboard freeze inside the building, when there was air leakage around the framing. So the building envelop has a lot to do with freeze potential."

Just replaced some where the fin tube was between (leaky) windows and a curtain which trapped cold air in the gap.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1812877#Comment_1812877

The seal around the bottom of the wall and the plate and the floor is usually poor. pipes usually freeze not when it is the coldest but when it is fairly cold and there is a wind to push air in through openings in the building that are close to a pipe.

hot_rod

I did a lot of pipe thawing back when we had the shop in the mountains
Infiltration was the biggest cause of freeze up. Windy days at below freezing conditions, we were always frozen pipe days. That’s when I got sold on spray foam, even a 1/2” layer with batts over it would seal a building against infiltration.

Underground piping froze when we had years with little snowfall to insulate the yards

CBRob

@hot_rod

In Crested Butte way back in the 70s and 80s they had mains and waterlines to homes that would freeze on low snow years. The solution used to be a bonfire in the yard over the pipe until it thawed.

PeterOrion

Wow, I'm truly grateful for all the great responses the post garnered. Thank you all so much for taking the time. You have collectively given enough insights to form a plan.