Radiant & potable Same heater

Unknown

I"mnot sure I understand what you are doing.

one joist bay has two runs of 5/8" pex, then you skip a bay, then another bay has two runs of 5/8"??

That's not a very good install. You don't need 5/8" for that and you'll have crazy heat stripes.

You need a heat exchanger as well. I'd use a variable speed injection controller for the water heater side pump.

Loops need balancing valves on them.

Hope that helps.

adayton_2

BTU and control circuit layuout

Looking for assistance in control device and circuit layout.

Subject:

1. existing 1/2 inch pex in 20 X 20 foot room.

2> adding TWO 20 X 20 rooms with double 5/8 inch pex

strung every other beam (bay).

3> New water heater 75,000 BTU A.O. Smith GAS fired Vertex

*** http://www.hotwater.com/products/residential/rg-vertex.html ***

has standard 3/4 inch potable out top and out of side for radiant heat.

4. Geographic locale: Long Island, N.Y.

Unit will provide house potable and three room radiant heat.

Concerned about overall BTU capacity and pump types

necessary to drive the two different pex diameters???

Also what would be preferred mixer/control devices?

Any ideas?

Dan C._4

Does the water heater have a seperate coil in it for space heating?

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adayton_2

No seperate coil

just two sets of supply/return 3/4 inch feed lines.

try this link. The model number:GPHE50100

http://www.hotwater.com/products/residential/rg-vertex.html


Manual:

http://www.hotwater.com/lit/im/media/res_gas/197423-001.pdf

jp_2

code?

does your local building code allow for combined space heating and domestic hot water?

adayton_2

potable code

probably allows as long as pex and EVERYTHING in the circuit is rated potable, however I believe the pex is NOT so will probably opt for seperate tankless on-demand. Alternate would be to use a heat exchanger for the potable section. any pros or cons to either??

jp_2

heat load

what is the expected heat load for the 1,200 sq ft ?

Unknown

If the vertex will be there anyway, and has the output to meet DHW and heating, use the heat exchanger, it will do a better job for heating than the tankless.

adayton_2

NRT.Rob, crazy heat

stripes for sure LOL :-)..

My oops in description, every other END joist in each bay was double drilled (1 1/4") to accept dual 5/8" pex running in each bay.

What brand/model variable speed
controller and balancing valves would you advise?
""Author: NRT.Rob

I"mnot sure I understand what you are doing.

one joist bay has two runs of 5/8" pex, then you skip a bay, then another bay has two runs of 5/8"??

That's not a very good install. You don't need 5/8" for that and you'll have crazy heat stripes.

You need a heat exchanger as well. I'd use a variable speed injection controller for the water heater side pump.

Loops need balancing valves on them.

Hope that helps. ""

adayton_2

heat load

is actually THREE 200 square feet rooms, each with at least one exposed outside wall. all three are well insulated. Two will have newly installed 5/8" pex and one has pre-existing 1/2" pex.

Unknown

I'd just use 1/2" pipe two per bay, connected to a manifold with flow meters/balancing valves, and loop the rooms individually so I can balance/zone them.

I like a tekmar 356 injection mixing controller for this kind of a setup (two pumps and a heat exchanger). If you are willing to run "bang bang" and your water temps aren't too high, then you might skip it too, but it's a nice addition.

jp_2

how

did you attach the 5/8 pex to the floor?

Rich L.

Attachment

Are you using plates or just staple up?

singh

L.I

Why the 5/8" tube , 1/2" ok.


http://www2.iccsafe.org/states/new_york/NY_Mechanical/mech_frameset.htm

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adayton_2

Pex fastening

is by stapled up aluminum plates.

adayton_2

Why 5/8 inch PEX

Because the very old and very thick double floors in this very old building provide a deterrent to heat. The double
5/8 inch was thought to provide more "horsepower" (higher
flow/BTU throughput). Before you ask, NO!, the antique custom floors could not be disturbed in order to lay the radiant pex on the top side.
The layout is attached. Dual 5/8 pex running through EACH bay.

adayton_2

Tankless -vs- Vertex Condensing

The tankless was only for the domestic potable, since the whole system is not potable certified. Also if one unit fails you dont lose both functions (heat AND hot water)
Also, doesn't a heat exchanger cost almost as much as a small tankless?

adayton_2

Seperate coil

No

Manual:

http://www.hotwater.com/lit/im/media/res_gas/197423-001.pdf

Unknown

It does, but the vertex will do a better job of both heating and hot water, and if it's there, you should use it for both.

the "whole system" only has to be potable up to the heat exchanger.

Unknown

5/8 will not help your output and that's about the most difficult possible way to install a joist heating system ever.

3/8 or 1/2 pipe, all penetrations on one end, using the "pull method". down and back through the penetrations, then pull from that up the joist bays with a loop of tubing.