Replacing hot water baseboards with PEX

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Hello,

I have two bedrooms I'm looking to remodel. Its a 1920's bungalow, which I suspect had no heating when it was built, was probably used as a summer-only house. It appears that when heat was added sometime later, they did it the "easy" way and just ran 3/4 copper with baseboard radiators all along the perimeter of the house right through the walls with little regard for how the piping actually looked. So I have a lot of old/aging enclosures all around the perimeter of the rooms.

Based upon a few heat calculators, I believe there are too many feet of radiators, I'd like to put the proper length in, and remove the excess. (This in addition to insulating the room well of course). These rooms do tend to feel warmer than the newer rooms which do have proper insulation, leading me to believe that there is too much heat output in the older rooms.

From researching on here, it seems that I need to buy special PEX that has an oxygen barrier in it. I'd like to hide the piping in the studs of the wall where it's not needed for the actual radiators.

I could do it with copper, but I think I'd end up with a ton of joints that I would need to sweat due to fitting the pipes into the studs. I have no problem with sweating pipes, I'm not a plumber, but relatively handy DIY, but if it's only $100 or so to make the job quick and simple, I'm for it.

Not to mention, it is winter time, and I can't afford to have my boiler down for more than a few hours. I have one zone for the whole house.

I don't have a pex tool or fittings currently. I've only used the quick connect (sharkbite type) fittings before.

Basically my question is an overview of how to do this and what to look out for?

Things like..

What tool and fittings to buy? (I'd assume there is low confidence in the push-on type for hot water heat if they will even work with Oxygen barrier pex)
How to secure the pex in the wall to account for heating/contraction. (I'd assume I'd just drill 1" holes through the centers of the studs, leave a loop for expansion, and put nail plates over it. )
How to insulate the pex (exterior wall - Just put half the fiberglass on each side of the pipe?).

Thank you in advace.
 
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Reach4

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How to insulate the pex (exterior wall - Just put half the fiberglass on each side of the pipe?).
Put the PEX on the inside of the insulation.

I would do some searching for past posts that include "PEX A" "PEX B" to get you started.
 

BadgerBoilerMN

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Stay out of the outside walls. Barrier PEX up through the floor to your new Panel Radiators, one under each window, will give you individual room control and most of your wall space back.

Some will use the PAP pipe for this (there is no better oxygen barrier semi-flexible hydronic pipe, be it Mr. PEX, Uponor or Viega) but I normally use a standard barrier PEX in 1/2" home-runs.

A room-by-room heat load analysis would be in order or you can do like the last guy and WAG it.

What is the heat source?
 
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I have an older gas fired boiler. I can check the BTU rating when I get home later.

Those wall panel radiators are interesting. Coming up from the floor is almost a no-go. It's very hard to get access in that part of the house from the crawlspace, and I wouldn't be able to get the piping over to the furnace room. Coming down from the attic might be an option. But I would still need to re-connect the rest of the single loop for the rest of the house, and not sure how that would all connect back at the boiler. Seems like I might need to add two additional zones?
 

Dana

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Don't just rip out heat emitters willy-nilly. The total radiation has to be sized for the output of the boiler, as well as for the heat load of the house or it'll short-cycle into lower efficiency and an earlier grave. If you're replacing the scrap iron beast with condensing equipment the extra emitter capacity allows you to run cooler boiler temps for highest efficiency.

With condensing equipment there's almost no such thing as "...too many feet of radiators...", but with any type of boiler there such a thing as improper room-to-room balance, as wall as too LITTLE radiation. If you start breaking it up into zones you make the boiler-output to heat-emitter capacity problem even worse, since the radiation on each individual zone needs to be able to handle the bulk of the boiler's output to prevent short cycling.

Are these cast-iron baseboard radiators, fin-tube baseboard,or something else?

Size the room radiation proportionally to the room loads, with maybe 15-25% more radiation on the last (coolest water end) of the loop than on the first (warmest water end). To get there in a quick & dirty napkin-math methodology (which is way better than a WAG), run a crude room-by-room I=B=R type load calc for each room based on the "after" picture of any insulation & window upgrades. This can be done using a spreadsheet tool like Excel or similar. The basic formula by exterior surface type is:

U-factor x square feet x temperature difference = BTU/hr.

For a 2x4 wall with R13 cellulose the U-factor is about U0.10 (give or take a bit depending on siding type). A wood sashed single pane with a clear glass storm is about U0.50, so does a solid wood 2"thick exterior door. We'd need a better description of the attic/ceiling insulation & construction to concoct a crude but reasonable U-factor for the ceiling losses. If the crawl space is unvented we can more or less ignore the floor losses.

The 99th percentile temperature bin in your area is about +15F, so with a 70F interior design temp you're looking at a 65F temperature difference.

So a 12 x 15' corner room with 9' ceilings would have 245', if it has three 10' windows that's 215' and the wall losses are:

U0.10 x 215' x 65F= 1398 BTU/hr

Assuming clear-glass storms over single pane wood sash the window losses would be:

U0.5 x 30' x 65F= 975BTU/hr.

If there's decent attic insulation (TBD) that number will be quite a bit lower than the other two and just adding those numbers together should be a close enough estimate for tweaking the radiation balance. For now we'll ignore the floor & infiltration losses.

If you then calculate the ratio of load to baseboard or other radiation ratings, it can be adjusted for reasonable room to room balance, with maybe 25% more radiation on the coolest-water end of the loop than on the warmest water end. (If you're running a modulating condensing boiler with a big loop delta-T it may have to go higher than that.)
 
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