Thanks tigerdunes!

Luckily, I have some more information now :)

- the house is a 2 level split design on concrete slab.

- the furnace is in the center of the house on the lower level

- furnace and hot water tank share one exhaust straight up through the roof

- current furnace is Weatherwise 110000 BTU, 40 yrs old

- a large vertical duct comes from the furnace and turns into a 7x14 horizontal duct. From it, 5" ducts come off. No more ducting is visible its all behind walls :(

Today I had another guy come by. He recommended a 70000 BTU 2 stage lennox 96% efficient furnace base don the size of the house.

He says the air intake and exhaust can run in the basement ceiling / floor horizontally (!) to the outside of the house.

Condensate can also run to the outside of the house.

I asked several times and he insists there will be no issues with small ducts or , whistling and condensate or anything.

It sounds a bit too good to be true .... and I still wonder:

- will my ducts be big enough? If I have to replace plenums or ducts in my house I am screwed as half the walls would have to be taken out

- can the furnace exhaust run near horizontally in the floor or does it need to be slanted?

- will the exhaust eat my aluminum siding? ( I was told it would by anther expert)

- is the furnace a good choice or should I go for a different or more efficient model?

- is there any special grade exhaust piping I need to look for? I hear there are different grades

- Is there anything that may come back to bite me? With a new hot water tank and discount I will pay $4500 which i can do but if there will be follow up cost for issues it would screw me

Edit: distance from the furnace to the outside wall is 10 ft and the rafters are 9" high. I found out there should be a 1/4" slope per foot so if the exhaust piping isnt overly large it should go in there with good enough slope....

It was suggested to get a 2 stage Lenox furnace but now I am thinking to get a modulating one instead ... I will keep the house for a while so it may be worth the extra comfort ...

:) Matt

This post was edited by Matt499 on Thu, Sep 25, 14 at 2:10

Old houses like yours are likely to have over sized furnaces. If the duct work was sufficiently sized for the 110K BTU furnace, then it should be fine for a new 70K BTU size. The contractor should measure the main supply and return and inspect for any leakage at the joints. Spending some money on having joints sealed where needed is a good investment.

The PVC exhaust and intake need to rise up from the furnace and to the outside along the ceiling. The exhaust needs to be pitched back towards the furnace. Your size furnace would probably use a 2 inch PVC pipe. The required size is specified by the installation manual.

There is nothing special at the PVC pipe. The condensate is slightly acidic, but it will not harm old aluminum siding. The exhaust and intake can't be placed near a window or door. The rule is usually a 3 foot minimum distance and the two PVC pipe openings need a least a foot of separation. The pipe openings should be at least 3 feet above ground level but it may need to go higher if you get high snow drifts.

The main thing that can come back to bite you is a poor installation. Ask a lot of questions and make sure they make sense to you. Make sure you get all the model numbers of the equipment and work to be done specified in the agreement. I would want to see a load calculation to verify the sizing.

I generally agree with Mike.

How was the furnace size quoted determined?

Can you describe typical winter climate and temperatures?

What model Lennox furnace and thermostat quoted?

Post back.

IMO

thanks guys!

he asked the square footage of the house and did a quick calculation and compared the result to the 110000 btu unit and its efficency. I cant remember but I think there was a 50k model and the 70k, he recommended the 70k BTU.

The winter here are mild for the most part temp is around freezeing, maybe 23-40F.

he quoted a EL296 UH0 70XV36 with the cheaper LCD thermostat from lennox. the icomfort would be $700 or so more but I can get it on ebay for 300-400 and just have him install

I asked to check or measure the old ducts. He did not recommend it. Forgot why. Since you cant access my ducts its no point anyways probably ...

It sounds like the exhaust isnt an issue then :) with a 2" pipe there should be enough space to have slope.

is it normal to pipe the condensate out to the side of the house as well?

I asked how much the modulating furnace would cost and it would be about $700 more. But they say it would not work well for my house and the older ducts and airflow can drop.

It is either good they wont upsell me something that wont work or they may just want to sell what they have sitting in stock ...

Another contractor recommended the modulating SLP 98 UH070XV36B

I had 3 guys here and each says something else ...

I have not found anybody who was even remotely interested to do a load calculation or measure anything.... I got an HVAC size calculator software and understand why ... it is very complex .

Many people here say it is too mild to worry about a furnace much.

:) Matt

Some internet research shows that the lennox slp98 had issues when it came out ... maybe this modulating business is just complex and prone to break.

maybe I am better off with the simpler 2 stage model .... less stuff to break

Average age of furnace is 15-18 if properly maintained. But as you telling its 40 year old. So I would suggest to buy a new one or you can take advice of professional technician who will tell you what will be the best.
And rather than spending so much in repairing, buying a new furnace will be a good option.

Here is a link that might be useful: Furnace Installation Toronto

I would want to see a valid and professionally performed load calculation in writing.

Don't care for Lennox nor that furnace selection. If you intend to be in this home for the foreseeable future, you can do much better than this. Invest in quality and comfort especially since AC is not involved.

IMO

The comment about a modulating furnace not working well in your house with old ducts and air flow would drop makes no sense. I suppose this contractor does not like installing modulating furnaces. A 2-stage furnace is fine with your mild winters and the fact you don't have an AC.

Two stage furnaces require true two stage thermostats for full functionality. Not a cheap thermostat that works off a timer or algorithm and will always go to high stage whether needed or not.

The comment on modulating furnaces is ridiculous and in fact these mod furnaces would be a great choice for your application.

IMO

So I understand the dealer is BSing about the modulating one not working...

If I ask that dealer to install modulating furnace then he will blame all issues on that ....

problem is that I am running low on dealers, the two I had here were the largest lennox dealers with 20 or so years in the business.

Nobody seems keen on doing load calcs or look at the ducts, let alone measure something....

Looking forward, at least it seems that my ducts should be ok ...

If I dont get Lennox what brand should I get? Modulating furnaces are about 800 more, which i would be willing to spend, unless there is not much difference.

I do have vaulted ceilings and getting those rooms heated is always difficult so may a modulating furnace would help...

What is there for a dealer to screw up with the installation that I should look for?

If anybody can recommend a dealer in the GWA, it would also be appreciated

It seems we only have the following things down:

- my ducts should be ok

- exhaust should be ok to do

Qs:

- what brand furnace to get?

- 2 stage or modulating?

- where to find a good dealer

- what to look for during install

:) Matt

You can look at Carrier and sister company Bryant, or Trane and sister company American Standard. Go to each web site and see if there is an authorized dealer in your area.

would a trane furnace be much better or different over a lennox? What are the differences?

Yes, I think either Carrier/Bryant and Trane/AmStd are better choices in quality than Lennox. That's my opinion, others have theirs.

The comment though about the modulating furnaces from the Lennox dealer really is absurd.

If you don't want a mod furnace, then the next choice would be a two stage high eff var speed model. I still would look at a mod furnace though since heating will be your only HVAC plus ductwork is not accessible.

IMO

Guys on the internet say the lennox will only modulate UP but not DOWN .... this seems a bit like a pathetic design.

Maybe I better go with trane then (assuming it modulates up and down)

You want a mod that modulates both up and down and adjusts as outside temperature changes. All these mods require same brand proprietary controller.

I would not have the Lennox.

IMO

which brand should I get? Does trane modulate up and down?

Here is a little primer on modulating furnaces.

I suggest you contact a Trane/AmStd or Carrier/Bryant dealer.

Here is a link that might be useful: Primer on Mod Furnace

I am looking for a trane dealer.... looking at this primer it would make the lennox furnace quiet useless if it only modulates up. Although I am not sure who could be dumb enough to design something like that and think it might not be true and based on a defective unit

I am not a Lennox expert, but it could be other things going on with the set up your read about. First the system may have a basic single stage thermostat. In this case the modulation would be done be a timer on the furnace control board. The furnace starts in the low stage and goes up in stages at fixed timer intervals until the thermostat is satisfied. This is a bad set up a complete waste of a modulating furnace.

The other possibility is the furnace does not have an algorithm built in to tell furnace to modulate up and down. It could be a simple algorithm that always starts at the low stage and moves up depending on the temperature differential. The thermostat keeps the furnace at a set stage until the temperature is satisfied.

You can buy the best furnace on the market, but if you don't buy an appropriate thermostat the furnace can never operate at its maximum potential.

Good post by Mike.

And I will add it is a disservice to upper end furnaces not to use the appropriate thermostat for full functionality.

Too many times a dealer cheats both a nice furnace and the homeowner by knowingly installing the wrong thermostat/controller. Plus sometimes homeowners want to take a cheap shortcut that ultimately will cost them in the longrun both in comfort and operating cost.

Not a fan of these lifestyle thermostats/gadgets either.

TD

I kept reading a bit more and indeed it seems that the lennox only upmodulates with a wrong thermostat but will work fine with the icomfort ...

So I spoke to another guy at the dealer's and he strongly recommends against a modulating furnace unless the ducts are very good, sealed and even. Says that if the thing modulates down then there wont be enough air to reach rooms that have longer ducts or leaks. Again thats only the issue if the ducts are not good. So he recommends against the modulating one.

He says if ducts are too small the blower output can be limited to prevent it from howling. Not what you want but it needs to work.

So I am still on the fence about what to do. a modulating furnace is 800 more and over its 15 yr life thats not much abut I dont want to be stuck with a not so well working more expensive furnace.

on the other hand it sounds like a furnace that regulates down to 20-40% (or whatever they go down to) would heat the house even better as it would take longer to heat up and the house would be heated more evenly.

Still he says he installed man modulating ones in older houses and often there are issues and the furnace has to be operated as 1 or 2 stage. that would suck.

Does this make sense ?

Just another homeowner here, currently working on HVAC metal duct problem and saw this thread.

Have you considered working backwards on the desired tonnage of a new furnace by measuring your returns' square inches and adding them up? Rule of thumb is 200 square inch per ton. Eg, I have a ten year old 5 ton duo stage Trane, so my returns should add up to 1000 sq inches total. I didn't even know about all this until just recently while working on conditioning two crawl spaces through which hvac ducts run and started studying up on duct sizes and load. Good luck.

Below is an easy to understand video by a HVAC company which explains the above.

Here is a link that might be useful: David Jones-HVAC

the return duct going into the furnace is 25x10:, 250 sq in ... seems a bit small.

the smallest furnace I can get is 3 tons ... my ducts are good for 1 ton .... will this be an issue with howling?

This post was edited by Matt499 on Thu, Oct 2, 14 at 0:18

My suggestion is to add several more returns to your home strategically located for improved airflow and comfort. Also when you decide on furnace add a pleated media air filter cabinet.

In fact, your complete ductwork system should be looked at both supply and return.

IMO

A 25X10 return is too small for a 70K BTU furnace. I suggest increasing it to at least 25X16.

I don't agree with the Lennox dealer. The Lennox modulating furnace can go as low as 35% capacity. So the 66K BTU size could operate down to about 23K BTU. That happens to be the same as the low stage on my 3-stage 60K BTU Carrier furnace. It works fine using my 30 year old unsealed duct work which run from the basement to the second floor bedrooms.

This is the reason you see advice to stay away from the big box installers. They are usually not the best installers. If they were they would not need Costco to help them get business.

Have to agree with Mike. Furnace though must be sized correctly. Not sure a 70 K is right.

And understand, 3-4 small returns are better than one large return especially for a home your size. Do it, you won't regret in both comfort and noise.

IMO

all area inside the house (including hallways, staircases, entry and such) comes only to 2300 sqft. The house is old, so isolation is not great. but 70k btu seems like a lot....

Most furnaces seem to be 3 ton...

It is near impossible to add ducts or return airs but it might be possible to install a few smaller returns. As long as they all add to what is needed would it be ok?

The input and output of furnaces are specified in BTUs, not tons. A 3 ton furnace would mean 36K BTU. The most common furnace sizes are in the 60K - 80K BTU range.

The winter design temperature for Vancouver is 24 degrees F. This is relatively mild for a location so far north. The 70K BTU furnace should be fine, but a load calculation should confirm this.

The return at the furnace should be reworked to be bigger. Adding another return even if it is small is helpful. If your old furnace did not cause your duct work to howl, then you should be fine with the smaller furnace.

Guys, thanks for all the advice!

Update:

I spoke with another installer he took more effort to evaluate the furnace size requirements.

I decided to go with Lennox and in the end it comes down to 50, 70 or 100 kBTU.

The 50 is too small the 100 to large and what I would have needed is in the range of 60-70 so I will be getting the 70kBTU modulating furnace with icomfort control.

The supply ducting is actually two trunks of 7x14 (I didnt see the second one). The return ducting is still a little small and we will install one extra return and more if needed.

Hopefully this will work out :)

To clear up some info/questions posted earlier. The Lennox will modulate both up and down. For the longest time they would only modulate up, they finally did a firmware update. Just make sure that in the staging setup menu, "Load Tracking Variable Capacity" is selected, not just "Variable Capacity". I forget what the default setting is. Opinions vary but personally, I have seen no quality issues with Lennox that makes them any worse than other brands. With any brand you run the risk of installation/manufacturing errors.

can the user access all those settings or is that dealer only stuff?

In theory, it's dealer only, and you should make sure they do it when they install. In practice, you can get into the dealer menu yourself and check their work/change the settings yourself.

Since you have selected the SLP98v modulating furnace, I think the 70 K size is a mistake. I would go with the 90 K size. Won't hurt you a bit.

IMO

Here is a link that might be useful: SLP98v

It too late now :( I thought the issue was getting a furnace too large? The 70 should already be a bit too large

May not be an issue. Obviously you don't understand how a modulating furnace is supposed to work. You have a BTU range usually between 40% and 100% of output that operates, ie moves up and down in small increments based on demand.

My point is that 70 K size may be tight when you have your low temps. You have a large home.

Take the time to report back on your new furnace's operation, nat gas usage, and comfort during the dead of your winters.

Good Luck!

How was the 70K sizing determined? You need a load calculation, no matter what type of furnace you put in! It is still possible to oversize a modulating furnace, I have seen it done. The consequences are not as bad as oversizing a single stage furnace, but you won't be able to take as much advantage of the full modulating range that you paid for.

The OP has a 2000 sq. foot house (plus 800 sq. ft basement) in Vancouver. The winter design temperature is 24 degrees. His 40 year old 110K BTU furnace put out 85K BTU when it was brand new. I would think a 70K @ 96% efficiency is going to be OK.

I agree with Mike. All I saw was the 2800 sq ft. 70 K should be just fine.

Against that oversized old furnace, OP should see some nice fuel savings.

TD

The furnace is in and although its not very cold I am running it to see how it works ... So far I like it a lot. Cant hear anything really, cant feel hot air blowing around and the temperature seems very constant. A great difference to the old furnace that made it either too hot or too cold

The old furnace was 110 but maybe only put out 50-60 or so?

I did measure all rooms including stairs, hallways and such and it comes to about 2300. The entire inner surface of the house is ~3200 but lots is taken up with closets, walls and what not.

The basement has electric heating. it is laid out as a rentable suite so it is not necessary for the furnace to heat the basement as well. The house is a split level design and probably only 2 of those 4 split levels need to be heated much.

I could not find anybody who would be very interested in doing a load calc. But I think the 90 and 110 k units would be too large.

Take in mind it was heating enough with the 50 k effective old furnace...

Mainly however, its in so no second thoughts please ;)

The two guys who installed it very competent ticketed guys so I feel good about the install.

hvactech42 mentioned something about the staging setup but I cant find it. It seems thee were more setup options earlier that went away thats weird but I need to work with the thermostat more..

What did you do about adding returns and a box filter cabinet?

TD

Here is a link to the iComfort setup guide. It lists and explains all the settings in detail.

Here is a link that might be useful: iComfort Manual

the icomfort thing already died (after 1 day) .... great quality

What did you do about adding returns and a box filter cabinet?

TD

the contractor said the returns are actually quiet large and to see how it works and add more as needed. He gave 3h of duct work for free should it be needed.

I didnt get a special filter he said the main benefit is that you can leave it longer before changes but if you have a normal quality filter and change it frequently it is as good (unless you have asthma, etc).

When you say pleated filter are you referring to a normal thickness filter but pleated (I had that before from 3M) or a thick 2-3" filter pleated.

They will install it if i want. Should I get the filter cabinet for the thick filters?

Another question does my furnace (no heatpump) NEED a outside temp sensor or is it just used for display purposes on the controlelr?

The 4 inch filters have less air resistance than the 1 inch filters. The reason for this the thicker filers have much more surface area allowing air to flow more easily. They are more expensive but in the long run you save money by changing it less often.

Which thermostat did you buy? Some thermostats have software algorithms which take into account the outside temperature to determine if the furnace should operate in the low or high stages. It is a good feature to have in that the furnace operates in the low stage more often and potentially saves money.

looks like the Proprietary Lennox I comfort. This is needed to take advantage of the features of this modulating furnace to allow for full functionality of the small increments of the operating range.

On the returns, I thought you were told in earlier post about being undersized.

And yes, I would get the 4-5" pleated filter media cabinet. Should have been installed with the furnace.

IMO

I don't know how the Lennox thermostat decides how to modulate between 40% and 100% of capacity, but I would hope it takes into account the outside temperature in the decision making. If it does, then I am disappointed in the contractor not installing an outside temperature sensor.

SLP98v Product Brochure

Here is a link that might be useful: SLP98v Product Brochure

The brochure implies the outdoor temperature is used as an input to the control algorithm.

Did you use the contractor who was discouraging you from buying the modulating furnace? You often see contractors discourage customers from buying equipment they don't know how to install.

the guy who installed it appeared very competent. He said those slp98 furnaces did have lots of issues with sensors and condensation on heat exchanger that was fixed 1.5-2 years ago and now run pretty good...

A guy will come and install a temp sensor for free tuesday (was on the original quote) and also install a 5" filter box.

No returns yet, i will run for a while first and figure out the best place to add one. I could easily add a return right by the furnace in the basement but i dont think that would be a good idea as all it would do is suck air mostly from the basement not so much from the other 2 returns anymore ...

I have the lennox icomfort controller. today it works again. it defaults to the load variable staging thing and in some of the menues the blower output was 970 cfm. this was factory default. not sure why this is, it should blow much harder, but my ducts should handle that well.

What a saga this is. I wish there would be one competent guy who just gets it done right without having to be involved with this for months ....