Room air exchange necessary with radiant heat?

Steve Eayrs

have little to do with the type of heat you have, but a lot to do with how tight your house is. Even a less-comfortable scorched air system, in a tight house needs some outside ventilation.

And yes they are needed in houses that are tight. Of course if you live in some areas, where most people don't build very tight, then you may come to the conclusion that they are a needless extra item.

If you lived in an area w/ R-60 ceiling, R-25 min. walls, window with high values, and vapor barriers where closing a door can be felt in your ears, they are needed.

You can argue all you want about it being overkill, but after hearing all the comments about massive fuel consumption, in the winters, and high AC in the summers, from many on this site, I would think there would be more concern for tighter construction on the East Coast.

Up here in Alaska there are many new 2000-2500 sq.ft. houses with $70-100 monthly average costs, for hydronic heat and a lot of dhw, and some less than that. It kind of speaks for itself. (and this is an area without NG!)

Without the HRV the windows would be dripping, and mold would be growing in the corners. My personal experience is good insulation and ventilation is very useful anywhere, regardless if your trying to keep the cold or the heat out.

O...yes....Unless an attic is part of the heated envelope of the house, it makes a lot more sense to install it in the mechanical room or somewhere in the house, where it will do a better job, and not drip condensate everywhere, as it would in a cold attic.

Steve

Annie Hall

Is it necessary to install a room-to-room air exchange system (ducts to each room, blower in the attic) in a home heated solely with radiant in-floor heat?

ed wallace

room to room air exchangers

no its not and why would you? inquiring minds whant to know

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Annie Hall

I know I need to go back to this contractor with a few questions. I'm not sure that what he was describing to me was a complete HRV system (I assume HRV is heat recovery ventilation?). He told me that the system consists of ducts connecting each room and a blower in the attic to move the air from one room to another. Nothing about introducing outside air, or recovering heat. This system would be separate from the whole house fan specified by our building codes to run periodically at 150 cfm and, I guess, ventilate the house (although I have not yet figured out where the outside air is coming from..still researching the codes.)

This contractor was telling me that the air exchange system is necessary only for radiant heated homes because otherwise there is not mechanical way that air moves from, say, bedrooms, to other living spaces and therefore might get stale. I find this odd, because half the year we don't run heating systems in this part of the country (the Pacific NW) and no one complains about stale air.

[Deleted User]

Tighter house

Maybe this contractor builds a better,(tighter)house, and that is why it is an issue. Believe me, tighter is always better. With HRV you have all the advantages of lower energy bills, fresh air, no mold, and a healthier house. Go for it! You might make sure he has the credentials to design and install..

Steve Eayrs

I agree

A tight house needs ventilation, but regardless of the type of heat system. If stale air is the problem, its not magically solved by hot water baseboards or forced air.
Steve

Mike T., Swampeast MO

Something wrong in that logic

"...telling me that the air exchange system is necessary only for radiant heated homes because otherwise there is not mechanical way that air moves from, say, bedrooms, to other living spaces and therefore might get stale..."

Not only because the heating system isn't being used much of the time but because, by that logic, ANY heating system that doesn't "mix" the air between spaces (i.e. anything BUT centralized forced air) would "require" this as well.

In CA at least (unless things have recently changed) the "incoming" air is often nothing more than a hole in an outside wall...

Annie Hall

A tight house needs ventilation, yes. My experience is very limited, but in the only other house I built we put in the insulation and efficient windows per code, and then put a snap-open vent in every room with an outside wall. A whole house fan with a timer was placed in the bathroom, and the idea was that the fan would kick on once or twice a day and pull some fresh air in through all of these little vents. I am assuming that some such thing is still required, although I've not seen similar vent holes in the newer construction that I've been in lately. ...Anyway, I'm just wondering why this guy is telling me that we need ducted air exchange between rooms, and whether that is overkill nor not. I certainly do want some outside air entering, but, as perviously posted, a hole in an outside wall would do that job nicely.

Steve Eayrs

Annie, There are number of exhaust only systems around here. That is what we call what you just described above. The outside vents used most around here are called fresh-80's, with either one central, or individual bath fans, that have timers attached.
These systems operate by creating a slight negative pressure on the whole house. May work in some houses, but can be a big problem w/ natural drafting appliances, or heating equipment, wood stoves etc.. You can actually pull exhaust fumes down the stack into the house. Most exhaust only systems I have seen have some of the outside air vents closed off, because they were not originally placed well, and created a cold draft.
You can't expect most atmospheric boiler to run good with such air systems. The HRV system is balanced and brings in the same cfm as it exhausts.

Now if I could just figure out how to get enough makeup air for those 1000-1500cfm range hoods, which are the same problem as above X 10!

Steve

Mike T., Swampeast MO

High-volume Range Hoods

Fine Homebuilding June/July 1995 has an article nearly completely devoted to this. Many strategies described culminating in a dedicated fan-forced inlet operating in concert with the hood and even using pre-heating in cold weather with the REALLY high-volume units!

Commercial ranges for people who rarely if ever cook and granite countertops in kitchens that will likely be ripped out in less than 15 years when fashion changes are just two of the reasons that HGTV is locked out of my television!

Other work takes me in quite a number of high-end homes--typically in the winter time around the holiday season. I'm still amazed at the number of corian (not my favorite either) but highly serviceable countertops being ripped out for granite and the number of truly commercial ranges being installed.

Almost inevitibably I see that they have been weatherstripping and sealing the hell out of the garage. Why? Because they say they're "getting cold drafts."

I'll count 30+ recessed lights into a cavernous ventilated attic or worse a roof-ceiling combination. When snow lingers for a few days I watch it melt between the rafters leaving perfect snow strips over the rafters.

I'll be there decorating inside and using a step ladder. The temperature stratification is so high in those spaces with "volume" ceilings that I PRAY everyone will leave so that I can open windows/doors IN WINTER to keep from sweating like I'm shingling a roof.

I gave up trying to explain to them about depressurization likely causing the drafts from the garage and how that huge range hood (when used) makes things REALLY bad and how all those recessed lights are making perfect little chimneys into the VENTILATED space.

The homes are nice and they are rightfully proud but I just go home, snuggle with a radiator and give the TRV a little pat on the head...

Then plumbing houses call me (knowing full-well that I'm no longer licensed) to fix problems with high-end installations, done (according to the homeowners) by the "best plumber in town." I NEVER ask the name!

It's amazing how many of these people seem to "plant" mortgage payments and utility bills prominently when they know we'll be there working when they're not around. Both are generally shocking to this poor boy.

One always takes me through the entire house showing me everything that has been done that year and making certain to mention how much was paid. She showed me a wall-to-ceiling built-in about 4' wide, 8' high and mentioned some outrageous figure, like five grand. It was nicely built and finished--about like mid-line kitchen cabinetry. Then she's in my house and sees the 8' wide by 9' high linen cabinet I built at the top of the stairs. She opens things and looks around and asks if I could build her something similar for around $2,000. That cabinet has a hand-rubbed finish, dovetail drawers, through mortises, extruded brass butt hinges, 100# drawer hardware, etc. I guess she though the solid wood clear finished drawer boxes and interior appointments were "cheaper" than her melamine covered particle board!

Ranting again...sorry. That time of year is arriving and I have to endure another season. At least the good ones--the ones that live in sensibly-built homes (old or new), make up for the wackos. One usually brings fresh cocoa, another good hot tea and if there late a glass of really good wine.

Annie Hall

Thanks Steve

You bring up another one of my worries -- the exhaust fan in the kitchen. We've spec'ed out a gas cooktop for an island, with an island hood overhead. The hood, like every other one I have seen for islands, draws 600 cfm. Other than open a window every time I cook, what do I have to do to be sure I'm not drawing exhaust from the boiler into the house? It sounds like you are saying that the fancy holes-in-the-wall approach may not be sufficient.

Steve Ebels

Definitely NOT!!!

I don't know the "volume" in your home but lets just say for example that it's 2000 sq ft with an average of 9 foot ceilings. That's 18,000 cu ft of air. Now what happens to a good tight house when you mechanically exhaust 600 cfm. That's the equivalent of completely removing all the air in the home TWICE in an hour. That is a huge heating/cooling load. It's also a huge amount of "unconditioned air" entering from somewhere. You need to make provisions for this hood because obviously the carpenter hasn't. An HRV system will may solve part of the problem but you really need to get a good HVAC guy in the picture and tell the builder "This is what we are going to do".

tim smith_2

high cap. kitch hoods.

Mike, you were talking about makeup air. Last year we did a 1400 cfm hood fan that customer liked to run alot, so we installed an Aero fan/coil unit tied to the boiler with 3 way mixing valve and Tekmar discharge setpoint control. Works great and holds 70 degrees great.

Annie Hall

Thanks Steve. I've been concentrating on the radiant heat system, and hadn't given much thought to the "V" part of HVAC. The contractor I've been working most with on the radiant package is from a company that only does radiant. I'll have to find someone else to tackle the ventilation issue, or choose a different radiant installer that can do everything.

Annie Hall

Tim, please explain

Tim, please explain this to me (obviously not in the trade) so that I can find someone locally to talk to about this.