After ours was installed I stumbled across a company that makes an all in one unit called Eternal Hybrid (link below). You may want to contact them and see about getting the energy efficiency specs to go that route. I think Navien also makes an all in one system now too. I would think either company would be able to give you more accurate energy specs and better answer your question. The other thing to keep in mind is that without the loop (& pump), you are in effect wasting gallons of water waiting for the hot to kick in--think showers, sinks, etc. How much does the water wastage cost in terms of both water & sewer bills + the unnecessary waste of a resource? In addition to washing machines not pulling enough water through at a time to trigger the heater and then remain on long enough to actually get the water down the line to the machine, some dishwashers are having problems too. Here is a link that might be useful: Eternal Hybrid Hot Water Heater Site

You've probably never been in a home with properly sized ductwork. Don't feel bad, it's estimated that as much as 3/4 of the heating and cooling systems in the US are oversized. 2 stage and modulating furnaces are better, but I've lived in a home with both, and both can be very comfortable and the single stage equipment doesn't make it feel more dry that I can tell. BUt you are correct, multistage cna reduce the sense of dryness you might get with a less than ideal system. THe RH of hot air is lower than cooler air, but cool air can make things feel drafty. That's why radiant heat is popular. You essentially have very, very low air velocities and much of the heat energy is indirect infrared heat which make you feel warmer, similar to direct sunlight. Keep in mind too, that unless you have an outdoor rest control for hte boiler or to sped up or slow the circulator, most hydronic air handlers are single stage for heating. So the heat is no different than a furnace. Worse, as you reduce BTU's to the coil, the airflow speed is usually ocnstant, so air temps get cooler. My point being, that a properly designed and installed furnace won;t make it feel dry even if single stage. But yes, oversized furnaces and those with restricted airflow can. Vairble capacity will always make the system more comfortable, but it will cost more. Radiant heat overall is superior, but the installed cost is much, much higher. That's why it fell out of favor. Same reason drywall took over the market and plaster disapeared. ITs' primarily a matter of cost. It's also why stone and brick homes aren't built anymore and concrete homes are the minority.

I think there are a lot more folks here who have experience with the gas tankless heaters. Thus the lack of response. The main issue w/ electric on-demand heaters is the massive amp draw to heat the water. I did a quick look, and one unit that'd do 2 gpm at a 60 degree F temperature rise (maybe enough for your shower and sink in the winter) takes 80 amps to do that. That might require a service upgrade that'd be pretty painful financially. And I'm not sure if you can run a conductor that big inside your walls without conduit as protection. You've probably read that gas heaters have their own issues. The equivalent one is the need for a large gas feed (and possibly a new meter to meet the demand). But that's relatively low-tech piping that has to be run. Ditto on the need for expensive vent piping if you put one inside. And don't forget that, if your power goes off, no hot water. I guess there's some potential to mount a gas tankless on an outside wall, which is what we did with our Noritz. That gets rid of some of the issues, but then you need to make sure none of that piping is going to freeze. I'm in GA, and piping in outside walls makes me nervous here. That'd increase by a big amount for the DC area. There are lots of pros/cons/tradeoffs. Putting a bigger (and preferably more efficient) tank heater in your basement likely is going to be the cheapest option. Going to either type of tankless will save you on waiting for hot water, and it may save a little on energy usage, but that's going to come at a significant additional cost.

The point of a tankless water heater is to have a continuous supply of hot water that, unlike a standard water heater, will not run out. It can only provide instant hot water if the tank is at the point of use. There is nothing magic about it that will repeal the laws of thermodynamics and fluid flow. If there are many feet of piping that the heated water needs to run through, particularly if some of the run is in unheated space, there will be the type of lag you are describing. This is because the heated water has to displace whatever cool/cold water has been sitting in the pipe, and because that heated water will also will lose a lot of heat to the cool piping until that piping gets to be about the same temperature as the hot water. Only when the sitting water has cleared and the piping is heated up will you get water coming out at the temperature you want. This is not unique to tankless units...it's true of any type of water heating system where the heated water has to travel a bit before it gets to the point of use. If you want hot water faster, you'll need to move the tankless unit much closer to where you are using the water.