Ok, I gotta ask. Why would your a-coil get clogged up with dog hair? The coil should be downstream of the filter, so it should be on the clean side of the air flow.

Unless there wasn't a filter....... :bigeyes:

Seen it many a time.:bash2:

oh yeah, there were filters... never "not" a filter in place.... this is a counterflow (downdraft) system, system is 19 years old, 1 year less than I have lived here---- probably 8- 10 years ago, I had to do the same thing/// though it wasn't -10* outside at that time, it was cold enough to need the furnace to work, I had a little more time to mess with it as the house wasn't cooling off as fast as it was on that -10* night between last Christmas and New Years.... but that other time that the furnace started acting stupid since it wasn't as cold out, I could take the time to pull the cover and clean the coil.... still had to pull the water heater then....this time it was faster to just cut the lines and yank the coil, reassemble and relight to get the wife off my behind because the house was cold...
we have been dog-less since about last Turkey day, 1st time since we moved in here. my son bought his own home and took "his" dog with him...
(still got 2 cats to put up with though) hopefully once winter and also spring rains are behind us I hope to get another....

but now back to talking about tankless water heaters...

one thing that I was wondering, can I just plumb the exhaust into the furnace exhaust, like my current tank type water heater is set up?

Taylorjm, I'm a commercial HVAC tech and know all about pre and post purge. I'm pretty sure mine fires off in few seconds max and I will see if I can time it soon.

I pulled a 50 gallon electric water heater and replaced a 9 SEER heat pump with a 16 SEER one and you are correct, I did not notice any change in my power bill. I'm not sold on all this efficiency crap.

I installed my own 9.5 gpm Rheem unit that was around $1300 at that time with the valve kit and tax. Looks like Home Cheapo sells it now for $1199.00 + valve & tax. I also had to run 60' of 3/4 black iron pipe when I did the install so that would add to the bill if you are paying someone. Yes, they run more money but they free up space and that is what I needed. I will never go back to a tank type, but that is me.

Not to change the subject or steal this post but I have no experience with pex, what do you people think about it? I was a copper only guy until I moved in my current house 17 years ago and now I'm sold on CPVC.

Not likely.
What type of flu is the furnace? Less than 80% with a double wall pipe? How large is the flu? Most tank water heaters are around 30,000 BTU, and the tankless are well over 100,000 BTU, if not 200,000 BTU, so it's not likely that the furnace flu is large enough to be able to handle the exhaust. Plus, if you get a 90+ water heater, it will vent in PVC. If the furnace you have is 90+ and vented in PVC, no, you cannot put two power vented exhausts into the same outlet. First of all, its illegal. Second, you run the risk of backflow. :beerchug:



I like it on remodels of old houses where there isn't a lot of room, or risk of freezing. It's easy to run, and works as well as PVC. Would I do new construction with it? Heck no. But it works good as a replacement. My personal preference (on new construction) is also copper, but I've done a lot of (C)PVC, and it works just fine. I just don't like the funny taste for the first few months. You just can't go wrong with copper. Plus, it seems to last forever. But it's sooooooo expensive!

I am learning a great deal. Thank You!!:popcorn::popcorn:

You need a dedicated flue for tankless.

The tankless type also pull combustion air from outside.

On the 90+ it is a separate schedule 40 PVC pipe.

On the 80+ the intake is in the same pipe as the flue exhaust. IIRC the intake is in the outer pipe and the exhaust is in the inner pipe.

Personally, I would use copper, just because it has been time tested to be reliable. Pex would be next on my list, but I'd have to research the best kind of crimpers/clamps again and see how they are holding up. I don't care for cpvc for water supply lines. I just don't trust glued connections for pressurized pipe. I know the cement isn't really a glue so to speak, but I just would worry one of those joints wouldn't get applied correctly. Just my opinion.

I'm not arguing....
But I've seen just about as many copper lines that didn't get soldered right as I have PVC fittings that didn't get glued right. Seen copper come apart, seen PVC come apart. One time, I saw a 90° copper elbow blow the outside corner, because the plumber didn't deburr the pipe after cutting. It was on a hot water circulation line, and the rolled edge caused cavitation to orrur in the elbow, eroding it out. That was a new one for me....
I've also seen pex fittings blow off, iron and galvanized rot out..... so, they all have issues one way or another, lol.