radiant garage floor heat nad interconnecting boilers

Hammer

I have a 16 year old, 2,700 sq ft home in central PA with a 5-zone baseboard hot water heating system served by an oil-fired, cast iron, sectional boiler. I recently constructed a 1,200 sq ft detached garage approximately 60 ft from the house. I have not poured the concrete floor in the new garage yet, but I plan to install a radiant heat slab and interconnect to the house boiler system. My calculations show that the existing boiler should handle the extra load provided that I don’t keep the garage too warm in the dead of winter.

I could simply interconnect supply/return lines with the existing boiler and route them between the garage and the house, and then use an injection loop or secondary loop in the garage to serve the radiant floor. However, because of the price of fuel oil, I would like to install a wood/coal boiler (I have ready access to fuel) in the garage and “backfeed” the house (as well as heat the garage). I want to interconnect the two heating sources so that I can also use the house (oil) system to heat the house and garage during the fall/spring “shoulder” months and when I am out of town, but use the wood/coal system for the heart of the winter.

I have a number of questions that I am seeking answers to and hope that the experts out there can help. First, since I am interconnecting to a cast iron boiler with steel headers, I assume that the garage tubing should have an oxygen barrier. Is PEX-AL-PEX the best (or only) choice? If I further isolate the garage radiant floor via a heat exchanger and use glycol in the loop, do I still need the oxygen barrier tubing? Some people have told me that it is best to use glycol in a garage floor system in case of freeze-ups.

That was the easy issue. I’m mostly concerned as to the best method to interconnect the two heating systems and how they should be controlled. I’m looking for a good schematic that can help me out. Anyone know where I can find one? I’ve found some installation manuals from outdoor boiler manufacturers where they interconnect and piggyback onto an existing house boiler system. The schematics I’ve seen show the outdoor boiler connecting direct to the indoor boiler at the indoor boiler return connection. I suppose this makes some sense for a situation where the outdoor boiler may not putting out sufficient heat, then indoor boiler would make up the delta T. However, I wonder about the “reverse heat transfer” or standby losses by running 190F~200F water thru an “idle” boiler.

Ideally, in a new house installation, I would have a separate primary pump for the house boiler and all zones would use secondary loops. But, I don’t have that situation; all the house zones are piped direct to/from the existing boiler supply/return headers. I really don’t want to re-pipe my entire boiler room unless I have to. Is there a good way to interconnect? Should I install some type of automatic on/off valve on the inlet to the existing boiler? At 2”, that would be expensive, so in the long run, it might be less costly to re-pipe the existing boiler and house zones to a primary/secondary arrangement.

My last issue is how to best control the whole mess without spending a fortune. I assume that the underground piping (which is actually another question) between the house and the garage will act as a very long header that can be fed from either end. However, flow requirements thru the header will be different depending on which boiler is on line. In the “wood heat mode” (from the garage), there would be maximum design flow thru the header back to the house. However, in the “oil heat mode” (from the house), the flow requirement thru the header will be minimal (to serve only the garage). Compounding the situation is that the oil boiler will put out 190F~200F water to the garage, and since there is a radiant system with a lower supply water temperature required, the flow thru the header is reduced even further. Do I need a variable speed pump or just a bypass at the end of the loop? How should all of this be controlled?

Sorry for the excessive length. Thanks for any help and advice.

Hammer

radiant garage floor heat and interconnecting boilers

I have a 16 year old, 2,700 sq ft home in central PA with a 5-zone baseboard hot water heating system served by an oil-fired, cast iron, sectional boiler. I recently constructed a 1,200 sq ft detached garage approximately 60 ft from the house. I have not poured the concrete floor in the new garage yet, but I plan to install a radiant heat slab and interconnect to the house boiler system. My calculations show that the existing boiler should handle the extra load provided that I don’t keep the garage too warm in the dead of winter.

I could simply interconnect supply/return lines with the existing boiler and route them between the garage and the house, and then use an injection loop or secondary loop in the garage to serve the radiant floor. However, because of the price of fuel oil, I would like to install a wood/coal boiler (I have ready access to fuel) in the garage and “backfeed” the house (as well as heat the garage). I want to interconnect the two heating sources so that I can also use the house (oil) system to heat the house and garage during the fall/spring “shoulder” months and when I am out of town, but use the wood/coal system for the heart of the winter.

I have a number of questions that I am seeking answers to and hope that the experts out there can help. First, since I am interconnecting to a cast iron boiler with steel headers, I assume that the garage tubing should have an oxygen barrier. Is PEX-AL-PEX the best (or only) choice? If I further isolate the garage radiant floor via a heat exchanger and use glycol in the loop, do I still need the oxygen barrier tubing? Some people have told me that it is best to use glycol in a garage floor system in case of freeze-ups.

That was the easy issue. I’m mostly concerned as to the best method to interconnect the two heating systems and how they should be controlled. I’m looking for a good schematic that can help me out. Anyone know where I can find one? I’ve found some installation manuals from outdoor boiler manufacturers where they interconnect and piggyback onto an existing house boiler system. The schematics I’ve seen show the outdoor boiler connecting direct to the indoor boiler at the indoor boiler return connection. I suppose this makes some sense for a situation where the outdoor boiler may not putting out sufficient heat, then indoor boiler would make up the delta T. However, I wonder about the “reverse heat transfer” or standby losses by running 190F~200F water thru an “idle” boiler.

Ideally, in a new house installation, I would have a separate primary pump for the house boiler and all zones would use secondary loops. But, I don’t have that situation; all the house zones are piped direct to/from the existing boiler supply/return headers. I really don’t want to re-pipe my entire boiler room unless I have to. Is there a good way to interconnect? Should I install some type of automatic on/off valve on the inlet to the existing boiler? At 2”, that would be expensive, so in the long run, it might be less costly to re-pipe the existing boiler and house zones to a primary/secondary arrangement.

My last issue is how to best control the whole mess without spending a fortune. I assume that the underground piping (which is actually another question) between the house and the garage will act as a very long header that can be fed from either end. However, flow requirements thru the header will be different depending on which boiler is on line. In the “wood heat mode” (from the garage), there would be maximum design flow thru the header back to the house. However, in the “oil heat mode” (from the house), the flow requirement thru the header will be minimal (to serve only the garage). Compounding the situation is that the oil boiler will put out 190F~200F water to the garage, and since there is a radiant system with a lower supply water temperature required, the flow thru the header is reduced even further. Do I need a variable speed pump or just a bypass at the end of the loop? How should all of this be controlled?

Sorry for the excessive length. Thanks for any help and advice.

Weezbo

You came upon the right place to ask those ?'s

it also is important to get someone to do the work for you that has knowledge of these things. Look under find a Pro. maybe there is someone in your area....

Unknown

in ur thread...

In ur entire thread, u have asked many right questions regarding the mechical aspects of ur system, Weezbo's right, find a hydronic heating pros while we can help you. In meantime, what you can do is to insulations the heck in ur earthly area, concrete, etc more u covered the better off u are... I've seen systems without insulations, bigger bolier runs all all the time while same size building with insulations using smaller boiler ran less frequnly(sp)....

hr

You will need to repipe

somewhat in the boiler room. I would build a primary loop and treat the boilers and various loads as secondaries.

For the garage boiler and system you would want to glycol the boiler and tube. For this a plate heat exchanger at the primary loop inside your home would be my approch.

Plenty of dual pipe underground pex tube available theses days. Uponor, Heatlink, and most all of the OWF companies offer this pre insulated tube assembly.

I like the InsulSeal product, www.insulseal.com,an insulated PVC condiut that you install whatever tube you like inside.

A tekmar two stage boiler control could watch and operate the two boilers automatically. or it could be built with some diffefential controls.

A mini tube injection would be ideal for the garage if both boilers could be located in the home. This would allow two 1/2 or even 3/8" lines to be run to the shop and mix for the slab in the shop.

Grab some paper and start drawing away. Dans books available in Books and More will show various P/S piping options. Plenty of good info and drawings in Siggys articles at PMmag.com.

I know tekmar has control wiring drawings for these systems also, contact a tekmar rep or dealer, or try their website. this is a common and do-able system.

hot rod

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