HVAC dilemma

[EbS-P]

Well just got the first quote back. Not super confident as contractor thinks I have gas heat which I don’t and ignored my request for a dehumidifier. 6500$

Remove entire duct system and replace. Because it has Gas heat. Duct all the way to the Unit must be replaced. Hard duct on supply because of discharge air temp, no flex for first 6'. replace using R 8.0 Wrapped supply trunk. R 8.0 Flex supply runs. New Boots and grills. Hood will have to be removed and new hood build. Job will take a full duct crew 1.5 days to complete.

Another one come to look at it Friday. Need to make some more calls. Maybe I just need to suit up and go down into the crawl space my self. I could replace the run in the basement myself. If that’s the only duct board then I could just have the system cleaned, sealed and call it done saving 5k.

 

[vbu]

What is the reason to replace any duct work at all (other than sealing)? I'm personally not a big fan of flex lines.
Our house has all square ducting. However they must've sized something wrong when they built the ductwork because every time the air/heat comes on all the ductwork 'plops'. Square ductwork gets either sucked in or pushed out, not sure in which run it is.
I would personally avoid that contractor as he doesn't seem to have too much attention to detail since he ignored your request for a dehumidifier.

 

[EbS-P]

What is the reason to replace any duct work at all (other than sealing)? I'm personally not a big fan of flex lines.
Our house has all square ducting. However they must've sized something wrong when they built the ductwork because every time the air/heat comes on all the ductwork 'plops'. Square ductwork gets either sucked in or pushed out, not sure in which run it is.
I would personally avoid that contractor as he doesn't seem to have too much attention to detail since he ignored your request for a dehumidifier.

All the ducts are original to 1968. Half the system is duct board and can’t be cleaned and is very dirty. Moldy?? Don’t know didn’t bother testing. Insulation is not good and falling off in spots. All the 900 sq ft CS needs re insulated (floor joist) or it needs encapsulated and insulated. No moisture barrier and quite tight quarters in spots ducts almost on the ground. A diy project if I cleared all the ducting out. Otherwise I’m paying to have it done.

Reason I called him I can see his house/shop two doors over. He’s running two trucks now. Running the whole thin himself. Seems like a good guy that could do decent work. A little sloppy on the business side/customer PR side.

 

[stoveliker]

I would be hesitant using a neighbor. Best to keep the relation neighborly - and with paid work, you should keep it business-like. I think the two don't mix well.

 

[EbS-P]

I would be hesitant using a neighbor. Best to keep the relation neighborly - and with paid work, you should keep it business-like. I think the two don't mix well.

Never spoke a word to him until he came over for quote. My hope was he’d be a bit more careful looking at the job he did everyday.

 

[RockyMtnGriz]

Not stirring anything - I've been looking at this thread trying to learn and satisfy curiosity.

Looking at my thermometer doodad, it says 6 degrees F outside and 61% RH, 58 inside, and 31% RH. It reads a little low on the RH - especially the outside one. Weather Service says 2, 82% and -2 dew point. They're a few miles away, though I still guess that humidity must be a little different in China? But it's close enough.

Anyway, I'm obviously not going to figure this out for myself living here.

I'm trying to understand the advantage of the dehumidifier over just running the AC. I get the short cycling problem, but isn't that just the wrong size AC unit? Doesn't it take about the same energy to get the same amount of water out of the air? Why would it matter if you dump the heat from the water inside or out? Yes, it will be a little more efficient if the condenser is right after the evaporator, and putting the heat back will lower the inside humidity some, but at the price of getting the heat back - how is that worth it?

Is it that much more efficient than just say setting the AC on 63 and letting it crank away? That at least sounds more comfortable.

Again, I have no experience with this, I'm just curious - not that I can actually explain why!

 

[EbS-P]

Not stirring anything - I've been looking at this thread trying to learn and satisfy curiosity.

Looking at my thermometer doodad, it says 6 degrees F outside and 61% RH, 58 inside, and 31% RH. It reads a little low on the RH - especially the outside one. Weather Service says 2, 82% and -2 dew point. They're a few miles away, though I still guess that humidity must be a little different in China? But it's close enough.

Anyway, I'm obviously not going to figure this out for myself living here.

I'm trying to understand the advantage of the dehumidifier over just running the AC. I get the short cycling problem, but isn't that just the wrong size AC unit? Doesn't it take about the same energy to get the same amount of water out of the air? Why would it matter if you dump the heat from the water inside or out? Yes, it will be a little more efficient if the condenser is right after the evaporator, and putting the heat back will lower the inside humidity some, but at the price of getting the heat back - how is that worth it?

Is it that much more efficient than just say setting the AC on 63 and letting it crank away? That at least sounds more comfortable.

Again, I have no experience with this, I'm just curious - not that I can actually explain why!

ACs are most efficient if they keep the coil above the dew point. This isn’t practical (but some of the new mini splits in eco mode try and do this. ). A dedicated dehumidifier is more efficient at removing water than the AC. 70% of rated capacity (rule of thumb) for an AC cools the air (this is sensible capacity) . The other 30% of the energy is what must be absorbed (by the refrigerant) due to the latent heat released during condensation. This all depends on the out door temp (dry bulb ) and the indoor dew point (wet bulb) and indoor temp (dry bulb). Here is the data for my unit. Today it’s 73 outside with 80+% RH. (93% right now.) insides it’s 73 with 65% rh. It will cool off tomorrow and we will need heat but if we don’t remove the moisture as the indoor temp drops the RH increases. So while we could run the AC and do September and October we still need humidity control November-March. And I don’t see the point of running the AC for an hour then the heatpump for an hour.

The heatpump water heater moves the indoor heat to the water and blows cold air out. It usually runs the coil below dew point which is good because it uses that latent heat to heat the water rather than wasting it like the AC. And dehumidifies too. Most of the country winters are dry but not here. the ocean is still 68 degrees!

While you need a kettle on the stove December-March we still need to dehumidify. And it’s too cold to run the AC. 5 kids and dog we open the doors a lot.

 

[Corey]

...
I'm trying to understand the advantage of the dehumidifier over just running the AC. ...

I think this is sort of an apples/oranges comparison. Sort of like asking the advantage of running a furnace over an air conditioner. They are doing different things, so there is not really an 'advantage' of one over the other.

If you need the air to be dyer, but with no drop in temperature, or even a slight increase in temp, then your dehumidifier is the go-to appliance. If you need the air to be cooler and lower in humidity, then your air conditioner is the appliance to use. A dehumidifier is literally just an AC unit that doesn't poke its 'hot end' outside, so just dumps all the heat in the room.

As mentioned above - each one is pretty efficient for what it does, though when you try to cross functions, they can lose efficiency. I've also noticed somewhat of an 'intermediate' step on various air conditioners where they use condensate from the coil to generate additional cooling of the incoming freon. My Whirlpool AC from 1973 did this. Seemed like the practice may have fallen out of favor in the 80's / 90's (or at least I never saw it in my limited experience) but I just noticed some window AC units which were dipping some of the condensing coils in a trough of condensate water. So seems like it is back.

 

[EbS-P]

I think this is sort of an apples/oranges comparison. Sort of like asking the advantage of running a furnace over an air conditioner. They are doing different things, so there is not really an 'advantage' of one over the other.

If you need the air to be dyer, but with no drop in temperature, or even a slight increase in temp, then your dehumidifier is the go-to appliance. If you need the air to be cooler and lower in humidity, then your air conditioner is the appliance to use. A dehumidifier is literally just an AC unit that doesn't poke its 'hot end' outside, so just dumps all the heat in the room.

As mentioned above - each one is pretty efficient for what it does, though when you try to cross functions, they can lose efficiency. I've also noticed somewhat of an 'intermediate' step on various air conditioners where they use condensate from the coil to generate additional cooling of the incoming freon. My Whirlpool AC from 1973 did this. Seemed like the practice may have fallen out of favor in the 80's / 90's (or at least I never saw it in my limited experience) but I just noticed some window AC units which were dipping some of the condensing coils in a trough of condensate water. So seems like it is back.

Split system dehumidifier are starting to be sold. Not sure the market but it would be much further south than here.

 

[vbu]

Is it that much more efficient than just say setting the AC on 63 and letting it crank away? That at least sounds more comfortable.

The problem is that that doesn't cut it. Ok we turn the air down to 63 and we get some dehumidification, then what? The house is cold and still humid. Sometimes I wish I could run the AC while the heat (gas)is going at the same time lol. That's why you use a dehumidifier, to keep the heat inside of the house and get rid of the moisture. I'm in North MS so not close to the ocean, so I'm sure its a lot worse for Ebs-p, but it's still a fight here. Thinking about putting a new vapor barrier in myself, but I really dread getting rid of the old one and cleaning up in there (rodents got in there at one point, they're all gone now but left some stuff behind). May just have to get a quote to see how much something like that would cost

 

[EbS-P]

Two contractors were no shows today (one HVAC one window). Batting .500 for today. .375 over all.

Contractor that came we have used and are qualified no nonsense operation. Agreed all the duct boards gotta go. Really didn’t think separate duct trunk for the basement was needed. If what we have has worked for 12 years and it was a quick remove and replace when it was installed in 2009. So sizing everything to the manual J,S, and D will only make it better. Adding a basement return will help.

I am guessing I will be the first customer of his to tie heat-pump water heater into supply duct. But I’m confident they can do the job well.

 

[EbS-P]

The problem is that that doesn't cut it. Ok we turn the air down to 63 and we get some dehumidification, then what? The house is cold and still humid. Sometimes I wish I could run the AC while the heat (gas)is going at the same time lol. That's why you use a dehumidifier, to keep the heat inside of the house and get rid of the moisture. I'm in North MS so not close to the ocean, so I'm sure its a lot worse for Ebs-p, but it's still a fight here. Thinking about putting a new vapor barrier in myself, but I really dread getting rid of the old one and cleaning up in there (rodents got in there at one point, they're all gone now but left some stuff behind). May just have to get a quote to see how much something like that would cost

Going to get some quotes for a full encapsulated crawl space. I’m guessing in this market it will break the budget. So im mentally preparing to do it myself.

 

[vbu]

Going to get some quotes for a full encapsulated crawl space. I’m guessing in this market it will break the budget. So im mentally preparing to do it myself.

yep, same here. I wouldn't even know who to contact around here for encapsulation. There's one area in my crawl space where they dug down, so you could go under the ductwork over to the front part of the house. I've seen that flood before after a heavy rain, and I don't know how to tackle this. I did some grading work in that area this summer, hopefully that fixed my problem

 

[EbS-P]

yep, same here. I wouldn't even know who to contact around here for encapsulation. There's one area in my crawl space where they dug down, so you could go under the ductwork over to the front part of the house. I've seen that flood before after a heavy rain, and I don't know how to tackle this. I did some grading work in that area this summer, hopefully that fixed my problem

https://youtube.com/c/CrawlSpaceNinja

They have lots of info

 

[vbu]

https://youtube.com/c/CrawlSpaceNinja

They have lots of info

Oh you're going to lead me down a rabbit hole now... lol. Thanks for the link I'll check it out

 

[RockyMtnGriz]

Thanks for the explanation, folks! I'm glad I don't have your problem! I probably could have used a dehumidifier for west coast damp and foggy Cascade winters. It might have cut down on the need to mop up the condensation on the windows regularly. Here it just freezes into pretty wheat patterns when it's cold enough, then evaporates away when it warms up.

You did get me thinking that if you had a HPWH and put a heat exchange loop on it so that it just kept running, while dumping the excess heat back above a water temperature that you could live with - say 114, you'd have both a water heater and a dehumidifier in one. It wouldn't be as efficient as a stand-alone dehumidifier, because the condenser temp would be elevated to 114 rather than room temp, but it might make sense for occasional duty - maybe... Depending on the amount of uninsulated piping in a house, I wonder if it could be as simple (in some houses while near impossible in others) as adding an instant hot water circ pump system and running it off of a tank thermostat when you want dehumidification? You'd also get the usually very wasteful side benefit of the instant hot water during that time.

I suspect that heavily subsidized HPWHs are going to be much more available soon. Not that I agree with that, but at some point, you gotta work within the prevailing system.

 

[EbS-P]

Thanks for the explanation, folks! I'm glad I don't have your problem! I probably could have used a dehumidifier for west coast damp and foggy Cascade winters. It might have cut down on the need to mop up the condensation on the windows regularly. Here it just freezes into pretty wheat patterns when it's cold enough, then evaporates away when it warms up.

You did get me thinking that if you had a HPWH and put a heat exchange loop on it so that it just kept running, while dumping the excess heat back above a water temperature that you could live with - say 114, you'd have both a water heater and a dehumidifier in one. It wouldn't be as efficient as a stand-alone dehumidifier, because the condenser temp would be elevated to 114 rather than room temp, but it might make sense for occasional duty - maybe... Depending on the amount of uninsulated piping in a house, I wonder if it could be as simple (in some houses while near impossible in others) as adding an instant hot water circ pump system and running it off of a tank thermostat when you want dehumidification? You'd also get the usually very wasteful side benefit of the instant hot water during that time.

I suspect that heavily subsidized HPWHs are going to be much more available soon. Not that I agree with that, but at some point, you gotta work within the prevailing system.

Based on experience a large family can count on the HPWH to dehumidify 500-800 square ft to 55-65 RH.

 

[EbS-P]

Got the crawl space encapsulation quote come in at 11k$. Crawl space ninja’s. It’s high, but not unreasonable, no clue what the markup. I don’t see how I can finish the project (no other quotes back yet) with in budget if I pay to have that done. Looks like another DIY project.

I was prepared for 8 k max. I guess I have to decide if windows or encapsulated crawl is more important? Or see what I can manage by myself.

In the plus side there was almost no mold or fungal growth. They looked really hard and bound a few specs.

 

[vbu]

It's funny that you post this today because I got my quote back yesterday. Around 2K for vapor barrier, little north of 10K for encap. When I get serious about doing it (aka have enough money) I'll get some more quotes but I'll probably end up doing it myself. Insulation has to come out because it's wet. They did find some fungus/mold spores and they said it looked like it had been treated before. Too bad someone else already paid for the treatment but didn't correct the cause.

I may just put a vapor barrier down and call it a day. We don't plan to be in this house for more than 5 years from now so I don't think encapsulation is a good investment, unless I DIY it

 

[fbelec]

i don't know if you guys use thumbtack but i see alot of insulation guys up here giving quotes. you probably get quotes back seeing as the contractor has to pay for those leads.

 

[alber197]

I'm an plumber/gasfitter who also does some HVAC work (in MN/WI so different climate) so I'll give my 2 cents here...

Your current unit is undersized as you know. Encapsulating your crawl space will help but won't change the fact that you have an undersized unit (maybe over or undersized ductwork). You may spend 10k encapsulating and that won't change your heating problem (it will probably help with the humidity though).

You need someone to come in and do a full manual J and then manual D off of that. Where I'm at most HVAC companies don't do those. They just use "rule of thumbs" or replace same to same (or next size up if there is heating or cooling problems). If you put in bigger unit with more CFM on the current ductwork than that creates a whole another set of problems.

If it were me, I would find a company to do a manual J and have them run it with options for crawl space as is and encapsulated/insulated. That may help you decide if it's worth it.

An online rescheck/manual J is one option if you can get them the proper info (he will need plans, info on windows, insulation, etc.). I used this one in the past: https://www.rescheck.info/2017/05/11/do-i-need-a-rescheck-manual-j-or-both/.

Alot of smaller 1 man shop HVAC companies use this to satisfy code requirements for permits when installing new systems because its so cost effective. I used it to properly size our cabin when converting from electric baseboard heat to forced air. For 79$, it won't be 100% perfect but will get you in the right direction.

Regarding the dehumidifiers, as others had mentioned they will heat up the space unless ducted outsized or to an area that can use the heat. A whole home dehumidifier will certainly help. They tend to not last very long so I would be hesitant to spend a ton of money on that. A properly sized cooling unit will dehumidify the space (but not the open crawl space.)

Lastly, if you have duct board in that crawl space, it probably needs to be replaced. We don't used duct board or much flex here because we have full basements but insulated flex would be a good option for you if you need to replace the ductwork. It's cost effective and when installed correctly works well (pulled tight, minimal turns, no sags, dips, etc.).

Hope this helps.

 

[EbS-P]

It's funny that you post this today because I got my quote back yesterday. Around 2K for vapor barrier, little north of 10K for encap. When I get serious about doing it (aka have enough money) I'll get some more quotes but I'll probably end up doing it myself. Insulation has to come out because it's wet. They did find some fungus/mold spores and they said it looked like it had been treated before. Too bad someone else already paid for the treatment but didn't correct the cause.

I may just put a vapor barrier down and call it a day. We don't plan to be in this house for more than 5 years from now so I don't think encapsulation is a good investment, unless I DIY it

House was built in 1968. The CS is in decent shape for a vented CS in the south. I think I will seal the vents and add a 200$ dehumidifier and see what happens. I know it’s not the best way but spending 3-4k$ just on dehumidifiers for my house at once is a lot. Probably will add 30$ or more a month to my lower bill.

I’ve got time to do it right. One step at a time. I’m not goin to rush and do it before ducts get redone.

 

[EbS-P]

I'm an plumber/gasfitter who also does some HVAC work (in MN/WI so different climate) so I'll give my 2 cents here...

Your current unit is undersized as you know. Encapsulating your crawl space will help but won't change the fact that you have an undersized unit (maybe over or undersized ductwork). You may spend 10k encapsulating and that won't change your heating problem (it will probably help with the humidity though).

You need someone to come in and do a full manual J and then manual D off of that. Where I'm at most HVAC companies don't do those. They just use "rule of thumbs" or replace same to same (or next size up if there is heating or cooling problems). If you put in bigger unit with more CFM on the current ductwork than that creates a whole another set of problems.

If it were me, I would find a company to do a manual J and have them run it with options for crawl space as is and encapsulated/insulated. That may help you decide if it's worth it.

An online rescheck/manual J is one option if you can get them the proper info (he will need plans, info on windows, insulation, etc.). I used this one in the past: https://www.rescheck.info/2017/05/11/do-i-need-a-rescheck-manual-j-or-both/.

Alot of smaller 1 man shop HVAC companies use this to satisfy code requirements for permits when installing new systems because its so cost effective. I used it to properly size our cabin when converting from electric baseboard heat to forced air. For 79$, it won't be 100% perfect but will get you in the right direction.

Regarding the dehumidifiers, as others had mentioned they will heat up the space unless ducted outsized or to an area that can use the heat. A whole home dehumidifier will certainly help. They tend to not last very long so I would be hesitant to spend a ton of money on that. A properly sized cooling unit will dehumidify the space (but not the open crawl space.)

Lastly, if you have duct board in that crawl space, it probably needs to be replaced. We don't used duct board or much flex here because we have full basements but insulated flex would be a good option for you if you need to replace the ductwork. It's cost effective and when installed correctly works well (pulled tight, minimal turns, no sags, dips, etc.).

Hope this helps.

It’s does thank you. I was up front with my HVAC contractor that I want a full load calc. The reason being that I don’t think they have ever tied a HPHWH into the supply duct. Add the whole home dehumidifier and it’s adding 4-600 cfm of intermittent flow to the supply side. And that really needs accounted for in my opinion. Is this an easy entry in the manual D?

And I’m not really super concerned about the load calc. The old unit is comfortable 95% or more of the time and fixing duct leaks will get me more a decent bit of capacity back into the house. But it’s going to need replaced some day and have appropriately sized ducts for the correctly sized future unit I think is important.

 

[alber197]

It’s does thank you. I was up front with my HVAC contractor that I want a full load calc. The reason being that I don’t think they have ever tied a HPHWH into the supply duct. Add the whole home dehumidifier and it’s adding 4-600 cfm of intermittent flow to the supply side. And that really needs accounted for in my opinion. Is this an easy entry in the manual D?

And I’m not really super concerned about the load calc. The old unit is comfortable 95% or more of the time and fixing duct leaks will get me more a decent bit of capacity back into the house. But it’s going to need replaced some day and have appropriately sized ducts for the correctly sized future unit I think is important.

Yes anything can be accounted for in the manual D but you can't do a manual d without a manual J first.

If your unit is comfortable 95% of the time, I don't think you need a manual D as long as the extra cfm is accounted for in the new ductwork. Installation of new ductwork and proper air sealing in your home will probably make up the difference. The installation makes all the difference in the world. Even with a proper load calc or manual d, it can all be messed up with a poor install. I'd try to find an installer that finds useful solutions to your issues that you trust and go from there. Implementing a perfect load calc or manual d in the real world is not always possible either.

Also, if you are pushing that much extra CFM into the supply, you will want to account for it in the return sizing also (you can never have too much return air and it's almost always grossly undersized).

Problem will be finding any HVAC contractor willing to do load calc or manual d (for sure not a manual D, they are almost never done is residential installs where I'm at). If everyone is as busy in your area as they are here, they will just move onto easier jobs if you ask for both of those.

Start by getting a Manual J and go from there. Duct sizing is relatively easy at that point when you have correct individual room loads and friction rate. And again, almost all existing ductwork is undersized, espcially when paired with newer units.

If you don't want to submit the info yourself to an online rescheck company, look at having an energy audit company or someone similar come and look. They usually have the skills and tools to do a proper load calc. I think this was mentioned by someone else also.

Again, hope this helps. Good luck.

 

[EbS-P]

Latest and probably last quite came in today. 12k for new ducts and a whole house dehumidifier. 8500 for ducts 3500 for dehumidifier. Probably 1000$ more than I was expecting (mostly for the dehumidifier). The company has been my regular HVAC company. A down to earth company that hasn’t ever tried to up sell me or my father. They will get the job.

Details need to be worked out like can the basement main dice be sized so I can use standard height interior door?? Where the basement return going to go. What’s the best way to duct the dehumidifier and HPHWH??? I probably will have a more active role in planning this than the the average home owner getting new ducts.