Nathaniel Hieter
New Member
Moderators: My apologies if I chose the wrong forum. I wasn't quite sure where this one fit.
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For the past fourteen years my radiant heat system, fired by oil heat, has served me well. Unfortunately, despite wonderfully low oil prices, I find myself under pressure to switch to propane.
Bear in mind that I am DIYer and NOT a professional.
Here is my current system that I designed and implemented many years ago:
Type: Under framed floor, stapled-up
Zones: 4
Loops per zone: 2/2/4/6 each 250-300ft
Tubing: 7/8in pex
Heat Transfer: continuous 8x12in aluminum plates molded around pex
Insulation: double foil bubble wrap 1in below pex, backed by R19 fiberglass
Pex Spacing: 3 zones have 8in spacing, 1 zone has 16in spacing
Floor: hardwood downstairs, carpet upstairs
Heat Source: Bock oil-fired water heater
Operating Temp: Aquastat set to 140.
Return Temp: Varies but usually less than 110.
Plumbing: 2in manifold, each zone has its own pump
Pressure: closed system, 12-15psi
Location: Hudson Valley NY, well insulated but lots and lots of glass
(Domestic hot water served by Steibel Eltron Accelera 300.)
Possible replacement options (that I can think of, feel free to offer others):
Option #1 seems pretty straight-forward, a project that I can tackle myself. There seem to be direct-vent options with decent efficiency. Since my previous tank corroded at ten years I’m a little gun-shy about tank systems. Price seems in the 3-4k range. Shelling out 4k every ten years would be irksome, but not impossible.
Option #2 is harder. I understand the principles of primary/secondary plumbing, the importance of spacing pump flow-rates etc, but….. realistically I will almost certainly need professional help. I have a good friend who is a competent plumber so this is not a deal-breaker. Price seems in the 5k+ range, but I would expect the system to last longer than 10yrs given reasonable upkeep.
Option #3 has attractive pricing, but would probably cause me the most grief to get it working efficiently. In this configuration I would keep the Bock water heater as a buffer tank. I would insert the primary loop after the outlet of the water heater, pushing into the pressure expansion tank. The aquastat on the water tank would be used to control the pump pushing into the tankless water heater. Power would only reach the aquastat if one of the zones called for heat. This would ensure a maximum temperature feeding the tankless unit. To enable a high set point for the output temperature I would have to ensure the flow rate through the tankless is less than the flow rate through an individual loop via sizing the tankless pump and/or a mixing valve. Temperature settings would require some experimentation. Perhaps 125 for the tank and 165 for tankless output. I would think that a 40 degree differential would be the minimum required for the tankless to work efficiently. The price point is ridiculously (suspiciously?) attractive even considering the need for a buffer tank. (Replacing a simple side-kick is cheaper than one designed to accept a oil/gas burner.) However…… There are so many things that could go wrong!
Questions:
Thanks in advance for any feedback!
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For the past fourteen years my radiant heat system, fired by oil heat, has served me well. Unfortunately, despite wonderfully low oil prices, I find myself under pressure to switch to propane.
Bear in mind that I am DIYer and NOT a professional.
Here is my current system that I designed and implemented many years ago:
Type: Under framed floor, stapled-up
Zones: 4
Loops per zone: 2/2/4/6 each 250-300ft
Tubing: 7/8in pex
Heat Transfer: continuous 8x12in aluminum plates molded around pex
Insulation: double foil bubble wrap 1in below pex, backed by R19 fiberglass
Pex Spacing: 3 zones have 8in spacing, 1 zone has 16in spacing
Floor: hardwood downstairs, carpet upstairs
Heat Source: Bock oil-fired water heater
Operating Temp: Aquastat set to 140.
Return Temp: Varies but usually less than 110.
Plumbing: 2in manifold, each zone has its own pump
Pressure: closed system, 12-15psi
Location: Hudson Valley NY, well insulated but lots and lots of glass
(Domestic hot water served by Steibel Eltron Accelera 300.)
Possible replacement options (that I can think of, feel free to offer others):
- Just swap out the oil-fired water heater for a gas-fired water heater.
- Condensing gas-fired boiler
- Tankless gas-fired water heater (such as Takagi TH3)
Option #1 seems pretty straight-forward, a project that I can tackle myself. There seem to be direct-vent options with decent efficiency. Since my previous tank corroded at ten years I’m a little gun-shy about tank systems. Price seems in the 3-4k range. Shelling out 4k every ten years would be irksome, but not impossible.
Option #2 is harder. I understand the principles of primary/secondary plumbing, the importance of spacing pump flow-rates etc, but….. realistically I will almost certainly need professional help. I have a good friend who is a competent plumber so this is not a deal-breaker. Price seems in the 5k+ range, but I would expect the system to last longer than 10yrs given reasonable upkeep.
Option #3 has attractive pricing, but would probably cause me the most grief to get it working efficiently. In this configuration I would keep the Bock water heater as a buffer tank. I would insert the primary loop after the outlet of the water heater, pushing into the pressure expansion tank. The aquastat on the water tank would be used to control the pump pushing into the tankless water heater. Power would only reach the aquastat if one of the zones called for heat. This would ensure a maximum temperature feeding the tankless unit. To enable a high set point for the output temperature I would have to ensure the flow rate through the tankless is less than the flow rate through an individual loop via sizing the tankless pump and/or a mixing valve. Temperature settings would require some experimentation. Perhaps 125 for the tank and 165 for tankless output. I would think that a 40 degree differential would be the minimum required for the tankless to work efficiently. The price point is ridiculously (suspiciously?) attractive even considering the need for a buffer tank. (Replacing a simple side-kick is cheaper than one designed to accept a oil/gas burner.) However…… There are so many things that could go wrong!
Questions:
- Are there pros/cons in each choice that I have overlooked?
- Is anybody on this forum actually having any success with option #3?
Thanks in advance for any feedback!