I currently live in a mobile home, and it has some issues with the existing forced air system. Some of these can be fixed, but others are inherent problems with the design.
The two ends of the house are constantly colder than the middle. Specifically the kitchen and master bedroom. There is one heat register in each room, except the living room which has two. In other words, the same size register that heats a small bedroom close to the furnace is expected to also heat a large bedroom or kitchen at the farthest points from the furnace. Not only that, but the kitchen and master bedroom both have 3 exterior walls, and large windows... In addition, it turns out the furnace does not have the necessary capacity to maintain temp when it's -23F outside. (57kBTU in, 45kBTU out)
Currently, there is a 30 gallon electric water heater, and besides not holding enough hot water, it is costing me a fortune to run. I've opted to upgrade to a Rinnai RUR199in tankless gas heater, as it seems to be a good model, and is actually approved for mobile homes. According to the manual, it is rated for combination potable water/hydronic heating applications.
Originally I was considering small direct vent wall furnaces, but those are about $ a piece. I'm starting to think hydronic may actually be less expensive... Small panel radiators are quite inexpensive, at around $ per room, and pex is cheap too. Pumps and heat exchangers are where the cost comes in.
I plan to install a make up air unit (Electro Industries 1kw electric heated, with power damper, fan, and filter) as there has been an issue with cold air backing into the dryer if the bathroom fan or range hood are running. Fresh air is also nice. That said, I'd rather not pay to electrically heat the incoming air, so I'll heat it with a hydronic coil and disable the electric heating on the unit. Therefore I already need a heat exchanger, and at least two pumps. My question is, do I need a pump for each zone (kitchen, master bedroom, bathroom towel rack/radiator, and makeup air unit)? Or will a single pump (not including the pump on the potable side of the heat exchanger) with zone valves work?
Cost wise I'm not sure which makes more sense, but the installation of two combustion appliances and venting will probably add a good bit to the base price of $ for both gas wall heaters. Also, given the small btu load (combined 30kBTU) and gas being rather cheap it won't matter much, but the tankless water heater is supposedly 96% efficient, while the wall furnaces are 82%.
Any thoughts/opinions, safety concerns, maintenance concerns, etc. are all much appreciated!