I am planning a 2100 ft^2 walkout bungalow. I will be installing radiant in-floor (hydronic) heating in the basement level but due to costs I may do a high velocity fan coil/ductwork system for the main floor. Question about ventilation... I can connect an HRV to the furnace duct but if I run some duct to the basement for ventilation I will have 2 sources of heat to the basement. I don't want this as one system will compete with the other. Should I bypass the fan coil for the basement ventilation duct and ensure balancing dampers are installed ? What have others done?

Where are you located?

I would recommend having a dedicated duct system for the HRV or use HRVs that don’t require any ductwork (e.g., Lunos, Ventacity, etc). Here's some info on the HRV duct options:

GBT Forum HRV Duct Option Discussion

I would recommend a mini split in lieu of a furnace and high velocity system, especially if you will require AC. Mini splits and HR floor heating work well together.

As long as you zone your heating areas properly, you won’t have any issues.

I'm in Calgary Alberta and will not be installing AC. Thanks very much for the reply...much appreciated. I do like the idea of dedicated duct for the HRV

...also, Here in Alberta, electricity is expensive and natural gas is very cheap. This makes heat pumps much less cost effective.

In that case I would recommend doing HR floor heating on both levels and using an efficient mod con gas boiler as the heat source. Be sure to accomplish a good heat loss analysis (e.g., ACCA Manual J, ASHRAE or equivalent) so as to properly size the heat source. You might also want to consider using a whole house fan to allow cooling the building in the cool Summer evenings by just opening some windows and running it for a couple hours.

Thanks, In your opinion should I go with a lightweight aggregate to cover the main floor radiant tubing or would you go with the "Warmboard" product or equivalent?

Both the Warmboard and gypcrete (or equivalent) thin slab (usually 1.5 inch thick) HR emitters perform nearly equally well in terms of heat transfer efficiency. A normal 4-5 inch thick concrete slab HR emitter performs a little better. The above-floor plate systems don’t perform nearly as well and the below-floor plate systems should be totally avoided unless your really really want HR floor heating and you are willing to accept very poor performance. HR emitter performance is all about maximizing heat transfer from the PEX tube (i.e., maximizing conductivity from the exterior surface of PEX to the emitter substrate and floor surface) and keeping the ratio of R-value above the PEX to that below the PEX as small as is economically feasible. So between a thin slab and the Warmboard, it really comes down installed cost and local installer competency. John Sigenthaler’s Modern Hydronic Heating is the best reference book on all things HR. We also have free DIY heat loss analysis and HR floor heating design software on website if you so inclined too.

Great info...thanks again .

I am planning a two story with a multi-zone mini-split AC but downstairs is a garage/shop that is well sealed from the upstairs.

My plan is to do two HRVs, one upstairs and one downstairs to ventilate them independently and allow for different thermostat settings.

It seemed easiest to go that way for me. It might make sense for you too but your situation is different.

HRVs don’t use thermostats and since they operate at a relatively high efficiency and at a relatively low flow rate, they don’t significantly affect interior temp either.

Dedicated duct HRVs perform the best. Put the stale air inlet registers in bathrooms and laundry rooms. Put the fresh air outlet registers in bedrooms and living spaces. Put switches in the bathrooms to allow running the HRV at maximum flow rate for some duration as needed.

I would think one HRV for the entire building would be best. Just be sure to size it properly and there is much info on the GBT forum about this subject.

I know, but if I want to condition my upstairs to 74 degrees and my downstairs to 84, the zones can be completely independent if the doorway is sealed and the ventilation is independent.

Not sure why you would want to condition living space to different temps? I can see conditioning one area to 74F and NOT conditioning some other area at all, or NOT conditioning it for some period of time and then conditioning it to 74F when desired. Anyhow, good luck with your project!

If it's 120 degrees outside, I don't think I want to leave my garage shop unconditioned even if I'm not using it.

I'll have to see how it works out. I will have two garage doors that probably won't seal perfectly but I'm going to tape the subfloor of the second story and blow in insulation between the floor joists for sound insulation to separate the zones and use an exterior style door between the shop and living area. This should allow me to do a small amount of shop conditioning so that I can run in to pick something up without breaking a sweat and also satisfy the firewall and air sealing requirements for attached garage construction.

Hopefully I'll find that the conditioning cost is not high and I'll be able to keep both at a similar temperature with the amount of solar I have planned but if that doesn't work, they will be zoned and as close to air sealed as I can get.

We don’t condition our garage and shop, and it doesn’t get above 72F even when we have a couple weeks of triple digit temps. Your location may be hotter and not as diurnal as our location. But if your location is low humidity diurnal and swings about your desired interior conditioned temp (or about your acceptable interior unconditioned temp), just know that there an insulation and thermal mass design solution that would negate needing any significant HVAC solution. And once you reduce your HVAC needs to the lowest level without exceeding insulation diminishing returns, then you can finish the design with lowest possible cost HVAC and photovoltaic systems. However, if you simply need to increase the size and expense of your photovoltaic system to address your shop power needs, that’s an entirely different design motivation.

At my build site it can go for weeks without dropping below 90. The only upside is that the solar heat gain will be minimal because my living area will be on top of the shop.

I am also going to be doing things in the shop that generate heat occasionally and I'm going to keep things like my computer in the garage to keep the noise and constant 30 watt heat in the less conditioned space.

It would be great if I only use the AC when I'm using the shop but I have a feeling that the cost to keep it in the 80s during the summer when I'm not using it won't be too bad. If I wind up net positive by a lot, I might keep it at the same temp as my living space but we will see.

In that case it makes perfect sense to design the insulation to the diminishing return level and achieve net zero/positive as you are proposing. Just take the time to accurately find that diminishing return level...and be sure to provide adequate insulation (and space to put it) between your separate zones...