|
| Author |
Message |
travellerw
Member
|
# Posted: 27 Aug 2026 02:13pm
Reply
Ok, this isn't cabin related but I thought I would throw it out here. I have a fairly complex HVAC question and wondering if there are any HVAC people here. The question involves hydronic and forced air combined heating (something we are undertaking in our big house).
|
|
spencerin
Member
|
# Posted: 29 Aug 2026 11:04pm
Reply
So what's the question?
|
|
travellerw
Member
|
# Posted: 4 Sep 2026 07:52pm
Reply
You asked for it! Its a long one.
Ok bear with me as I think this is going long (with a complex solution).
The house we bought (1.5 years ago) is equipped with forced air, however it has in-floor plumbing for the basement and main floor (no pipes on the second floor). The wife has asked to hook up the in-floor heating as the floors were VERY cold last winter (nasty Edmonton winter ). I have done a ton of research and I think I'm on the right track, but want some other opinions.
I have settled on a Rinnai IP090160C for both DHW and CH. Of course the big issue is the second floor that is only heated with forced air. If I use the hydronic heat as primary heat, then the second floor will never get heat (or rarely). My initial thoughts were to just leave the furnace fan on all the time, circulating the warm air around the whole house. However, I don't like how wasteful that is. So now I'm thinking of putting a thermostat on the second floor and using the air handler function on the Rinnai to turn the furnace fan on when the temperature up there drops.
I will then use 2 other thermostats in the basement and main floor with floor sensors as primary heat (the Rinnai supports 4 zones and 4 pumps). The original forced air thermostat will be set for 2C below that temp so the forced air only comes on when the hydronic can't keep up (its not uncommon for the temperature to drop 25C in one night here). An outdoor temperature sensor will be installed to disable the boiler when the temperature is above +10C. (The fan in the furnace will be controlled by both the original thermostat and the Rinnai air handler function)
AC will be controlled by the original forced air thermostat in the summer. (This should allow me to set that thermostat to dual mode and not have to change anything between summer and winter! Everything should be automatic).
Does this all make sense? or is it crazy complicated and I'm nuts? Is there an easier way to do it?
|
|
MtnDon
Member
|
# Posted: 4 Sep 2026 08:49pm - Edited by: MtnDon
Reply
travellerw, you are correct. That is a complex situation, and I believe the answer requires an experienced HVAC technician/engineer. The too-darn-cold-for-me winter comllicates things.
|
|
Brettny
Member
|
# Posted: 5 Sep 2026 08:46am
Reply
I believe you will need a thermostat and way to shut off the hot water and air to each system. How was this system setup before?
It may be easier to setup a condensing boiler and have the hydronic system setup independently.
If you want/need AC too it may be cheaper to install a mini split. Yes there not very efficient at 0F but the amount of weeks spent at those temps is prety low vs the rest of the saving throughout the year.
|
|
travellerw
Member
|
# Posted: 5 Sep 2026 01:51pm - Edited by: travellerw
Reply
To be clear, I left a bunch of details out as its the air handler function of the furnace I'm interested in. The rest of the design is pretty solid. Dual zone pumps using the controller in the boiler. Its just that second floor that makes things more challenging.
To be clear the house already has forced air heat and AC on all floors. With the hydronic hooked up, that would become secondary heat.
I think I might just build it find out! Like I said, I could always just leave the furnace fan on to circulate hot air on that second floor (every room has an air return).
|
|
Peewee86
Member
|
# Posted: 10 Sep 2026 02:36pm
Reply
Our main home is a rambler and like yours, was set up with the radiant pex pipe and insulation in the concrete flooring on the lower level. I’ve never set the system up because I’ve never had the extra money to buy the pump, valves and mini boiler. I’m told $8-10K to get my system up and running.
Like you, I also have forced air HVAC system that currently heats and cools the entire house. We close off most of the vents on the lower level during the summer months and in the winter we do the reverse. We open up all of the lower level vents and close off many of the upper floor vents. Even doing this there is generally a 5-7° temperature variation between the upper level and the lower level if I don’t run the HVAC fan.
In searching for a solution to running the fan constantly, I was able to find a thermostat that had programmable fan settings. There is a 20 minutes on and 40 minutes off setting in addition to the Auto setting and the continuous ON setting. We run the fan continuously at night while we are sleeping but then use the 20/40 cycle for the each of the other 3 HVAC daily cycles. On average, the fan probably runs about 50% of the time so I’m saving half of the electricity and half of the wear and tear that I would versus running the fan continuously. Also our HVAC unit uses a DC fan motor, which is quite a bit more efficient than the older AC fan motors.
Not an answer to your main question, but I hope this helps.
|
|
gcrank1
Moderator
|
# Posted: 11 Sep 2026 09:18am
Reply
I like that!
|
|
|
travellerw
Member
|
# Posted: 11 Sep 2026 08:41pm
Reply
Quoting: Peewee86 Our main home is a rambler and like yours, was set up with the radiant pex pipe and insulation in the concrete flooring on the lower level. I’ve never set the system up because I’ve never had the extra money to buy the pump, valves and mini boiler. I’m told $8-10K to get my system up and running.
If you are handy, you could put a system together for about $3500 as a DIY (cheaper if you only want the in-floor heating and not to replace your domestic hot water). Its really not rocket science and there is a lot of forgiveness in a hydronic heating system.
As to your suggestion. Its probably the best answer. I have an Ecobee that is capable of fully programmable control of the fan. I did actually think about that, but I have a bit of OCD (perfectionism) that probably blinded me. Now that you have brought it back to my attention, that is most likely the path I will go.
|
|
|
