Crawl space insulation

Ok, waiting to change planes, and for some reason the wireless connection keeps dropping. Here I go ... again

No, that isn't how a Heat Recovery Ventilator works. It's like central exhaust in that the HRV will extract stale air from places like bathrooms, kitchen (Range hood is *never* allowed to vent into HRV, it must vent outside separate), basement, laundry room, etc. The exhaust air passes through the heat exchanger core and is forced outside.

There is a second vent hood outside for intake air. The HRV draws fresh outside air in, through the heat exchanger core where it is warmed/cooled to near house ambient temp, and then usually put into the furnace return air duct. It's assumed you have a variable speed furnace fan running on low

It helps to cut a HEPA filter to fit into the HRV intake side of the heat exchanger core, it keeps outside dust out of the house. The HRV is usually naturally balanced, unless the intake vent hood ices up or is blocked by snow.

Otherwise, you have constant fresh air drawn into the house, and stale air exhausted

Geez, that's a huge vertical space. You'd be almost better off having two separate return registers, one near the floor and the other near the ceiling. Depending on season (Heat or cool) you'd switch which one to use. That is common around here for such tall vertical spaces

That's ideal. A typical Flatlander home site the rim is usually no more than two feet above finished grade.

Condensing gas furnaces have forced induction. Obviously I don't have the book in front of me, IIRC something like 40 ft of pipe run is allowed for intake and/or exhaust PVC. I will look this up once I return next Wed.

It would be no worse than a regular gas furnace + hot water heater on the same stack. Around here, once it's -30 and colder, you see a giant sculpture of ice around the cap at the top of the roof.

I do know of somebody who vented their direct vent gas furnace out the roof. No issues whatsoever, even at -40

Again, once I return next week, I'll dig out the Bryant book and get the true figures

 

Once the furnace locks out - it *will* lock out if it can't "prove" combustion air with the inducer - you not only have to trudge out and clean the snow out, you have to power cycle the furnace to reset it

The smarter networked furnaces, like my Bryant Evolution Plus 90i, will display the error in the LCD screen of the thermostat. So you can recall the error, mumble "well, f*** a duck," at least that's what I usually mumble, dress up like Nanook of the North, trudge out in the middle of a blizzard, shovel the snow drift away from the intake and exhaust hood, trudge back inside, power cycle the furnace, and wait for it to go through it's startup routine

I also bet you a bottle of gin that the guy who put in your furnace, never explained to you that you would have to trudge out there to keep snow drifts away from the intake hood. Did he? As a temporary measure, you can try to put up that ugly orange snow fencing around the intake hood, at least 10 ft in front to keep the drifts away

Do you have the combination intake/exhaust hood collar, or two physically separate ABS pipes? If you have two separate ABS pipes, then believe it or not, you're in luck.

You can actually glue together a stack extension to the intake pipe, extend it say 3-4 ft above grade. My Bryant install manual has detailed instructions on this, if you're willing to wait until I get back, I can scan and email it to you

If you have the combined intake/exhaust collar outside, you're SOL

Ok, had better wrap this up, they will start boarding soon

 

All true. We have separate intake and exhaust just for that reason. Mostly we don't have much trouble, due to protection from the building and shrubbery. I walk to the store and post office at least once a day, which gives me an excuse to look at both vents. If the snow is getting close, I knock it down before it becomes a problem. Of course that doesn't take care of big storms, but that's another issue.

So jayman, where are you off to this time?

Tom

 

Besides the attic fan, there's a padded foil roll out material you can staple onto the inside of your attic roof that'll really help drop summer temps. check your local home depot / lowes.

 

That's how I would have designed it and dual zone as well. The sub-basement is open to the walkout and that to the main space above. (3-2 split half levels with a high ceiling in the entrance/living/dining.) The cold air sinks into the sub and has no flow path out...while hot air introduced by the register there can follow the ceiling back out and up.

Having the heated air introduced at the top of the walkout basement level doesn't help either. And of course the concrete slab floor in the walkout is well carpeted providing some R value, but not enough to prevent a substantial floor to ceiling temp gradient.

As it is I adjust the registers so that the upper levels are open in Summer and throttled in Winter, with the reverse being done for the lower level registers. In fact, I had virtually all the lower registers closed during Summer to reduce stratification. The large open stair well serves as the pressure/flow balance. In Summer I left the blower on continuously as well. It's an old inefficient single speed blower and pulls about twice the amps that I anticipated (can't see the name plate on it, measured the load from the electrical meter...need to do a retest.)

True, but I've also read of problems with long vertical runs for them and reduced furnace life. What I had looked at so far suggested short vertical runs.

There is still a lot of natural draft with a regular gas furnace and a tall stack (in addition to the ID fan), and you just won't have that with the condensing system. Since most of the stack is passing through conditioned space the wall losses aren't as severe either.

 

R-6 seems to be pretty standard in the stores around here. It probably has to do with the thickness that would be required to go higher. R-6 starts getting bulky on ducts anyway. If the duct piping is run between joists it can be tricky to fit even R-6. R-13 or R-19 would be really thick.

I've been surprised at how few manufacturers there are for this sort of thing. Seems to be a very non-competitive market.

 

Tripp,

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As for duct insulation,,I'll leave it to the HVAC experts, but I would consider R-6 is pretty puny. I would add as much as you can. Do a bit of research on which kind is best. Remember, the heat loss out from any materiel is a function of the R-value AND the difference in temperature between spaces. (Delta T) With any given R-value the amount of heat loss will be greater with a greater Delta T. So in a heating environment like a crawl space, anything you can do to reduce the Delta T will reduce the heat loss. Keeping foundation vents closed and the ducts away from drafts is a big help. There are "whole house" plenum systems that pressurize the entire crawl space with warm air, allowing the air into the room through registers. This requires a well insulated foundation wall, as well as a well insulated ground/grade cover.

I am really not a fan of forced air heat as parasitic energy coupled with duct losses and potential inefficiency.


Icarus

 

You get most of your return out of the first few R units anyway. Don't get me wrong, I would prefer high R value, but going from essentially R-1 to R-6 you will knock the losses down to ~17% of their former value. If you double that to R-12 you get down to only ~8% compared to the insulated base. Your cost of insulation will double for no more than a 9% net gain as opposed to half the cost for the other 83%. If one is starting from an R-6 base, then going to R-12 is impressive.

If you find a product that will give you a much higher value and works well in an open crawl space then I sure wouldn't want to discourage you from trying it, and reporting back to let us know what you think of it. But, you will probably get more benefit from surveying what is available (maybe call an HVAC contractor to see what they do for energy efficient builds?) and doing it sooner rather than waiting. If you wait a month losing 83% it will take over nine months of actual heating season to make up the difference of installing insulation that is twice as effective...ouch!

I used a bag of this product, ~15 square feet labeled R3, on my main rectangular discharge duct. The stuff is kind of pricey so I don't think it would be cost effective to put it on the round ducts--although like you I was considering it. I was trying to cut down the heat/cooling gain in my large utility room as it does me no good for it to be 10 degrees hotter than the adjoining hallway in Winter and 10 colder in Summer (about 2/3 of the surface of the room are to external sinks.) This, jacketing the water heater, insulating hot water piping, and sealing many gaps in the ductwork in this area has cut the delta T of the room in half during max heating loads. (Keep in mind this is with an unsealed, 80% furnace and ~65% water heater with about 10 feet of flue piping in the room.)

I used some approved foil tape for the seams when I applied this material. Part of what I was doing was trying to slip some in to partition the discharge and return ducts that lay side by side--difficult to do with tight clearance and a sticky, curling material.

I'm not sure what to make of the result of this particular change. The material has noticeable thermal mass and that's not really desirable in the discharge duct since it cycles. I was hoping the foil surface would feel relatively cool, but instead it seems to retain palpable heat that is then slowly expelled to the room after the blower shuts down. So effectively it cannot be R3 in my installation. Oh well, it isn't hurting, just not helping as much as I hoped.

 

I really don't know,, but my intuition says that the smallest heated envelope is the most efficient. On the other hand,,, it has been suggested that since the earth temperature is relatively constant, and if you insulate the stem walls well, then you could (and people do) make the argument that you are heating the crawl space from a much higher starting temp, and therefore it is more efficient. My problem with that is that it is very hard to make a perfectly sealed crawl space, and if you do, you are creating other potential problems,,, like radon, potential mold etc.

As I said before,, if it were me I wouldn't have forced air, but if I did, I would insulate the floor to at least R-19, vent seasonally as needed, cover soil with proper vapor barrier, and insulate my ducts to the max.

Look into foilfaced bubble wrap. You can wrap it easily over ducts, it is clean and has a comparatively high r-value and it is resistant to moisture.

Icarus

 

I just got back and have the Bryant install manual in front of me. This is for their Plus 90i direct vent furnace. First , the manual claims that roof termination is preferred.

Second, depending on the size of the furnace, and weather you use 2 inch or 3 inch, you're allowed anywhere from 42-70 ft of pipe run

If you use too large a pipe, the manual warns you could have problems with the furnace proving flame. In all cases, the length is dependant on the number of 90 degree elbows, and the pipe diameter must be correct - not too big or too small - for the intended length

The manual has a very clear table that lists operating elevation, furnace size, pipe diameter, and number of elbows.

 

We were at the Ineos refinery in Grangemouth, Scotland, and the Statoil refinery in Mongstad, Norway (Technically, we were at the CHP facility at Mongstad)