Radiator-Baseboard-Piping Complexities

DJDrew

Questions for the wall….

We are in the midst of an addition over finished space and we are working to add heat. The construction contractor has a mini-split going in, but we only want to use that for cooling in the summer. The rest of our house has hot-water radiators and panel radiators, all piped with individual supply/returns. Ideally we'd like to use the existing system for heat in the new space, there is excess capacity — and the boiler usually operates in the 130-140 supply range. (For reference, the new room is 12x12 with a cathedral ceiling…~3800 btu calculation.)

We have access to similar-style radiators that are in the rest of the house, but because of the way the framing was done, there are a few key LVL beams in the way, which we are being told no holes should be drilled in those beams, which complicates running the lines for a radiator.

Multiple contractors have told us we have two options.

1. First option would be to do a fair amount of more surgery on the house and open up another wall and ceiling to bypass the LVL and be able to use Iron, Copper or Heating Pex for a new radiator line down to the original cast iron lines.
2. Second option would be to use an existing plumbing and electrical chase that is on the wrong side of the LVL where the heat needs to be, but poke through the wall and install 12-15' of "Low-Temperature" baseboard. Since the connections would poke through the wall and run the perimeter, the LVL would not be in the way and they'd be able to fish Heating Pex up the existing chase. There was debate if it would need to be zoned separate or just a TRV installed on the baseboard. They acknowledge the existing cast-iron would radiate for much longer, but the baseboard would be in new-construction that is heavily insulated and hold heat better than the rest of the uninsulated house, so they were more concerned with overheating during the long heat-on cycles.

The BTU heat-loss math works out for the low-temp baseboard and would be a cleaner install today. However, would we notice a difference in the heat and regret not making more of a mess today?

Any Suggestions or Thoughts?

Jamie Hall

Pity someone didn't think of where the pipes had to go when the framing was planned… there had to be a way.

However, you run what you brung, and in this situation I'd go with the "low temperature" baseboard. Yes, it will respond differently. It will heat faster and cool down faster. The low temperature part simply means that for a given length and water temperature, it should put out more heat than regular baseboard — and either it or regular would respond faster.

But… it will respond faster, but does that have to be a problem? No, it doesn't. Set up your boiler, if you can, to provide just hot enough water so that the whole house is circulating all the time, rather than on/off. You don't mention what the boiler is, but if it's a mod/con with outdoor reset, that's just a matter of changing the curve. If it isn't, then I'd seriously consider piping the new baseboard as a seconday loop off the main system, with it's own pump — and a mixing valve recycling some of the return to lower the temperature, ideally with that mixing valve on an outdoor reset. Then leave the baseboard running all the time (or most of it anyway) with the boiler responding to its aquastat as it normally does to give the whole thing a shot of heat when needed.

hot_rod

IMG_9059.jpeg

get the brand name off the LVL and go to their website for a hole drilling guide. Pex lines generally need a 1-3/8” hole you may be able to drill a few small holes like that.

DJDrew

Thanks @Jamie Hall - we were looking at some piping modifications around the boiler to achieve some of those suggestions too. Insisting they run the pex lines back to the boiler vs tying in with the rest of the radiators sounds like a reasonable request then to future proof our options if we go with the baseboard.

Thanks @hot_rod - I think we were advised to not drill the one LVL since it is rear-beam supporting the floor joists for a cantilevered section.

DJDrew

So based off of @hot_rod's suggestion, my contractor and I pressed the LVL manufacturer and an engineer to study the hole issue further and we got permission for two 1-1/4" holes in the middle section of the beam. So it looks like we will be able to get supply/return piping to that section of the addition via a roundabout way - its not direct or open enough for feeding iron or copper, but should be able to fish O2 barrier pex. (FWIW, I kept pressing them since I was worried about baseboard acting differently compared to the whole house and putting it on a separate zone would probably have short-cycled the basic cast-iron boiler that is installed.)

Question on pex sizing though: Most radiators in the house are 3/4" iron lines taped off a much larger supply/return that run the permitter of the house. I know I can snake 3/4" pex up the existing walls and through the new space for the radiator. Is it worth the hassle of trying to snake 1" pex? Would I run into flow-resistance issue using 3/4" pex vs the rest of the house on 3/4" iron? My goal would be to have no pex fittings aside from when it transitions back to black iron floor nipple and pops back up into the room.

hot_rod

You mentioned a 3800 btu/ hr. load in the new room?

3/4 pex at 4 gpm gets you 40,000 btu/hr.

Here is what a 3/4 pex loop 100' long, 4 ells 4 couplings, looks like.

So a good match for your radiator, with under 4 fps velocity, reasonable head.

If you know the exact length and how many fittings you will use. Go to the free calculator at ppi website, plug in actual numbers. Plastic Pipe Institute.

Screenshot 2024-12-11 at 3.07.15 PM.png

Here is an example of an engineered LVL fix. After the fact repair 😚

LVL repair.png

DJDrew

Thanks @hot_rod!

One other quick question, when transitioning the pex into the radiator valve… would best practice be to mount a drop ear ell with female threads under the floor and then attach a steel nipple to come out the floor? Do I need to worry about leaks on the threads below the floor? (There will eventually be a finished ceiling.) Or would I be better to transition the pex to copper and put a threaded end on the copper at floor level to receive the TRV valve?

Anyone have any suggestions or best practice on the transition? I really don't want to "see" the pex.

hot_rod

there are sleeves available to cover the pex where it is exposed.

If you can trust a blind threaded connect that will work also.
It comes down to your confidence level with the connections

What is below it ?😉

DJDrew

Good point @hot_rod, perhaps if I practice and had an inspection camera to poke around I'd trust a blind connection. Not sure my wife would want radiator water dripping in her coffee though.

How goofy would using a copper stub out be in this situation? I could secure the connection easily, pressure test, and then come back and put the valves on when it's time… Is that acceptable? Or will I be chided by others for that?

https://pexuniverse.com/sioux-chief-630x348e-copper-stub-out-elbow

hot_rod

I like the copper stub idea best. Fairly durable, easy to connect to, and the same trim covers will fit over it if you want chrome or?

IMG_9184.jpeg

DJDrew

Thanks so much!

Kaos

If your main heat loop is gravity feed modified to pumped, all the plumbing to the existing rads would be very low restriction. This means very small pressure drop between the supply and return so adding another parallel zone with long runs of pipes might not get you much flor through there.

I think the simpler option is to install a small circulator and run 1/2" pex all the way to your new rad. Use one of the chrome sleeves to cover. If you use one of the ECM pumps on low speed, it will only consume a couple of watts and you can leave it running 24/7.