Radiator Heating Issues: Pex/with oxy barrier

[Soopergal]

We are in the process of renovating our house. Our house is approx. 100 years old. We hired a general contractor to do all the work including the heating system. Our heating system currently only have old radiators on the main floor and the upper floor. We've asked our contractor to install new rads in the basement and create 2 zones, one for upstairs and another one basement replacing existing rusty pipes.

It seems that the HVAC subcontractor is using a combination of Pex and pex oxy barrier pipes to replace the old pipes. After reading comments on the internet regarding Pex vs Pex al pex vs Pex al pex, I'm wondering if we are working our way in to a bad situation. My main concerns is that these pipes are connecting to the old rads. Would the pipes start to corrode easily because we are not using Pex al Pex or pex with oxy barrier though out? Should they not be using Pex al pex everywhere or pex with oxy everywhere not just in some parts?

Here's the oxy barrier spec.
http://www.cbsupplies.ca/products/cross-linked-polyethylene-pex-pipe/canpex-oxy-barrier-pipe/

My other concern is that pipes get really hot and start making loud noises. We are planning to have a tenant in the basement.

Any thoughts please?

 

[Dana]

Any type of oxygen barrier PEX is good enough. PEX without oxygen barriers will not only corrode the radiators (which can go a long time), it'll eat away at iron-impeller pumps.

PEX expands/contracts quite a bit with temperature and usually has to be installed where it doesn't have much friction against framing/flooring etc or you'll hear it. It's usually suspended with plastic clips, and allowed to flex. It should never really be loud though, not like the ticking & whining of metal pipes on wood framing.

Most heating systems are set to WAY higher temperatures than is needed to heat the house. If you're replacing the boiler with a condensing boiler it would normally come with "outdoor reset control", which has to be programmed and tweaked (better for the informed DIYer than calling the contractor back 10x to tweak it up or down a few degrees), but once it's dialed in the water temps will never be higher than the radiation needs to cover the load, and the room temps will not vary much- it'll be steady & comfortable all the time.

If it's a cast iron boiler it probably doesn't have outdoor reset control, and there are limits as to how low the water temp can be without damaging the boiler. Most cast iron boilers out there are oversized for their actual heating loads by more than 2x , as are the radiators. But there are retrofit economizers and outdoor reset controls that can work with old cast iron too. The original heating system in an 100 year old house was for an air-leaky uninsulated house with single pane windows, not the house that you'll have post-renovation.

It's a good idea to keep a running heat load calculation spread sheet on a room-by-room basis, as well as how much radiator is serving each room. You want to keep the load/radiation level within a reasonable range on any one zone, and ideally at a ratio where it doesn't need more than 140F water to heat the place even at your 99% outside design temperature.

This is a bit outside the range of what a general contractor is good at, and many HVAC contractors don't bother (but they SHOULD). It's not rocket science either. YOU can do it, and the better you understand it, the more likely it is that you'll have a satisfactory result in the end, and you can sanity-check what they're doing (and it sounds like the HVAC folks may need some sanity checking if they're using PEX witout oxygen barriers.) It all starts with the room-by-room load calculations, using either Manual-J methods (more complicated, but more precise) or an I=B=R approach (similar, but easier, can run it using standard computer spreadsheets like Excel, etc.)

Hopefully you are insulating that basement as part of the finishing project, and doing something other than just slapping up a 2x4 wall with batts(?). There are a lot of ways to screw up finishing a basement, not all GCs are great at figuring that out either.

 

[Sponsor]

 

[Soopergal]

Thanks Dana. Appreciate your input. We have a Viessmann boiler. Yes, we will be insulating the basement. I've raised my concerns with the GC. He's disputing our points. He's saying his system will work and if we want to address our concerns we have to pay extra to change the pipes etc. Argh! Don't know what to do now.

 

[Dana]

The methods by which the basement gets insulated matter (a lot) in terms of mold risk. IRC 2012 code min for US climate zone 4 is R10 continuous insulation or R13 between studs, but for an R13 studwall approach to be mold-safe you need a layer of R3.75 minimum between the studs & batts, with a vapor retardency of 3 perms or less, and NO interior side vapor barrier. Without the foam there will be wintertime moisture accumulation in the above-grade section of the wall, and without the lower vapor retardency ground moisture wicking up the foundation from the footing can get into the studwall faster than it can leave.

R10 in the form of 1.5-2" foil-faced polyisocyanurate (seams taped with foil tape) or 2.5" of EPS (with or without facers ) held in place with 1x furring through screwed to the foundation works, with the finish wallboard nailed to the furring. 1x4 furring works better than 1x3, since it has less twist and is less likely to split.) If polyiso, keep the bottom edge off the slab to prevent moisture wicking into the foam. That's not an issue with EPS.

It's also worth putting at least R4 foam under the bottom plate of the studwall to keep warm enough to avoid moisture wicking up from the slab into the wood, &/or summertime moisture accumulation at the bottom of the stud plate, since the subsoil temps are lower than the average outdoor dew point temp. Extending R4 (or more) under any wooden subflooring for a finish floor would be enough to keep mold from growing in the subfloor or under rugs. Rugs on uninsulated slabs may take the chill off your feet, but creates a mold risk.

Viessman boilers come in a huge range of sizes and output. The min-fire output needs to be low enough to not short-cycle the boiler when serving the zone with the smallest amount of radiation at condensing temps, or it becomes abusive of the boiler, increasing maintenance, losing efficiency, and shortening it's lifespan. With sufficient thermal mass from high-volume radiators oversizing & short cycling is much less of an issue, but since the basement's load is probably very small, it's better if the radiation is sized for the min-fire output of the boiler rather than for the basement's very low load.

 

[Soopergal]

Thanks Dana. I'm still pressing the contractor to make the changes without additional charges. Do I have to look into the municipal code or is there somewhere else I should go to back up our findings? Here are our main issues we are disputing with the contractor.

1. Corrosion of Radiators and Pumps
2. Noise Concerns – PEX is installed too close to the framing.
3. Some of the Pex pipes running up outside walls
4. Incorrect Viessmann installation

 

[Dana]

SFAIK It doesn't violate building codes to use PEX without oxygen barriers in heating systems. But it may void warranties for boilers or pumps. Corrosion would take forever to actually damage radiators. It's really the pumps & boilers that need to be protected. Boilers with stainless steel heat exchangers (like all new Viessmanns, I think) will have less of a problem with it than those with aluminum or some other materials in the heat exchangers. But iron-impeller pumps can be a problem.

The amount of non-barrier pex matters- if it's just 15' it's not worth going after, but if it's 1500' it is a serious issue. (see: http://www.mrpexsystems.com/pdf/diffusion.pdf ) But an HVAC contractor who uses ANY non-barrier PEX in heating systems has a professional credibility problem.

It doesn't violate code to install heating system plumbing in such a way that the expansion/contraction creates noise issues.

It may be worth vetting the boiler installation through the Viessmann distributor, or a contractor recommended by the distributor.

BTW: The minimum amount of foam required for dew point control on the basement walls in my previous post was mis-stated. R2.5 would be enough for a 2x4/R13 studwall, but the lower vapor retardency is still necessary. (Half inch R3 polyiso would get you there.) I'm sure there are existent proofs of houses that have no exterior side foam or exterior side vapor retarders in basement studwalls that have no mold issues, but there are also many that fail. Fiber insulation should never be in direct contact with concrete due to moisture wicking forces, but all fiber insulation needs air-barriers tight to the fiber on both sides to perform at their rated R values.

 

[Soopergal]

Thank you so much Dana. You are superstar. It seems I have to build case to resolve this with the contractor. So really appreciate you sending the links etc.

 

[Soopergal]

Sorry, one more question - we've noticed one of the pex pipes is running up the outside wall. Wouldn't this cause them to freeze?

 

[Reach4]

Sorry, one more question - we've noticed one of the pex pipes is running up the outside wall. Wouldn't this cause them to freeze?

Do you mean on the inside of an outside wall, or the outside? Is it a heated space?

 

[Dana]

As long as the pipe has the bulk of the wall insulation on the exterior side it won't freeze. If the wall cavity is uninsulated there is a risk of freeze up if the system isn't running during a cold snap (say, during a lengthy power failure when it's 10F or colder outside during a Polar Vortex event.)

Jersey City's typical mid-winter mean temperature average is about +30F, and overnight excursions into the 20s aren't too risky, but we all know that it can get much colder during atypical winter weather events.

 

[Soopergal]

Sorry about the confusion I'm in Toronto. Let me update my profile. We tend to have ice storms frequently and have gone through lengthy (5 days) blackouts in the past. So my concern is that pipes may freeze with the current configuration.

 

[Soopergal]

Reach, inside of an outside wall.

 

[Soopergal]

Also, we got a quote from another guy to finish off the heating. He said he's going to use PERT instead of PEX. Is PERT going to solve the problems I mentioned above? I'm getting even more confused.

 

[Dana]

PERT tubing designed for heating systems always has an oxygen barrier. It's only been around a couple decades, used mostly in Europe, but it has a good track record.

Toronto is just a BIT cooler during Polar Vortex events than Jersey City, eh?

But as long as there is more insulation to the exterior of the pipe than there is between the pipe and the interior you'll do just fine from a freeze risk point of view. If you were in Winnipeg it could be a potential freeze up issue, but not Toronto. Five days of -15C or colder weather without power would be a problem (even if the pipe were completely inside, and not in an exterior wall), but Toronto's mid-winter average daily temps are much warmer than that.

 

[Soopergal]

It's pretty much Polar Vortex all winter.

 

[Magneto]

PEX can expand and retract if it freezes up so i would still go with the PEX. PEX-AL-PEX would be your best option due to its ability to maintain higher output of pressure. It can also withstand heat up to 200 degrees Fahrenheit so you dont have much to worry about. Im a big fan of PEX personally. ITs obviously becoming a hot commodity on the plumbing and heating industry for a reason.