Closed Crawl, Radon, DHW Replacement, Sump, etc…..
I recently bought a house that is in general working order but needs some upgrades.
First, the problems:
– The current 30 gal DHW tank is probably on its last legs. It is located in the vented crawlspace and is not installed properly; it is sunk in the ground ~2 ft and has incomplete retainment surrounding it (see picture). This is the low point in the crawl and there is no sump pump currently installed.
– The house failed the radon test by a slim margin and will need mitigation.
– The furnace is in the crawlspace and does not have ducted combustion air.
This is the work I am considering:
– Ideally I would like to replace the DHW tank with a closed combustion tankless unit. The cost may be prohibitive if the main gas line is too small, so I may need to go with a closed-combustion storage tank unit. The benefit of going tankless would be that I could use the existing hole that the tank sits in now as a sump. Additionally, bc it’s in the crawl, installing a bigger tank may be difficult if possible at all.
– Install a sump pit/pump or leak sensors w/ shutoff valve on main.
– Provide high/low ducted combustion air to the furnace. Replacement w/ closed combustion furnace at this time is not in the budget and the unit, while 18 years old, is in fine working order.
– Install a passive radon mitigation system w/ perforated pipe per EPA specs. Vent using the current DHW exhaust chase but re-line with PVC. This assumes the closed combustion DHW can be exhausted through the wall, but I am not certain if that would work or is allowed. I plan to monitor the radon in the house and the system could be toggled to an active mitigation system by depressurizing under the poly via an exhaust fan installed in the attic.
– Seal-up the vents and carry the poly liner needed for the radon mitigation up the wall to first row of brick (see picture), then insulate the walls with 2″ of XPS or fire-rated polyiso so my floors can be warm and my water lines and mechanical equipment will no longer be ‘outside’.
The DHW needs to be replaced, but I feel like I need to do everything at once. I’m posting here to see what everyone’s thoughts are on my proposed solutions. Also, I’m planning on doing much of the work myself, so if anyone spots any significant code issues/red-flags please let me know. The house is in Denver which uses the 2006 I codes. Looking forward to your response! Thanks.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Your prescription is sensible and comprehensive.
I don't generally recommend demand water heaters because of their expense, over-sized burners, and finickyness to hard water and low water flows - but in your case it may make sense. However, I see no evidence in your picture of water damage to the water heater so I'm wondering whether your concern is about ground water or a bursting pipe.
You might consider replacing the existing tank with an Energy Star power-vented tank and placing it in a more water-tight base, such as a concrete well tile with poured bottom. If there is a better location within the crawlspace, it's easy enough to relocate the plumbing.
Don't forget to air seal and insulate the rim joist area.
Thanks Robert. My concern is about a bursting pipe, there is no evidence of groundwater issues. If a pipe failed today it would be messy but may be OK bc the floor is dirt, once the poly gets laid out a leak becomes a much bigger deal I think.
From your picture, looks like you have black iron pipe for your gas line which would lead me to believe you have a 7" water column gas system. We typically need to run a higher pressure system for the tankless water heaters but can run 2 psi system and leave the rest of the house on the original low pressure system. The gas company will happily come switch out their meter for the higher pressure and you put a regulator at the meter to divide the two systems. Not a big deal at all, we do it all the time but I would leave this to the professionals. Everything else should be fine for a DIY if you pay attention to the details.
If you close your crawl space you must provide some sort of ventilation. Your choices are; supply only, exhaust only or a balanced system. For existing crawl retrofits, I always recommend an exhaust only system (continous running panasonic fan) - this could also help with your radon system. Although dilution is not a great solution for high levels of radon, people have had success with this for low levels.