Home>Discussions>INSULATION & HVAC>Can I install Pex tubing in a wall?
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CindySHess
Can I install Pex tubing in a wall?

I'm restoring a small powder room that had an old cast iron radiator. The radiator takes up valuable space and am wondering if I can put pex tubing in the wall for heat. The floor is concrete, so that's out. I'm currently installing radiant hot water heat in the adjacent hallway and kitchen using the "warmboard" system, so I'll have leftover pex tubing and a place to hook up. The walls are gutted down to the brick (no insulation). I'm thinking of wrapping walls and ceiling with reflective insulation, running tubing between studs and then installing my drywall and beadboard. I know that heat rises, so that's a negative, but it seems like a cost effective solution since I could add it to end of an existing zone. What are your thoughts?

NashuaTech
Re: Can I install Pex tubing in a wall?

Cindy:

Yes, installing PEX in walls for radiant heat is done quite often in commercial applicaitons where, as in your case, access to floor radiant is not avaialble---Google "radiant wall heating" for more info.

Be aware also that there are several other options available such as one or two kickspace heaters--these have a very small footprint of 12" X 16" X 4" & fit under a vanity cabinet, connect to the hot water piping & have a small fan & temp control---if you buy a kickspace buy one that has a QUIET FAN.

An overhead exhaust fan/heating lamp is often installed near the tub/shower to provide spot warming.

Both the above items are quick to install & have t-stat temp control---the PEX in the wall actually acts as a large radiator (not hot to the touch, more subtle) that warms the entire wall area & the heat "radiates" for hours---so the heat doesn't actually rise--it sends invisible heat waves out that give up their heat when they hit a solid object, like people, or an adjacent or opposite wall.

You would have less t-stat control over the wall PEX temperature-wise (unless you have a manifold setup for all the PEX heat lines at the boiler) & the heat level would depend on at what point you tie the PEX into the boiler main supply line---if the tie-in is at the "end of the line" of the pumped hot water supply you would be dealing with 140 degree water instead of 180 degree water.

If you have a large bathroom, it may be best to put the bathroom on a separate t-stat-controlled zone using a zone valve at the boiler--again, this would not be necessary if you have all your PEX heat lines coming out of a manifold at the supply output.

Hydronic towel warmers (also tied into the hot water heat piping) have become very popular in recent years & double as an out-of-the way thin metal stainless steel radiator---Google "hydronic towel warmer" (with & without the quotes) to get some online samples--these items tend to be very pricey.

Your first step is to do the math as to how many heat btu/hour the bathroom needs on cold winter days to keep it warm & comfortable, especially after a shower or bathing.

Do a HEAT LOSS CALCULATION to determine how many btu's/hour are exiting the bathroom---a common rudimentary HLC is to use a heat loss factor of 80: thus a bathroom that measures 10' X 10' = 100 sq.ft. X 80 = 8,000 btu/hr as its heat loss---a single kickspace heater rated at this level would cost well under $100---the Myson site below is just one example---scores of companies make kickspacers---Google "hydronic kickspace heaters".

The PEX heating output in the wall is usually calculated at 23 btu/sq.ft.---thus a PEX heated wall area of 5' X 20' = 100 sq.ft. X 23 = 2300 btu/hr.---the PEX in this case would provide only 25% of the heat needed---take the measurements of your bathroom & the available area that PEX can be installed--the ceiling can also be included---these numbers are rudimentary, obviously if you pack more PEX closer together inside the walls you'll get more heat output.

The Slant/fin free HLC is currently not online (send them an e-mail & ask them why not), but it is free & an excellent one---try to find a free online comprehensive HLC for this work--the "house needs" site has a lot of prqctical info---I have no relationhip with any of the sites below, they are listed only for informational purposes.

http://www.slantfin.com/heat-loss-software.html
http://www.houseneeds.com/shop/atop/radiantheatingindex.asp
http://www.bgmsupply.com/calculateheatloss.asp
http://www.beacon-morris.com
http://www.hearth.com/calc/roomcalc.html
http://www.hydronicalternatives.com

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